Model Engine Maker

Supporting => Tooling & Machines => Topic started by: Stuart on August 01, 2015, 08:48:08 AM

Title: To the dark side CNC
Post by: Stuart on August 01, 2015, 08:48:08 AM
Well I must be mad


A brief introduction , as you know I have had troubles with bad drawings and have to draw up the parts in TurboCad to prove to me that it is all correct with the dims.

Now as I have the cad drawings it seems a bit silly not to that the next step and let them drive a machine for the small bits ( note the WS is small so a large machine is out of the question)

So after consulting with the financial management dept a order was placed with ARC for a KX1.

John S was contacted to do the install ( two crutches or wheels ) are not conducive to moving machines

After much internet reading PC  :hellno: specs for mach3 a refurbed optiplex for £70 with a twelve month warranty was purchced

Well the faitful day arrived  day arrived and the machine is on the bench .

The machine comes with a cd with the software and a A4 folder manual more about that in another post

The software was loaded USB driver installed ,config files  and gues what zilch it no work nothing zilch
NBG

More to follow with pics

 :cartwheel:

Stuart
Title: Re: To the dark side CNC
Post by: Jo on August 01, 2015, 08:59:00 AM
Well I must be mad

With my love of collecting machine tools/castings I don't believe I am qualified to comment   :LittleDevil:

More to follow with pics


Looking forward to them. Strangely enough Vixen was trying to tempt me with "one of his spare" CNC mills not that long ago  :naughty:.

Jo
Title: Re: To the dark side CNC
Post by: mikemill on August 01, 2015, 10:08:42 AM
Stuart
Sorry to hear your new mill did not fire up first time, no bout Arc Euro will sort you out.
I bought a CNC mill around seven years ago, and there is a lot to learn. If I can offer some advice, start by making a 1in square in a soft material like acrylic or delrin, go through the whole process, draw the part, use a Cam program or write the code in Mach, choose a cutting tool say 1/4in end mill with a shallow depth cut say 1/16in
Clamp your material to the table with a sacrificial plate underneath so you don’t cut into the table!!! and hit the run button, have your hand on the emergency stop just in case, and see what you get hopefully a 1inn square!
Good luck
Mike
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 10:11:13 AM
A bit more info

You will have to wait for the pics


ARC,s advert is a wee bit not up to date

The machine is fitted with a single shot lub system .
The comp specs are out of date for the current ver of mach3  ( they say up up W8 )
The spec is for a PP system which will only run up to XP USB is fine to W8 note you cannot buy a new PP machine with XP , but as the interface is USB now it's no problem

Next the software cd contains out of date software and incorrect setup files for the machine ,more later
The manual with ref to the machine setup is well out of date and continually refers to the parallel port setup  note all machines now sold have USB interface , the manual makes no reference to copying the usbmove.dll

Anyway I have it sorted and running under W7 64 pro.

To be fair to ARC they do state check the support site for up to date software but you have to have a machine to get the ser. And reg code to register with the site to do the files . :toilet_claw:

Back to the PC side as ARC test the machine it should be ok so it must be the software.
Uninstall all the files installed  :Director:
Reinstall the current Mach3 , move the dll file to the plugins folder, plug in the mill turn it on ,win7 sees the machine and install its stuff. Then W7 requested a reboot
Start up Mach3 and I am greeted with the welcome to the driver signing on , now when I had the setup files from the cd the pin out setup was for a PP not as I found a motion controller .

Then looked on the support site and found a more upto date file v1.6 installed this now the PIN numbers are different for the limits , spindle setup .
Press the jog on the key board it's alive  X Y and Z even the spindle goes round.
You have to think of the cutter moving not the table  :censored: I found that X and Y were backwards no prob a quick click and all is well
Now the thing homes correctly ( I will explain if any one needs to know )
The next was to set up the soft limits so the machine knows how big and were the table is to slow down before it hit the limit switches ( later in another post)
Now call me a wimp  with a test file loaded for the Sieg logo , Z  half way up  no tool fitted and the job centred up in the correct place , I pressed cycle start much whering spindle ran up to 3k and it did its stuff

At this stage I have a PC and KX1 talking to each other but I will explain about the soft limits later.
I now have to get it in the correct position ,PC on shelf ,monitor on arm
Then I need to get to grips with CAM

More to follow

Stuart
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 10:16:58 AM
Mike

The machine was OK as you see it was the out of date supplied software and incorrect XML file that fogged up the channel

Now that is sorted all is well well it moves and goes round with it doing the correct thing for the key pressed

Much more to follow re calibrating the movement , and getting my head in gear , I fear a lot of air cutting will take place

Stuart
Title: Re: To the dark side CNC
Post by: Vixen on August 01, 2015, 12:34:25 PM
Stuart
So you have bravely decided to enter the dark side of model engineering.

As you have already discovered, you are more or less on your own when it comes to getting it set up and working. Microsoft are only interested in selling Windows stuff, the machine manufacturer is only interested in selling machines, the CNC software people are only really interested in selling more copies of their software. None are really interested in owning YOUR problem, it's yours to fix. The CNC software is complicated by the number of hacked pirated copies of the software from the far east. Hopefully you have the genuine article.

Fortunately, you are getting to terms with your set up and the mill is responding to your wishes. I suspect there will be more work required to calibrate the axis etc. Stick with it, the effort will be worth it when it is all singing and dancing.

Then comes the fun bit, learning how to CNC machine stuff. This requires lots of time and patience together with lots of "machining air". It is safer that way, without the risk of the mill table, clamps and fixture getting in the way.

I discovered that to get the most out of a CNC mill, you first need to become good at CAD drawing. The drawings define the shape of the bits you are trying to manufacture, therefore you need to be very familiar with your chosen drawing package. Concentrate on a 2D drawing package, save the 3D stuff till later, much later. 2D drawings are all you need to define the pocket or contour toolpaths for you milling machine. 3D drawings are for high end multi axis machining centres, which are way beyond reach of our payscales.

Once you have mastered the drawings and using the software to convert them into toolpaths you can practice CNC machining on the mill. It is best to practice by machining air, that gives you time to hit the panic button if things do not go the way you intended. This will also teach you all about defining and using datums.  This is all about gaining experience and confidence.

When you start machining for real, you will soon learn about deciding the feeds and speeds. You will find it much safer to be very conservative with the depth of cut and the feed rates. It is better to go slow at first. You can always remove metal faster with a manual machine than is safe for a CNC machine. With a manual machine you can 'feel' the cut and ease off when necessary. With CNC you need to pre-define everything. So program the machine to make many small gentle cuts until you gain experience with different size cutters and material types.

CNC is not easy, it has a steep learning curve. It may not be easy but it does made the more difficult machining problems possible. It is a completely different experience to manual machining. I committed totally to CNC, soon after I got my first CNC mill to do what I wanted. Now I have a handwheel free workshop. That's not completely true, my lathe still has a manual tailstock.

So stick with it, take your time and gain the experience and above all enjoy the journey.

Mike
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 01:01:12 PM
Mike

Thank you for your input much of is has cemented my thoughts .

My motto is to take baby steps slowly

Yes the software is direct from the Mach3 web site and is now licensed as part of the machine deal ARC were very quick and professional in this . So no worries there

As to sorting out the problems yes you are alone , it did not help having the incorrect setup file supplied , but that's sorted.

I am a apple user and have had to relearn windoze , but as I built my first comp with a zilog Z80 many years ago , and spent a lot of my later working time doing BAS system software for a bank , I have the background to sort it out .

I use turbocad for Mac and have done for years so that bit is sorted ,a nice 27 inch iMac helps in that they are easy on the lamps.

Thanks again for your wise input I would guess that it will be a few weeks before metal is cut but off cuts of MDF may be done .
ARC supplied cut2d licensed copy as the CAM package , have you any thoughts on CamBam ( negative on this is they have stopped development on it but the first one is still being updated

Stuart
Title: Re: To the dark side CNC
Post by: Vixen on August 01, 2015, 02:00:32 PM
Stuart
You are going about this in a very deliberate and controlled manner. Take all the steps along the way and don't look for shortcuts.

You will find MDF is far more abrasive on cutters than metal. I would not consider using it. There are CNC foams available for test running a CNC program. However you will not learn about feeds and speeds from foam, you need to cut metal for that. Always use a hard aluminium HE 30 TF (6082) or similar. Avoid soft, bendable aluminum like the plague, it does not cut nicely and welds to the cutter. Same goes for unknown material from the scrap bin.

