Pros and Cons of home shop CNC

[Vixen]

For me its a bit like knitting: I started learning to knit by hand. In my late teens I brought a knitting machine. Yes there was the "programming" but having made possibly 20 or so jumpers on the machine I just found it boring. Knocking out jumpers did nothing for me. Years later all I do is hand knitting and I threw the knitting machine in the skip. The challenge for me is the hand skill, I also by commercial knitted jumpers from the shops - It is cheaper to buy a commercial jumper than to buy wool to knit one.

Jo

Hello Jo,

Do you remember you knitted me a Fowler Ploughing Engine jumper on that knitting machine. But my, that was a long, long time ago.

Mmmmm!! Jo in her late teens 



Thanks again

Mike

[Jo]

I do 

My latest speciality is hand knitted socks: I could do some with ploughing engines round them 

Jo

[Jo]

Mmmmm!! Jo in her late teens 

Its been down hill since then   

Jo

[gbritnell]

 Actually I think having a CNC mill is very beneficial, if, you can afford one that will do what you need, if, you are familiar with a solid modeling program to make parts, if, you are somewhat tech literate to understand the functionality of the machine itself and it's connection with the computer, if, you can afford all the tooling (end mill holders, collets, cutters etc.) You think making fixtures to hold parts for manual machining is a pain well a CNC mill will only cut a part in the Z direction (I know it moves in X and Y also) just like manual machining so if the part has details on the sides or bottom then you have to use a fixture or tooling setup to do those sides. It's not just pop the part into the machine and wait for the finished product to come out. Some CNC mills don't have automatic tool changers so at the end of a cutting cycle the operator has to manually change the tools.

 Now don't take the preceding paragraph as me being against having or using a CNC mill. On the contrary! I would love to have one but do I really need one? No. To make one of two engines or models per year certainly doesn't justify having a CNC mill. Lord knows I spend enough time on the computer making 3d models for my 3d printer and 2d drawings for everything I make.

 Most of the long time members on the forum know me and my work. The one model I made (T-5 transmission) took hours and hours of manual machining and hand work to complete the housings alone. I would have relished having a CNC mill to do the work but after the parts were made how long would it have been before it was put to use again. I do a lot more machining on my manual lathe and mill in the course of day than I would on a CNC machine.

[Alyn Foundry]

After running with my old Gal for nigh on 40 years now. I find manual machining almost second nature. I rarely need to measure when roughing, I know my machine so well. As Jo has pointed out there’s nothing interesting about watching a machine doing the work that you could do.

However, Jason has provided me with several patterns made using the CNC process. They have been absolutely perfect in every way. I now have a different view on the use of CNC/CAD where just a one off is required.

In my opinion a casting provides the end user with the means to make something that works with minimal wastage. The profile remains a constant particularly in the area of marketing “ true to scale “ models.

Needless to say at my age I won’t be going over to what Jason refers to as the Dark side but I can see its virtues. Attached a couple of photos of some of Jason’s CNC/CAD patterns that he made last year. Along with the machined castings.

   Graham.

[Jasonb]

For me its a bit like knitting: I started learning to knit by hand. In my late teens I brought a knitting machine. Yes there was the "programming" but having made possibly 20 or so jumpers on the machine I just found it boring. Knocking out jumpers did nothing for me. Years later all I do is hand knitting and I threw the knitting machine in the skip. The challenge for me is the hand skill, I also by commercial knitted jumpers from the shops - It is cheaper to buy a commercial jumper than to buy wool to knit one.

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CNC embroidery machine  I don't think I could justify one of those (yet).

Jo

Strange Jo only a couple of days ago you seemed interested in CNC embroidery yet now you don't seen to want to let a machine do some of the work

[Jasonb]

Actually I think having a CNC mill is very beneficial, if, you can afford one that will do what you need, if, you are familiar with a solid modeling program to make parts, if, you are somewhat tech literate to understand the functionality of the machine itself and it's connection with the computer, if, you can afford all the tooling (end mill holders, collets, cutters etc.) You think making fixtures to hold parts for manual machining is a pain well a CNC mill will only cut a part in the Z direction (I know it moves in X and Y also) just like manual machining so if the part has details on the sides or bottom then you have to use a fixture or tooling setup to do those sides. It's not just pop the part into the machine and wait for the finished product to come out. Some CNC mills don't have automatic tool changers so at the end of a cutting cycle the operator has to manually change the tools.

I suppose it depends on the CNC but I had an R8 spindle manual mill before getting the CNC which is also R8 so did not have to buy anything in the way of tooling and was able to start making parts with the tooling and HSS cutters that I had. I've since added some Carbide cutters t make better use of the higher spindle speed  better clear the swarf and a smaller ER16 collet holder better clear the swarf so that need not be a con.

There is no more need for fixturing between an manual mill and 3 axis CNC as both really only cut in Z as you say. When I do use fixture plates I can use the 3D part to pick up the location of tapped holes for holding the part down or can cut nesting jaws to hold odd shaped work for second ops so may be even a pro rather than a con.