Always 'CLIMB MILL' with a CNC machine fitted with backlash free ball screws. Climb milling reduces the power required to push the cutter and the surface finish is so much better.

Unfortunately I have no experience with cut2D or CamBam. I use DeskNC, it works well and I have used it for years and have no intention of trying an alternative. Unfortunately the company went bust so it is no longer available. I guess all the low cost CAM packages will be similar, some easier to drive than others. Whatever package you chose, stick with it and become a proficient user.

There is no substitute for time in the saddle.

Mike
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 02:18:20 PM
Mike thanks for the tip on MDF

As to metal I always get my stock from m-machine you get what you order , it may cost a bit more but you know what you are dealing with.


As I have a free copy fully licensed of cu2d desktop I will take you advice and give it a good go before I jump ship.

I will post some pics later when the WS is a bit more presentable and the PC it out of the way it's on a stool at the moment .

As we all know you are not done with the plastic when you have got the machine , fixtures, tool holders all mount up as the other mill is R8 they will not fit so another setup is needed

Yes the mill has ball screws as standard so climb milling is on the cards the spindle tops out a 7k

Stuart
Title: Re: To the dark side CNC
Post by: kvom on August 01, 2015, 02:35:53 PM
I'm a CamBam user and can recommend it highly.  Easy to learn the basics, and the support forum is excellent.  It can also generate 3D machining output if you advance that far.

I don't use Soft Limits myself.  Once you center the spindle on the work origin and zero the XY DROs, it's simple to verify the machining limits.  Load the g-code into Mach3 and you can see the toolpaths.  If the piece is large enough for you to worry then you can jog until the crosshairs are at the X and Y limits to verify that the limit switches are not touched.

For most work my Z zero is top of stock, and I establish that using a 1" gauge block.  I first zero the Z DRO at 1" above the stock and run the program cutting air.  Then, rewind the program, move to Z0 on the DRO and set the DRO to 1.0.

Feeds and speeds can be a problem starting out.  I licensed a copy of Gwizard to calculate F&S, and I have broken almost no tools since then.

Another tool I use that's very useful is CutViewer, a milling simulator that can be integrated with CamBam.  It runs your g-code in software to show you what the resulting part will look like.  It also detects collisions (rapid moves into the stock).
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 03:08:40 PM
Thanks

That's the type of info a raw beginner need to know I will take a peek at CamBam as well as the freeby as Mike has said then stick with it better the devil you know


Stuart
Title: Re: To the dark side CNC
Post by: Floating around on August 01, 2015, 03:47:41 PM
Hi Stuart,

Welcome to the dark side!
I have used cut2d a bit and have found it Great, nice and simple is good when you are learning so many other things at the same time. You will find it a bit limiting in the long run depending how far you get in to CNC.
You may want to have a look at Fusion 360, it is FREE! Full CAD and CAM i have only had it for a week but sofar it seems very good. In fact much better than some of the currently avalable very expensive software that i bought ( it shall remain name less!)

Good luck.

H
Title: Re: To the dark side CNC
Post by: JimG on August 01, 2015, 04:09:41 PM
Another happy user of Cut2D.  :)   I got my copy with my KX1 about five years ago and it has been excellent for doing 2.5D.  There's a new desktop version available with more facilities but I haven't had experience with that.   I was thinking of using DeskProto to complement Cut2D for more advanced 3D work - I've had a look at the trial demo and it looks as though it will give me a lot more facilities to use with my fourth axis.

My KX1 has been excellent and I've learned to use it for making a lot of parts which I would normally make with saw, file, etc.   It fully compensates for advancing years and gives an accuracy that my failing hands and eyes would find very difficult to match.  :)  Instead of cutting air,  I run a second copy of Mach3 on my "big" PC which runs my AutoCAD LT and Cut2D.  I run all my new work on that copy and check out the co-ordinates to make sure I'm not ploughing through the table.  :)  I mix zero to top and zero to bottom with CAM so it pays to check that I haven't run with the wrong setup - I have done once or twice.  :)

Jim.
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 04:25:39 PM
Floating around


Just had a look at fusion 360 it's £185 looks like it's cloud based no good as I do not have a network in the WS
It's free if you are a student but at 68 and a OAP  I don't think I can swing that
Note if it's good the price would not matter I will add it yo the consider list

Jim thanks for the info I emailed vertric with my details on the cd and they upgraded me to the desktop version for free, thanks for the added details

Stuart
Title: Re: To the dark side CNC
Post by: Floating around on August 01, 2015, 04:57:16 PM
Hi Stuart,

Fusion 360, seems that they are hiding the free option!
If you download the 30 day trial,and install, click on the day countdown at the top right corner there will be a option to buy it as a startup company/ hobby user, this is free!
They seem to be working quite hard on it, last week they upgraded it to have lathe CAM, something that is rather hard to find at any reasonable price.
But that still doesn't help with out network.  Edit, it will work for 2 weeks with out network, then needs to sinc with the server and then can go another 2 weeks, bit of a flaf but might work.

Any way, might be a good cad option for in the house?

You are in for a great time, it is amazing to watch something pop out of a chunk of metal so fast. It is addictive!

H
Title: Re: To the dark side CNC
Post by: Jo on August 01, 2015, 05:19:13 PM
I think it is time to mention....

 :pics:

Not that I am going to buy one  but we would like to have a little look at your new machine   ;D

Jo
Title: Re: To the dark side CNC
Post by: Vixen on August 01, 2015, 05:21:20 PM
Hello H

Fusion 360 appears to require 64 bit versions of Win 7, Win 8 or Win 8.1 to run.
Mack 3 will not run on 64 bit versions of any of these OS. Mach 3 requires a  32 bit version of Win 2000, Win XP, Win Vista, or Win 7

CNC machining should be about hacking bits of metal to the required shape, but it soon degenerates to become hacking software instead.

Mike
Title: Re: To the dark side CNC
Post by: kvom on August 01, 2015, 06:53:26 PM
Fusion360, like Solidworks and several other modeling software products are for 3D modeling.  Only after the part is modeled do you produce a 2D view/drawing and export a DXF or similar for 2.5D machining.  There's a lot to be said for 3D modeling but for many the learning curve may be steeper than 2D CAD.  Once mastered, a 3D model can produce a solids file (.e.g, STL) that can then be used to generate 3D g-code.  That's one reason to select CamBam over a perhaps simpler program.

My workflow for the past 6 years or so has been to use Draftsight (free autocad clone) to transcribe paper drawings, export to DXF which then is loaded to CamBam for g-code production.  Recently I've been using Solidworks to model entire engines.  I have then used the models to create DXFs for some parts, but haven't yet machined anything from them.  Doing the modeling work on each part and then joining them in assemblies is very useful for confirming fits and dimensions.


Title: Re: To the dark side CNC
Post by: fumopuc on August 01, 2015, 07:49:29 PM
Hi Stuart, I am a happy Vcarve pro user with my little proxxon mill now since 3 years. First intention was to start with Cut2D but after playing around with the tutorials at the Vectric home page I have spend the money for the more expensive package. I am using the CAM section only.
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 08:21:27 PM
H

No good for the house I have a 150 meg internet but no PC only iMac ect. , ok I could boot camp windoze but it will upset the partition map of the fusion drive hence a no go

Hence the title the dark side being windows.

Thanks again for the the input as it is I have some software with the machine , TurboCad v8 for Mac so I will try that combo first if all that fails I will have to install a wifi booster to get a decent signal out to the WS and go with your surjestion

Thanks again for your input
Stuart
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 08:31:04 PM
Mike
I hate to tell you that mach3 will run on a 64 bit windows 7 with a motion controller that's how mine is running , however the PP will not run on any 64 bit only up to I believe W7 32 bit

Quote from Mach3 site note motion controller

"An appropriate external motion controller (options can be found on the Plugins page)
Desktop or Laptop with Windows 2000, Windows XP, Windows Vista, Windows 7, or Windows 8
1Ghz CPU
512MB RAM
Video Card with 32MB RAM(Large G-code files, especially 3D files will require a video card with 512MB RAM or higher)"

It's the PP that limits it as the DLL for the PP that can only run in 32 bit OS . That's why the switch to motion controllers USB or Ethernet has had to happen because the modern PP do not output 5vdc only 3.3vdc hence they do not have the power to drive the hardware


So my system is a core duo optiplex running W7 64 bit pro and it's fine no problems now I have the correct software , this needs to be the current ver in all cases else it will not run

Stuart
Title: Re: To the dark side CNC
Post by: Stuart on August 01, 2015, 09:15:56 PM
Tomorrow  Jo

I will get some up for you

Stuart
Title: Re: To the dark side CNC
Post by: Vixen on August 01, 2015, 09:42:35 PM
Stuart
Reading back through today's posts, I am so relieved that I do not have to start my CNC adventures with today's hardware and software.
A core duo optiplex running Win 7 64 bit pro driving Mach 3 software via an external motion controller. That is an impressive set-up.

I have an old 486 machine running Win 95 in DOS mode. DOS is a real time OS, whereas Windoz is not, therefore it needs the external motion control hardware. My control software is DeskNC which runs in DOS. I have used this stuff every day for the last twenty years, it may be old fashioned but it does exactly the same job as the expensive modern stuff. no more, no less. It does it without fuss and is totally reliable. Finding old PC's will one day become a problem for me, and then I will have to modernise. But until then.........

Mike
Title: Re: To the dark side CNC
Post by: Don1966 on August 02, 2015, 02:24:01 AM
It's the PP that limits it as the DLL for the PP that can only run in 32 bit OS . That's why the switch to motion controllers USB or Ethernet has had to happen because the modern PP do not output 5vdc only 3.3vdc hence they do not have the power to drive the hardware


So my system is a core duo optiplex running W7 64 bit pro and it's fine no problems now I have the correct software , this needs to be the current ver in all cases else it will not run

Stuart
Hi Stuart there are converters to handle handshaking.............http://www.epapersign.com/lpt2usb0/lpt2usb-features-and-functionality?gclid=CNLayMGdiccCFYI7aQodix8ChA

Don
Title: Re: To the dark side CNC
Post by: Floating around on August 02, 2015, 07:44:30 AM
Hi Stuart,

Thanks for the clarification. I have always run 2 computers, one slow/old dedicated windows box for the cnc machine and the other a faster more modern one at a nice comfortable desk for design and cam, (seem to spend a LOT of time there!) transfering the G code file between the 2 with a usb stick.
Trying not to go banging on about fusion 360... But it also runs happly on a Mac in OS10. I'm curently using it on a 4 year old macbook pro but with the latest version of OS10.

What motion controler are you using?

H
Title: Re: To the dark side CNC
Post by: Stuart on August 02, 2015, 07:57:14 AM
H

Now you have me interested runs on a Mac OS X 10.  I will try it out on OS X 10.11 B5 note I am under NDA on that system so there will be no detail except for it run or not


Thanks for the info I did not look hard enough

It will solve a problem no need to be in the WS in the evenings and can sit comfy at my desk

Stuart
Title: Re: To the dark side CNC
Post by: Stuart on August 02, 2015, 11:39:19 AM
Here are a couple of pic
(http://i905.photobucket.com/albums/ac253/lordedmond/IMG_0031.png) (http://s905.photobucket.com/user/lordedmond/media/IMG_0031.png.html)
at the left is the pipes fore the one shot lube system
note the rt is a 100 mm one

(http://i905.photobucket.com/albums/ac253/lordedmond/IMG_0030.png) (http://s905.photobucket.com/user/lordedmond/media/IMG_0030.png.html)

(http://i905.photobucket.com/albums/ac253/lordedmond/IMG_0032.png) (http://s905.photobucket.com/user/lordedmond/media/IMG_0032.png.html)
engine room

note the holes are the ser. no.  I have blanked it because you can use it to reg on the support rite

The WS is a mess please excuse a new toy comes in and they make a mess

if you look the front of the thing is over the bench but a heavy steel angle is to be bolted on to provide support although the thing is very rear end heavy weight wise its 80 Kg

Stuart
Title: Re: To the dark side CNC
Post by: jadge on August 02, 2015, 10:00:14 PM
Stuart: Welcome to the world of 21st century machining.  :stir:

I've been running a 4-axis CNC mill for the last eight years, and it opens up a whole new world. It allows you to design parts in a completely different way, but it requires a slightly different mindset. I tend to run 6mm and 10mm cutters as standard and I run at much higher spindle speeds and feeds than I would, or could, run on the Bridgeport. In HE30 I'd run a 10mm cutter at 3000rpm and 900mm/min feedrate. I can't turn the handles on the Bridgeport that fast.

I would disagree with some of the previous posters in some cases. Personally I'd go straight for 3D CAD. I find it much easier to use than 2D (essentially an electronic drawing board) and it allows you to build assemblies to make sure all the parts fit together properly. Speeds and feeds are the biggest problem. I wouldn't be too cautious, the tool needs to cut not rub, so make sure the chip load is sensible. I agree that climb milling gives the best finish (at least on some materials) and I tend to make the finish pass climb milling, but otherwise I don't worry about climb or conventional milling. I normally use a combination of both to get the machining done in the shortest time.

I use 3D models in my CAM software, even for 2½D machining. I also use backplotting software (NCPlot) that plots a toolpath from the actual G-code that has been generated. Rarely my CAM program doesn't generate G-code that matches the toolpath it thinks it is using. I used to air cut first, but don't normally bother now.

Here's the first part I made on my CNC mill, it wouldn't have been easy on manual machines:

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_First_Part.JPG)

For the curious the part is an end cover for custom common mode and differential chokes wound on iron powder cores. The chokes were carrying 50A at 600V, so the wire was heavy gauge with thick insulation. The end covers prevented the wire from being cut by the cores, and the curved radial grooves helped to uniformly space each turn.

Andrew
Title: Re: To the dark side CNC
Post by: Stuart on August 03, 2015, 07:08:58 AM
Thanks for the reply Andrew

I wil have to digest all the information given by you and others , but by ekk it's going to take some chewing

Yes it's a new mindset with far more fixtures and pockets to hold the parts I want to make

i do know that first cut into metal is going to be a bit twitchy


Stuart
Title: Re: To the dark side CNC
Post by: Stuart on August 03, 2015, 10:49:33 AM
Back to the soft limits these sit just inside the limit switches and also define the workable area .

They are set by homing the machine , change to work DRO zero these an drive each axis to the limit switch note down the numbers

Then go to the soft limits page and set them to just short of your note figures .

In use the software shows the work area as a dotted line then you can make sure that the job will fit , and second it slows down when approaching the defined area limit.

This give you belt and braces safety .

But a big note make sure you reboot mach3 if you change any soft limit as it needs to start up with valid data.

Others may not use them but I am new to this so any hand holding will be useful

So as of now the machine is in position bench support fitted to the front PC do da put on a shelf and the monitor thingy on a wall bracket

Have I said I hate windoze with a passion but it look with help of Floating Around I have found a CAD CAM package that runs on a Mac as well as the other one and he has explained how to get it for free if you are an enthusiast/hobbyist  legally
Their is no ser numbers only hour log on as the home equipment has a very fast connection it will be fine , one package to do both jobs , and it has a post processor for Mach3

Stuart
Title: Re: To the dark side CNC
Post by: jadge on August 06, 2015, 09:28:38 PM
I've never used soft limits; not sure I really see the need? One of the features of the backplotting software I use is that it gives maximum excursions in the three axes. So it is fairly simple to check the limits against the size of the part. This is especially useful in Z to ensure that the tool isn't going to get driven into the table.

Apart from the normal self-induced finger trouble foul ups I've had a few issues with my machine over the years. There have been a couple of electrical problems, both intermittent, one a dry joint and the second due to a poor quality copy of an industrial connector. I have had one Mach3 issue. Infrequently the tool would go racing off into the middle distance, milling through everything in the way. I eventually twigged that it only did it after a tool change. Turns out that somehow the tool change macro was changing to relative coordinates. I modified the post-processor to include setting absolute coordinates at each tool change. I also dumped the ordinary PC, running a clean install of XP, and changed to a controller running an embedded version of Windows. I haven't had any problems since.

Here are a few random thoughts:

I use mostly 2, 3 and 4 flute centre cutting end mills, and have standardised on 6mm and 10mm, unless I need a specific (normally smaller) size

Although my CNC mill and the Bridgeport are nominally the same hp, the CNC spindle is much faster, so I tend to program with smaller cutters running at higher spindle speeds and feedrates than on the Bridgeport. My CNC mill has a sort of 'quick change' collet system, which I have also started using on the Bridgeport for many of the smaller cutters

Almost all cuts are started by ramping down, or following a helix, to the required depth at about a third of the normal feedrate

I try and use as big a depth of cut as I can - you're paying for the cutting edges on the flutes of the cutter so you might as well use them

When cutting internal radii I use a cutter that is smaller than the radius; otherwise the angle of engagement changes rapidly and is almost certain to cause the tool to chatter

I use flood coolant on everything except, brass, cast iron and plastics, mostly to wash away the swarf rather than actually cool anything

'Touching off' carbide tools is a PITA. I chipped so many cutters I invested in an electronic tool height setter that automatically fills in the tool table

Andrew
Title: Re: To the dark side CNC
Post by: Stuart on August 07, 2015, 07:31:29 AM
Thanks for the info Andrew

As is normal in engineering in general there are many ways to achieve the same result

Still getting to grips with things as has been said its a steep learning curve


Although my machines are much smaller than yours I do not nibble with cutters and like you I will use a smaller cutter to enable more flute to engage with the HP I have


Stuart
Title: Re: To the dark side CNC
Post by: kvom on August 07, 2015, 01:05:43 PM
For touching off I use a 1" gauge block, and have never chipped a tool.  I jog up until the block slides underneath, the down .01" and then up by .001".

I use air blast to clear chips.  Tried coolant, and it was messy.
Title: Re: To the dark side CNC
Post by: maury on August 07, 2015, 01:48:30 PM
I have just tuned into this interesting thread. Lots of good info. It demonstrates what was said in one of the early responses, every CNC user is on his own to build is system within his constraints and to solve his own problems.
Good stuff.

KVOM, I don't want to hijack the thread, but this might be relavant. Your response on "touching Off" intregued me. I have been dealing with backlash issues on my machine and for many reasons I don't want to go through the process of rebuilding. For setting the "Z" I have been using my Reference tool, dropping down to near the top of the work, and stepping down .0005 per step, using a .005 feeler guage  to touch against. Then step down .005. This has not been very reliable.
Question: do you believe if I step up like you do my "Z" settings will be better?

maury
Title: Re: To the dark side CNC
Post by: Hugh Currin on August 07, 2015, 03:45:05 PM
For touching off I use a 1" gauge block, and have never chipped a tool.  I jog up until the block slides underneath, the down .01" and then up by .001".

I use air blast to clear chips.  Tried coolant, and it was messy.

I do the same. However, you need to be careful lowering the tool onto a block (i.e. don't do it). if asked to move say 0.010" down the machine will use all its capacity and force to complete the move. There is no "feel" in lowering the spindle. I typically move the tool a little below my 1" block. Then move up by 0.010" steps till the block slides under the tool. Then lower the spindle by 0.001" steps. Remove block from under tool, lower spindle, slide block under tool. Continue until block won't won't slide under and set tool length. It goes quickly and sets the Z axis to take up backlash on lowering moves.

I've had good luck with mist coolant. It's a little messy but not nearly as bad as floor coolant.

Thanks.

Hugh
Title: Re: To the dark side CNC
Post by: maury on August 07, 2015, 05:08:59 PM
Hugh, the way I understand what you wrote is the tool is lowered until it touches, ( the way I do it). I understand the  way KVOM does it, he raises the tool until it just touches. The difference is which way the backlash is taken up. On Most CNC systems this is not an issue, but I'm finding it is on mine.

maury
Title: Re: To the dark side CNC
Post by: Hugh Currin on August 07, 2015, 08:46:13 PM
Hugh, the way I understand what you wrote is the tool is lowered until it touches, ( the way I do it). I understand the  way KVOM does it, he raises the tool until it just touches. The difference is which way the backlash is taken up. On Most CNC systems this is not an issue, but I'm finding it is on mine.

maury

Maury:

Yes, I agree on the backlash. Using LinuxCNC I have the few thousands backlash accounted for, but it's still best (I think) to take up the backlash on a lowering move. However I don't lower the spindle onto the block when moving down. I move the block to the side, lower the spindle, then try to slide the block under the tool. So my process is:

1. Move the tool down (not over block) until block won't slide under the tool (visual no increment)
2. Move tool up by 0.010" steps till the 1.000" block slides under the tool
3. Move block to the side away from tool
4. Lower tool by 0.001"
5. Slide block under tool
6. If the block slides under the tool repeat 3, 4 & 5  -  If it doesn't slide under continue to step 7
7. You're done, set length compensation and go on to next tool

The Z axis drive will use all its power to complete the move requested. If the block is in the way it'll put a lot of force on the block and tool. I like to avoid this.

If I'm using only one tool, I'll typically lower the tool within 1/4" or so of the work. Then raise the table by hand using a piece of paper for touch off. Much better feel moving the table by hand than using the Z drive. Obviously for a knee mill where one can move the table up and down.

Does this make sense? Much harder (and longer) to describe than to demonstrate.

Thanks.

Hugh
Title: Re: To the dark side CNC
Post by: maury on August 07, 2015, 09:25:35 PM
Hugh, thanks, I understand what you are doing. I was just wanting advice on which direction the backlash should be zeroed to.

Most of the time I just ignore the backlash, but right now I am trying to make some +- .001 parts that have setups on all 4 sides. I know this is a challenge, and am finding I have to do the precision part on my Bridgeport.

maury
Title: Re: To the dark side CNC
Post by: kvom on August 08, 2015, 12:45:21 AM
That's exactly how I do it Hugh and Maury.

If you have backlash in the Z axis I doubt it makes much difference how you set zero since the spindle is going to move up and down when machining.  However, if your cutting is all -Z movements, then after setting Z with the block you can try to move up a few thou, then down the same amount and see if the block still just slides under.
Title: Re: To the dark side CNC
Post by: Dave Otto on August 08, 2015, 01:27:25 AM
Add me to the list guys; Hugh, kvom, I set my tools on my converted knee mill at home the same way. for the most part I use a .1" gage block and sometimes I also will use a .001" feeler gage.  The knee mill is really lacking in Z travel so a height setter for the most parts is out of the question.

At work I have a nice 2" tall tool setter with a LED indicator light. When you get right down to it you can turn the LED off and on with one click of the MPG set on tenths. It is nice to have a relatively tight machine.

For cooling and chip removal I have a dual nozzle Micro-Drop system that I love. it uses a very expensive cutting lube/oil that is delivered to the tip under pressure at a metered rate. there is a second line that supplies air that carries the drops of oil from the tip to the cutter and part. The air and liquid are independently adjustable. It does not go rancid, smell, or fog up the shop. One gallon of the lube will last me many years. I have a solenoid wired into my CNC controller so the Micro-Drop is controlled by the the G-code.

I know a lot of guys get by with out limit switches and soft limits; but a good set of quality limit switches and properly configured soft limits sure are nice. My switches (Omron) repeat to a thuo or less; so if something happens and I need to restart Mach or the PC after homing I can go back to work with out having to re-do my G54 fixture offset. Also I can rapid full speed into the machine limit switch and when it gets to the safe distance it slows down at a controlled rate until just before it hits the limit switch and stops with out hitting it.

There has been more than a few times when soft limits have prevented a crash from a tool offset that didn't get set right.

I have servos on my mill and they move at a pretty good clip +120ipm. it is nice the have the machine not crash in to the the hard stops especially in the very short Z axis.

Just some of my thoughts,
Dave
Title: Re: To the dark side CNC
Post by: Stuart on August 08, 2015, 07:34:36 AM
Dave
That's my thought on soft limits , but as a very raw beginner to the world of hands off machine I am posting my findings as first time user , I am just starting to crawl ( to use our own development in life)
Not looking forwards to the terrible teens when the think they know it all .

John MBE is coming next week for some hands on


Stuart
Title: Re: To the dark side CNC
Post by: Floating around on August 08, 2015, 04:04:58 PM
Hi Stuart,

Glad I could help!

H.
Title: Re: To the dark side CNC
Post by: jadge on August 10, 2015, 01:47:34 PM
Agreed that CNC can be a very steep learning curve, and I still have a huge amount to learn. It annoys me when 'experts' say it is cheating, as all you need to do is press a button and out pops a part. I usually tell them that since it is so easy they can come and use my CNC mill, but if they damage it then they pay for a new one. No takers so far!

The only way to learn is to give things a go. It is surprising how complex a part can be using only 2½D operations. I made 8 of these heatsinks, using only 2½D operations, a couple of months after starting from zero with CAM and CNC milling (I was already reasonably proficient with 3D CAD):

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_Heatsink.JPG)

The heatsink is about 300mm square, and was a challenge to jig as that is bigger than the Y-axis range on my CNC mill, so it had to be done in two bites. All the small holes are M4 - I use a compression/tension tapping head on the CNC mill.

Using 3D operations opens up a whole new world, like this bevel gear (it is a true bevel gear, not one of the normal approximations):

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_Bevel_Gear.JPG)

And for 4th axis anything goes, like a bevel pinion:

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_Bevel_Pinion.JPG)

Or worms:

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_Worm_Machining.JPG)

When machining the worms I had all sorts of issues with feedrates. Basically the radius compensation 'feature' in Mach3 is less use than a chocolate teapot. I ended up using inverse time feedrates, G93. Although the worms look complex the G-code was hand written. The basis of the program is one G01 move in X and A. After cutting keyways the worms look like this:

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_Worms.JPG)

If I can make parts like this then I am sure everybody else can too.  :ThumbsUp:

Andrew
Title: Re: To the dark side CNC
Post by: Stuart on August 10, 2015, 02:54:18 PM
Andrew

I have gone a shade of green no I have eaten something that has upset me but the learning curve has just got a whole lot steeper can you go steeper than vertical ?


Just got my 4 th axis set up working so when I need it it's there , got to sort out some tooling plates

But things are slowly coming together just waiting for John MBE to sign off on the setup and things should be OK

Decided to jump ship on turbocad for Mac and go down the Fusion 360 route , it's free works on the in house macs so I can do the CAD/CAM in comfort

Thanks again for your input
This must be the longest I have had a new machine and not cut metal

Stuart
Title: Re: To the dark side CNC
Post by: cfellows on August 11, 2015, 10:22:45 PM
Stuart, you are going to love the 4th axis.  Since building my 4th axis, I've used it to make spur gears.  I also made a right angle drive for the spindle so I can use the 4th axis to make helical gears and do very nice and accurate threading.

(http://i192.photobucket.com/albums/z195/cffellows/IMG_3632_zps0a1b895b.jpg)

(http://i192.photobucket.com/albums/z195/cffellows/IMG_3646_zps2749141d.jpg)

https://www.youtube.com/watch?v=6HO0DICwnSk

Chuck
Title: Re: To the dark side CNC
Post by: Stuart on August 12, 2015, 07:08:36 AM
Thanks Chuck


Well I have now got it in a position where I am confident that the PC thing and the mill are talking to each other correctly ,with all the axis going the correct way .

So as a first cut, I cut a test cut ( supplied tap ) file of the logo on the mill, well it did what it says on the tin , the logo completed the text was the right way round and the circle was a circle and no step in the circle at the finish .

So things are progressing managed the tool offset ok bit of a faf but not to bad , at least it did cut were I wanted it to

Stuart
Title: Re: To the dark side CNC
Post by: Jo on August 12, 2015, 07:33:52 AM
Stuart, I am jealous that you have all this time to set up CNC and learn how to use it.

Mr Silky has been living with me for months now and we still have not learnt to cut threads together :-[

Jo
Title: Re: To the dark side CNC
Post by: Stuart on August 12, 2015, 08:28:53 AM
Well Jo

I have something that you do not have yet unlimited time to play ( well not quite Linda,s jobs take priority ) then when my pain is under control (16 + painkillers a day) the time is mine.

I thought the Hardinge lathe was the bees knees for threading 🎁

Like these CNC machines it's the operator that has to be trained to understand how to talk to it when you can converse then things can be done untill then it's hard work.

Now I have to learn Fusion 360 CAD CAM  that's getting there , it's a bit easier than learning C++ and the funny BAS system for the banks HVAC plant , Swift was pretty quick as its C bases but different API,s
Fusion is good and as was pointed out FREE to hobbyists  windows and Mac and can be used on any number of computers ,it's your account logon that authenticates the software , OK it's a cloud based storage but that's what makes it portable .
I have done some bits for the upcoming build in parametric ( not sure that's the right word) modles and done the tool paths  , but as I like to know what is going to happen before I press go I am not 100% yet

Stuart
Title: Re: To the dark side CNC
Post by: Vixen on August 12, 2015, 09:13:32 AM
Hello Chuck

I like your 4th axis set-up. It has got me excited and thinking about making one for myself.

I see you are using a HUGE stepper motor and I can understand the need for plenty of torque; but you are driving the spindle through a comparatively small toothed belt. What about backlash in the belt drive and possible belt stretch ?   Is this a real or imaginary problem ?

Regards

Mike
Title: Re: To the dark side CNC
Post by: jadge on August 12, 2015, 12:12:32 PM
Stuart: If the learning curve goes over the vertical that's good, as you're then on the way back to horizontal! Despite a number of CAM/CNC issues with the parts shown, the majority of the time taken was in the actual design, not related to the machining at all. I'll be interested to see what you do regarding tooling plates. Early on I bought a large (20" x 14" x 1"), and expensive, piece of ground aluminium jig plate. I designed a tooling plate with lots of tapped holes, and reamed holes for dowel pins. So far I haven't got around to actually making it. For smallish parts I use a machine vice. A lot of parts rest direct on the machine table, and for those where I am profiling edges I use a sacrificial lump of ordinary aluminium plate.

Chuck: The helical gears look good. As a result of discussions on another forum I am looking at the mathematics of helical gears. I'd be interested in knowing a bit more about the setup used to machine them. Did you use an involute cutter, set over at the helix angle, similar to using a universal mill and dividing head, or a small slot drill making a series of passes for each tooth? If you used an involute cutter how did you calculate the equivalent number of teeth used to select the cutter? If you used a slot drill how did you model and/or calculate the tooth shape?

I'm a bit confused about the use of the 4th axis for thread milling. Some while ago I bought a couple of thread milling cutters from Maritool, but haven't had a chance to use them yet. However, I was under the impression that I could use the mill in 3-axis mode to generate the necessary helix for cutting both internal and external threads. Have I misunderstood?

Andrew
Title: Re: To the dark side CNC
Post by: kvom on August 12, 2015, 01:13:30 PM
I did quite a bit of thread milling for the studs on the Joy engine.  Cutter in normal Z directions with spiral in XY.  The only reason to use a setup like Chuck's is if the mill is only 2-axis, or just to show it can be done that way.  For feeds and speeds I've been using the calculations discussed on the Harveytools website.  I have two single-point cutters.  The smaller one is 8-32 and can cut threads to 56 tpi.  The larger is 1/4 and can cut to 40 tpi.  Got them from carbide depot.  I recently bought a third cutter from them to cut 1/8-NPT  and 1/16-NPT, both of which are 27 tpi.  This one has 10 teeth and cuts a full thread in a single turn.  I'll use this for piping on engines (nipples, unions, plugs).

I do all my CNC milling using the vise, with ad-hoc fixturing, soft jaws, etc.
Title: Re: To the dark side CNC
Post by: jadge on August 12, 2015, 03:05:30 PM
kvom: Thanks for the confirmation that I wasn't losing my marbles. I guess the 4th axis technique could be useful when cutting coarse, or special form, threads like the worms I showed earlier.

Despite having a relatively large vice (Kurt D688) I find it simpler to clamp many parts to the table or sub-plates when the parts are too big for the vice or need full depth profiling, like these:

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_Parts.JPG)

Andrew
Title: Re: To the dark side CNC
Post by: Dave Otto on August 12, 2015, 03:48:21 PM
Your parts look real nice Andrew; what type of machine do you have?

Dave
Title: Re: To the dark side CNC
Post by: Hugh Currin on August 12, 2015, 04:49:32 PM
I have to find the time to build a 4th axis. I believe my driver board has four slots, just need a 4th gecko, and LinuxCNC will handle a 4th axis. I was thinking of using a two belt drive system for better torque and resolution. Maybe build the spindle for 5C collets since I have a set  of those. It makes the whole thing large though. Alternately I may use a Sherline spindle to build a 4th axis from. But I still need to find the time.

I think a 4th axis would be handy for cutting gears. It should be feasible to build a hob and generate spur and helical gears with a 4th axis. It's likely too many steps for be feasible by hand but with a CNC...

I believe timing belts have near zero backlash. My mills X,Y,Z conversion mechanicals have belt drives which work well. Just tighten them down well.

I just looked at Fusion but can't use it. I run Linux and it's only for Windoz and Mac. I have been able to get CamBam running under Linux and really like it. I don't think it's easily adaptable to Mac though.

Thanks.

Hugh
Title: Re: To the dark side CNC
Post by: Tennessee Whiskey on August 12, 2015, 05:19:25 PM
I have to admit,  as one who still hasn't figured out all the goodies included in my DRO, I find all of this quite fascinating

Cletus
Title: Re: To the dark side CNC
Post by: MMan on August 12, 2015, 05:27:32 PM
I have just had a first go with Fusion 360. Previously I have done 2D with Draftsight and CamBam so I was keen to see how Fusion worked for a sculpted part.

Here is my first part as a rendering and as a first cut. I found building the model quite easy (normal software caveats apply) and rendering is just icing on the cake. CAM for 3D I think I have more to learn but the software does what it says it will and no surprises.

You can clearly see the track of the 6mm ball ended cutter even after 3 operations. I think I either need a tighter finishing pass for the near horizontal surfaces or perhaps use a bull nose cutter rather than a ball, to leave small steps rather than grooves. Anyway a first step and one I am quite pleased with, the part is to be used in a dog guard in the car.

Mman
Title: Re: To the dark side CNC
Post by: Vixen on August 12, 2015, 05:36:13 PM
I built in an extra 4th axis microstepping drive module when I updated my Austrian EMCO (not ENCO) F1 mill last year. My DeskNC software can handle the 4th axis.

My first attempt at a 4th axis table was to fit a 1.8 Nm stepper as a direct drive to a small and very low quality 4" rotary table. It sort of worked, I was able to index spur gears. The problem was backlash in the rotary table's worm gears. The gear blank would move within the limits of the backlash due to the vibration of the cutting forces. There was no easy way to clamp the two halves of the RT other than with a large G clamp.

I am currently thinking about making a second 4th axis unit, based on a redundant EMCO Compac 5 lathe head and spindle. For me, it has the advantage of being able to accept my EMCO 3 and 4 jaw chucks and my EMCO ER25 collet adapter. The neat 4th axis unit made by Chuck Fellows, (posted here yesterday) is just what I had in mind to make.

I planned to use a 200 step 4.0Nm NEMA 23 stepper (that's 550 once/inches) driving through a 6:1 toothed belt reduction, with a 15mm wide 5mm pitch timing belt. Hopefully the timing belt drive will eliminate the backlash problem. My chosen motor has only 1/3 the torque of Chuck's giant stepper so I am a little concerned that my 4.0Nm stepper may not be powerful enough. Do I really need a 11.3Nm (1600 oz/inch) motor like the one Chuck uses? Experience and advice would be appreciated.

Regards

Mike

 
Title: Re: To the dark side CNC
Post by: Vixen on August 12, 2015, 05:59:14 PM
Hi Mman
This is the finish I get when using a 8mm ball cutter on aluminium with 15 thou stepovers between lines of the final pass. Roughing out is done to within 10 thou with much larger stepover distances.

It is a big trade off, reduce the stepover to 10 or 5 or even less and you will have less hand finishing to do with the wet-and-dry, but the machining takes forever. I am not happy about the idea of letting the machine run all night unattended. so I opt for a courser and quicker final pass.

(http://i901.photobucket.com/albums/ac218/v8vixen1/P1040833.jpg)

How close are you to Fareham Hampshire?

Regards

Mike
Title: Re: To the dark side CNC
Post by: MMan on August 12, 2015, 06:13:10 PM
Thanks Mike,

Your step over is still way less than mine at 2mm so I will try reducing it and watch the cutting times, both Fusion and Mach give cutting time estimates (and they seem to agree). I do not trust it to run overnight either - I worry about coming back in the morning and what I might find.

I still have some more investigation to do on creating a 2d profiling operation to separate the piece from the stock (with tabs) and am browsing about in Fusion for something simple.

I am just up the road from Fareham, in Winchester.

Mman.
Title: Re: To the dark side CNC
Post by: Hugh Currin on August 12, 2015, 07:38:45 PM
I have just had a first go with Fusion 360. Previously I have done 2D with Draftsight and CamBam so I was keen to see how Fusion worked for a sculpted part.

Here is my first part as a rendering and as a first cut. I found building the model quite easy (normal software caveats apply) and rendering is just icing on the cake. CAM for 3D I think I have more to learn but the software does what it says it will and no surprises.

You can clearly see the track of the 6mm ball ended cutter even after 3 operations. I think I either need a tighter finishing pass for the near horizontal surfaces or perhaps use a bull nose cutter rather than a ball, to leave small steps rather than grooves. Anyway a first step and one I am quite pleased with, the part is to be used in a dog guard in the car.

Mman

I suspect a bull nose cutter will only cause problems, unless the CAM program can accommodate one. If the CAM part is there a bull nose sould work well. The larger the ball nose cutter the better (provided it can get into the corners).

There is a calculation to give scallop height (extra material left above surface) for a give ball nose cutter diameter and step over (along surface). I googled this and found several calculators but not the base equations. This would likely give a relative indication, half the step over decreases the scallop by X%, but need some real world experience to know what the numbers mean. If I find the calc I'll send it on to the list.

Thanks.

Hugh
Title: Re: To the dark side CNC
Post by: cfellows on August 12, 2015, 09:10:33 PM
Hello Chuck

I like your 4th axis set-up. It has got me excited and thinking about making one for myself.

I see you are using a HUGE stepper motor and I can understand the need for plenty of torque; but you are driving the spindle through a comparatively small toothed belt. What about backlash in the belt drive and possible belt stretch ?   Is this a real or imaginary problem ?

Regards

Mike

Mike, the stepper motor isn't that big.  It's a NEMA23, I think under 200 oz in.  There is no measurable backlash or belt stretch that I can see.  I also use timing belts on my milling machine steppers.  The motors are NEMA23, 425 oz in torque.  The backlash on both X & Y is about .001" and I think that is mostly in the ball screws.  So, in my experience at least, backlash issues with timing belts are mostly a myth.
Title: Re: To the dark side CNC
Post by: cfellows on August 12, 2015, 09:16:58 PM
Stuart: If the learning curve goes over the vertical that's good, as you're then on the way back to horizontal! Despite a number of CAM/CNC issues with the parts shown, the majority of the time taken was in the actual design, not related to the machining at all. I'll be interested to see what you do regarding tooling plates. Early on I bought a large (20" x 14" x 1"), and expensive, piece of ground aluminium jig plate. I designed a tooling plate with lots of tapped holes, and reamed holes for dowel pins. So far I haven't got around to actually making it. For smallish parts I use a machine vice. A lot of parts rest direct on the machine table, and for those where I am profiling edges I use a sacrificial lump of ordinary aluminium plate.

Chuck: The helical gears look good. As a result of discussions on another forum I am looking at the mathematics of helical gears. I'd be interested in knowing a bit more about the setup used to machine them. Did you use an involute cutter, set over at the helix angle, similar to using a universal mill and dividing head, or a small slot drill making a series of passes for each tooth? If you used an involute cutter how did you calculate the equivalent number of teeth used to select the cutter? If you used a slot drill how did you model and/or calculate the tooth shape?

I'm a bit confused about the use of the 4th axis for thread milling. Some while ago I bought a couple of thread milling cutters from Maritool, but haven't had a chance to use them yet. However, I was under the impression that I could use the mill in 3-axis mode to generate the necessary helix for cutting both internal and external threads. Have I misunderstood?

Andrew

Andrew, I did use an involute cutter set at the helix angle for cutting the helical gear.  I've attached an excel spreadsheet that has a lot of the tables and math used for helical gears.

My thread milling operation used a 60 degree milling cutter, not an actual thread milling cutter.  I learned later that there is an easier way to cut threads without a 4th axis, also using just a 60 degree milling cutter.  Of course, for internal thread, it may require a really small cutter, so a thread mill might be better.  I have a friend that runs a local machine shop and he swears by thread milling, but I have no experience with them.
Title: Re: To the dark side CNC
Post by: jadge on August 12, 2015, 09:22:52 PM
Dave: I have a Tormach PCNC1100 Series 2, imported into the UK from the US. I bought the mill and the 4th axis kit with 8" table together, as I figured that shipping the rotary table at the same time as the mill wouldn't be a huge extra cost. Before buying I spent a lot of time looking at various options including hobby machines, a new Haas, and secondhand commercial CNC mills like Bridgeports. The Haas was out of my price bracket, especially when including 'essential' items that were priced as options. The larger Bridgeport CNC mills wouldn't fit in my workshop, and I hated the idea of having to debug 1980s electonics if there were problems.  :ThumbsDown: The Tormach seemed a good compromise; capable of handling the size of parts I knew I would be machining, a 4th axis was available, and it would cope with tougher materials. I was also impressed by the no nonsense design notes and white papers on the Tormach website. Overall I have been very pleased with my purchase.

The calculations for ridge height versus stepover for a ball nose mill should be simple geometry, although it is built in to my CAM program so I have never actually sat down and done the maths. The finish cut on the bevel pinion shown previously was done with a 4mm ball nose cutter and a step over of 0.1mm (4 thou). Total machining time was 2½ hours, including all the roughing. As another example here is a spline cutter machined from gauge plate using only a 6mm ball nose cutter:

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_Spline_Cutter_MEM.JPG)

Stepover on the finishing cut was 0.4mm (16 thou) and that gave a pretty good finish; although the ridges can be seen they can't be felt. Total machining time was about 4 hours.

I wonder what speeds and feeds people are running at? For the bevel pinion I was running at 5000 rpm and 400mm/min, and for the spline cutter 3000rpm and 150mm/min, both cutters being 3 flute uncoated carbide.

Andrew
Title: Re: To the dark side CNC
Post by: Vixen on August 12, 2015, 09:35:16 PM
Chuck

Now you have me confused. You said in your reply  'the stepper motor isn't that big.  It's a NEMA23, I think under 200 oz in' . 

This morning I found your utube video https://www.youtube.com/watch?v=1YeG42yBHwo which shows a massive Nema 34 1600 oz/inch stepper.

What stepper do you use for your helical gear work?

Cheers

Mike
Title: Re: To the dark side CNC
Post by: Hugh Currin on August 13, 2015, 12:46:04 AM
The calculations for ridge height versus stepover for a ball nose mill should be simple geometry, although it is built in to my CAM program so I have never actually sat down and done the maths.

Andrew

It was simpler than I thought. Checks against at least one on line calculator.

(http://www.currin.us/MEM/scallop.jpg)

Thanks.

Hugh
Title: Re: To the dark side CNC
Post by: Dave Otto on August 13, 2015, 01:12:09 AM
Thanks Andrew

Someday I would like to have a more capable CNC mill in the home shop. Mine is a converted Bridgeport clone, knee mill that I converted myself. I have been pretty happy with it so far but the lack of quill travel leaves a lot to be desired. My machine at work is much more capable and I'm welcome to use it after hours and on weekends which is nice.

I did include a 4th servo amp in the box and all the connectors to add a 4th down the road; I just need to figure out what I want to build and start collecting parts.

Dave

Title: Re: To the dark side CNC
Post by: Dave Otto on August 13, 2015, 01:21:14 AM
I have just had a first go with Fusion 360. Previously I have done 2D with Draftsight and CamBam so I was keen to see how Fusion worked for a sculpted part.

Here is my first part as a rendering and as a first cut. I found building the model quite easy (normal software caveats apply) and rendering is just icing on the cake. CAM for 3D I think I have more to learn but the software does what it says it will and no surprises.

You can clearly see the track of the 6mm ball ended cutter even after 3 operations. I think I either need a tighter finishing pass for the near horizontal surfaces or perhaps use a bull nose cutter rather than a ball, to leave small steps rather than grooves. Anyway a first step and one I am quite pleased with, the part is to be used in a dog guard in the car.

Mman

Mman

When doing surfacing tool paths most CAM programs will let you leave a stock allowance for cleanup on the finish pass. Depending on the material being cut I will leave anywhere from .002" to .02" or more. Also there usually a setting for the tolerance; for the roughing passes I will set it at .001" and .0001" for the finish.

It appears that your roughing passes are cutting deeper than your finish pass; this could be for a number of reasons. tool flex, or maybe backlash in Z. I would start with trying to leave more for the clean up pass.

Its great to see some CNC discussions here on the MEM forum.

Dave 
Title: Re: To the dark side CNC
Post by: jadge on August 13, 2015, 09:30:47 AM
Chuck: Thanks for the spreadsheet, it is pretty neat. I note that the spreadsheet uses the standard divide by cos of the helix angle cubed to get the equivalent number of teeth to select a cutter. It is fairly simple to derive the equation from first principles using the radius of curvature of an ellipse. However, what confuses me is that some sources, eg, Machinery's Handbook, give a revised formula with an additional term involving the cutter pitch diameter and normal DP. I'm not sure how this extra term arises. Apparently it is most useful for gears with high helix angles and low tooth count. That seems to apply to one of your helical gears, but presumably the gears meshed without any problems?

I have also seen another variation involving dividing the actual number of teeth by the square of the cosine of the helix angle and the sine of the helix angle. The example given was for 45° which of course works as sin(45) = cos(45). However, for zero helix angle, ie, a spur gear, the equation blows up as sin(0) = 0. There is also an equation involving the tangent of the helix angle and the helix angle itself, but I haven't had time to look into that yet.

Andrew
Title: Re: To the dark side CNC
Post by: cfellows on August 13, 2015, 02:47:34 PM
Chuck

Now you have me confused. You said in your reply  'the stepper motor isn't that big.  It's a NEMA23, I think under 200 oz in' . 

What stepper do you use for your helical gear work?

Cheers

Mike

Sorry Mike, the dividing head in this video is the second 4th axis I built.  It has a NEMA34, 1600 oz in stepper.  I rarely use it because it is so big and harder to mount in the mill.  The original 4th axis, which I use most of the time, has the NEMA23 stepper.  The spindle is an ER20 Collet chuck with a 3/4" spindle diameter.  Here is a video of it in action.

https://www.youtube.com/watch?v=L18a_wfaRBE

Title: Re: To the dark side CNC
Post by: cfellows on August 13, 2015, 02:51:31 PM
Chuck: Thanks for the spreadsheet, it is pretty neat. I note that the spreadsheet uses the standard divide by cos of the helix angle cubed to get the equivalent number of teeth to select a cutter. It is fairly simple to derive the equation from first principles using the radius of curvature of an ellipse. However, what confuses me is that some sources, eg, Machinery's Handbook, give a revised formula with an additional term involving the cutter pitch diameter and normal DP. I'm not sure how this extra term arises. Apparently it is most useful for gears with high helix angles and low tooth count. That seems to apply to one of your helical gears, but presumably the gears meshed without any problems?

I have also seen another variation involving dividing the actual number of teeth by the square of the cosine of the helix angle and the sine of the helix angle. The example given was for 45° which of course works as sin(45) = cos(45). However, for zero helix angle, ie, a spur gear, the equation blows up as sin(0) = 0. There is also an equation involving the tangent of the helix angle and the helix angle itself, but I haven't had time to look into that yet.

Andrew

My spur gears seem to mesh just fine for model engine work.  Didn't realize there was more math for special cases...
Title: Re: To the dark side CNC
Post by: Vixen on August 13, 2015, 03:50:57 PM
Hello Chuck

Thanks for taking the time to explain about your two different 4th axis units.

I have seen adverts for some quite low torque 4th axis units originating from China, they are described as suitable for engraving (wood plastic?). When I saw your massive 1600 oz/inch motor, I was worried that that sort of torque was what was required for metal bashing. You have set my mind at ease, now I know you normally use the much smaller 200 oz/inch motor. I guess what we make is often governed by what we find in the 'come in handy' box.

I now feel comfortable that when I use of a microstep driver on a 200 step 3.0Nm NEMA 24 stepper (400 once/inches) through a 3.6:1 toothed belt reduction, with a 15mm wide, 5mm pitch, timing belt, it should be more than adequate. That should give a basic 0.5 degrees per step, then there is the microstepping.

I may start a new topic when I have made some progress.

Thanks again

Mike
Title: Re: To the dark side CNC
Post by: Hugh Currin on August 13, 2015, 06:33:26 PM
You have set my mind at ease, now I know you normally use the much smaller 200 oz/inch motor.

Mike

Mike: Well, let me attempt to dash that comfortable feeling.

I think comparing the holding torque for a lead screw to that needed for a 4th axis shows the 4th axis drive needs considerable torque. The lead screw is very good as a gear reduction and in lowering needed motor torque. I ran a calc to quantify this as:

(http://www.currin.us/MEM/FourthAxis-1.jpg)

(http://www.currin.us/MEM/FourthAxis-2.jpg)

This is leading me to use a double step timing belt drive for a 4th axis. I can't see how to get reasonable reduction otherwise. There is a "commercial" 4th axis by Simpson that uses a double reduction. Actually configurable for double belt, 4th axis, or single belt, turning. This video (https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRxqFQoTCJmDu-bHpscCFcyaiAodnRMA8A&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DsC2urdg_bqg&ei=yNDMVZn_O8y1ogSdp4CADw&bvm=bv.99804247,d.cGU&psig=AFQjCNFXLmy7gZjBmSZNHPW6taiJfNoMXg&ust=1439572511767711) giving an idea how it works. I like the concept but can't afford the item.

If anyone sees holes in this calc please let me  know. It does assume a worst case cut, pushing sideways. But I have not yet built one, and Chuck is having good luck with his. I'd sure like it if I was proven wrong and a single reduction was optimum.

A little off topic, but the 4th axis came up and I have an interest. Thanks for bearing with the diversion.

Thanks.

Hugh

Title: Re: To the dark side CNC
Post by: Vixen on August 13, 2015, 08:54:13 PM
Hello Hugh.

An interesting discussion.

I agree, for the linear axes and a given cutter load, the stepper torque requirement remains constant and is proportional to the ball contact diameter and the lead angle of the ball screw. The ball screw geometry was fixed during design.

For the 4th axis, given the same cutter load, the stepper torque requirement is a variable. It depends on the diameter where the cut is made and the angle at which it is applied. Clearly large diameter workpieces and radial cuts at 90 degrees to axis will generate the highest loads which require higher holding/driving  torque. They could be many times larger than that of a ball screw in one of the linear axes.

Fortunately the cutting force is under the control of the programmer. Reducing the depth of cut, the stepover and the feed rate will all reduce the cutter force. The torque required to resist longitudinal cuts of a spur gear will be significantly less than the largely radial cuts required for a worm wheel. It is for the programmer to consider the geometry of the required work and program the cutter parameters accordingly. Nothing changes, it has always been that way.

Yes, you can always use a bigger motor and higher belt reduction ratios to increase the holding/ rotating torque. 'The Simpson' offers the option to use one or more gear reduction ratios to match the job.

The demo video was rather misleading. There is no way that long tube held at one end only in the 3 jaw could resist much in the way of a side load, but then, the marker pen used to draw the fairy would not have produced much load anyway. You can draw as fast as the machine will move.

I still have that comfortable feeling knowing that Chuck's 4th axis unit works. He clearly programs the cutter parameters within the limitations of the machinery. We are dealing with model engineering not large scale industrial production, we can afford to slow down and play a little.

Regards

Mike


Title: Re: To the dark side CNC
Post by: Hugh Currin on August 13, 2015, 09:27:57 PM
I still have that comfortable feeling knowing that Chuck's 4th axis unit works.

Mike

Real world performance trumps math every time. It's a good argument that Chuck's 4th axis works well. But still the analysis give me pause and I may well do something like the Simpson when I get around to building one.

Thanks.

Hugh
Title: Re: To the dark side CNC
Post by: Vixen on August 13, 2015, 09:46:52 PM
Hello Hugh

Interesting discussion.

Practical machinists learn to live within their machine's capabilities.

The Simpson, one or two belt reduction option is a neat trick and one that can be added very easily, just add the second belt when required.

Have you checked the lead v diameter ratio for real world ball leadscrews? The helix angle, theta, can be 45 degrees. I can push my x and y axis around when the power is removed, they do not lock like a screw thread.

Regards

Mike
Title: Re: To the dark side CNC
Post by: jadge on August 13, 2015, 10:15:18 PM
It is interesting that my (commercial) 4th axis drive has a stepper motor directly connected to a worm and worm wheel, as per most manual rotary tables. While that limits the maximum rotary table speed to about 5 rpm it has the advantage that the cutting forces are not directly opposed by the motor holding torque but by the worm and worm wheel. It never occurred to me to reduce cutting parameters when using the rotary table. When I roughed out the worm shown previously I used speeds, feeds and DOC that I would have used in 3-axis mode for the selected cutter.

It also means that the resolution (if not the accuracy) per step of the motor is about 1 minute of arc.

Andrew
Title: Re: To the dark side CNC
Post by: Vixen on August 13, 2015, 10:44:12 PM
Andrew

My first 4th axis unit was also manual rotary table. It was a poor quality thing and I could never get rid of the backlash in the worm and wheel. That is why I am about to make a 4th axis spindle, based on a small lathe headstock. My mill is only a small desk top EMCO F1 so I have learned  from day one. the art of reducing the cutting parameters to live within my machines capabilities, I can barely believe the feeds and speeds of your Tormach working gauge plate.

Are you far from Fareham in Hampshire?

Regards

Mike
Title: Re: To the dark side CNC
Post by: jadge on August 14, 2015, 11:46:16 AM
Mike: Here's a general shot of my 4th axis rotary table and tailstock. It's not as rusty as it looks, just a consequence of the camera settings:

(http://lister-engine.com/coppermine/albums/userpics/10022/normal_4th_Axis.JPG)

My CNC mill is nominally the same horsepower as my manual Bridgeport. So my expectations were that it would be comparable in terms of removal rates, with some caveats of course. The CNC spindle speed is much higher than the Bridgeport, so I tend to run smaller cutters at faster speeds than on the Bridgeport. This also helps as the CNC mill is not as heavy, and hence rigid, as the Bridgeport. The other main caveat is the CNC spindle is driven by a 3-phase motor from a VFD, whereas the Bridgeport is a 3-phase motor via a varispeed belt drive. So the Bridgeport is essentially constant power, whereas the CNC spindle is constant torque (not constant power) below the base speed of the motor. I've made a note of what rpm corresponds to base speed and take this into account when selecting cutting parameters.

I live near Cambridge, the closest I get to Fareham is Horndean as I have an uncle who lives there. However, a couple of times a year I go to a traction engine meeting south of Reading, which is probably a bit over half way.

Andrew
Title: Re: To the dark side CNC
Post by: MMan on August 14, 2015, 07:35:03 PM
Thanks All,

I have changed my milling operations to be a roughing operation (parallel), leaving about 0.5mm. Followed by a scallop op to finish the shallow surfaces and a contour to finish the sides, both with small step overs. I have also changed cutter to a bull nose, although it will probably not make as much difference now the step overs are reduced. Cutting time is still not too bad at 2 hours.

I have added one more op which is a 2d operation to separate the work from the stock. This needed tabs and the only op that can create tabs is a 2D Contour which is much like a Profile in CamBam. In order to use this I needed a 2D outline for it to follow. You can create a 2D sketch from a 3D body with Project in the Sketch menu. The sketch is then visible in CAM and can be selected to create an outline. This might be a useful way of getting at 2D operations for other reasons, don't ask me what for but I am new to 3D and not giving up on 2D yet.

I will post a pic once I get some more workshop time to have another go. This could take a while, our baby daughter takes most of my time at the moment,

All the best Mman.
Title: Re: To the dark side CNC
Post by: Dave Otto on August 15, 2015, 01:10:02 AM
Nothing wrong with extracting 2D geometry from your solid to be used in tool paths; I do it routinely both at home and the day job. Sometimes with a CAM program you have to go after it with a big hammer to get it to do what you want.  :lolb:

Dave
Title: Re: To the dark side CNC
Post by: MMan on August 25, 2015, 12:38:00 AM
Thanks Dave.

I got some time today and so recut with a bullnose cutter and the modified CAM settings, including the 2d operation. It is a whole lot better. The only thing I would change if I was to do it again is there are two finishing passes, one for the near horizontal and one for the near vertical and they overlap leaving me with patterning. There is probably a control for it but I did not see it (or understand its use).

For this application the finish is fine (the previous version would have been too, except I needed the 2d op to cut down and through). A quick rub with a hand pad and it will be perfect.

Mman
Title: Re: To the dark side CNC
Post by: Vixen on August 25, 2015, 10:14:33 AM
Mman, That looks like a fine piece of machining. 
When the surface is bright and shiny and newly cut it, always seems to emphasise the scollops. Sometimes you can see them but not feel them. Give it a rub over with a Scotchbrite pad and it will look completely different, much smoother.
It is always a trade off when it comes to the finishing pass, you can half the final step over distance to try and improve the surface finish at the cost of doubling the machining time. Even die makers need to hand finish to achieve the final mirror smooth surface finish.
Title: Re: To the dark side CNC
Post by: MMan on August 25, 2015, 01:15:27 PM
Thanks Mike,

It certainly shows me that Fusion 360 works and that I can start moving from 2D to 3D.

Mman.
Title: Re: To the dark side CNC
Post by: kvom on August 25, 2015, 01:54:53 PM
Thanks Mike,

It certainly shows me that Fusion 360 works and that I can start moving from 2D to 3D.

Mman.

Each has its place, and it's usually wrong to do 3D machining where 2D will work.  3D modeling works for both.
Title: Re: To the dark side CNC
Post by: MMan on August 25, 2015, 05:45:30 PM
Hi Kvom,

I completely agree, I was very relieved when I found the 2D operations in the CAM section.

All a question of picking the right tool for the job - much like the CNC vs. manual discussions. Both have their pros and cons and in both cases we have to work out how to use them to make what we want.

All the best,

Mman.
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