Quiet a few here seem to have a 4th axis added so on smaller parts you can hold a bit of stock in the 4th axis chuck and have it index the part round in 90deg steps so you can get at it from all 4 sides to do all the roughing and then round again for finishing and maybe round again to add holes etc and not once have you had to disturb the hold of the work so it will be in the exact same place for every operation, I'd say that is a pro. Interestingly I have been swapping a few e-mails with someone who wants to make a 1/3rd scale Galloway but as castings are hard to get he intends to make from solid with his Tormach, the bed casting will be done using the 4th axis so all areas can be reached and no need for excessively long cutters to get at the deeper recesses. Or you could go the whole hog and get a little desktop Pocket NC machine the gives you 5-axis all in the single set up

I doubt many with home machines have autochangers, some will have quick change others just get on fine with changing tools as needed which is no different to changing tools on a manual mill so neither a pro or con. Same for needing to be there to change tools you have to do that on the manual mill as well but the big advantage of the CNC is you don't have to be there while it is cutting like you do with  a manual machine so can be making another part on another machine or doing something completely different got to be a pro again.

[Jasonb]

One issue is having access to a decent CAD / CAM program.  That is where there's lots of time savings to be had as an amateur that doesn't use it frequently.  I'm sure that if I used it more I'd learn more tricks to be faster in programming but for now I'm pretty slow.  Also, not to turn this thread into a what software to use discussion but I'm leaning towards buying Alibre Workshop bundle (Alibre Atom and MeshCam) at the moment as a way of escaping from Fusion360 ever dwindling free offering. It looks like the 3-axis CAM (Meshcam) is really easy – so hopefully that makes it easier to get off the PC and hop into the shop to make stuff.

I did get a trial of Meshcam with a view to getting it to run alongside my Alibre Pro but found it quite basic and lacking many features that F360 has. It is more aimed at the "maker" with a gantry type machine working in various materials and only the occasional but of metal. It's limited if you want to do 3D work as it does not have much in the way of finishing path options except parallel and I recently read of someone using to to make a part out of some round stock and they said Meshcam only works with square or rectangular stock (sheet on a gantry machine) so there was a lot of air cutting which made for a very extended run time. F360 will happily accept square, rectangular, or round stock and you can also model the stock if it's an odd shape for example if the part is L shaped you can save time by sawing out most of the waste and then tell F360 it is working with a rough cut L shape and it does not cut any more material than needed. Not much in the way of adaptive tool paths either

It was quite easy to use but there is nowhere near as many features to learn how to use.

[Jo]

CNC embroidery machine  I don't think I could justify one of those (yet).

Strange Jo only a couple of days ago you seemed interested in CNC embroidery yet now you don't seen to want to let a machine do some of the work

I am waiting to inherit one  but I would prefer it is a long way in my future 

Jo

[springcrocus]

Jo,

Just to whet your appetite...



Regards, Steve

[Alex]

3D and 4th axis.

MikeR - CamBam can do 3D profiles. I have played around with it, but currently, no need for it in what I'm doing, but it is there if required. Have Meshcam with the Alibre Atom3D bundle, but other than starting it up, I thought that CamBam was better. Not much to go on, I know. Alibre Atom3D - there was (and still is) no room for a windows box in the office as work/play is macOS and Linux, and one day I tried to run Atom3D in a virtual machine on Linux, and it locked the license. I installed FreeCAD and have not looked at Atom3D since. (yes, a good soul got the license unlocked, but by that time the Windows box was in storage and desk re-arranged) I'm sure Alibre Atom3D is great, but change the hardware, and watch out...

For 4th axis machining, I used CamBam with added GCODE files, simply to flip the rotary around. These little links on a Shay locomotive go from the reversing lever to the reversing arm on the engine, and are pretty well hidden when complete. Here are some photos of how I did it. It was really nice to see the parts drop off, with minimal finishing.

The biggest issue I had was taking the time to zero everything, I wanted to see how things went! I ended up shining the parts shown up, and they look great.

[steamer]

Actually I think having a CNC mill is very beneficial, if, you can afford one that will do what you need, if, you are familiar with a solid modeling program to make parts, if, you are somewhat tech literate to understand the functionality of the machine itself and it's connection with the computer, if, you can afford all the tooling (end mill holders, collets, cutters etc.) You think making fixtures to hold parts for manual machining is a pain well a CNC mill will only cut a part in the Z direction (I know it moves in X and Y also) just like manual machining so if the part has details on the sides or bottom then you have to use a fixture or tooling setup to do those sides. It's not just pop the part into the machine and wait for the finished product to come out. Some CNC mills don't have automatic tool changers so at the end of a cutting cycle the operator has to manually change the tools.

 Now don't take the preceding paragraph as me being against having or using a CNC mill. On the contrary! I would love to have one but do I really need one? No. To make one of two engines or models per year certainly doesn't justify having a CNC mill. Lord knows I spend enough time on the computer making 3d models for my 3d printer and 2d drawings for everything I make.

 Most of the long time members on the forum know me and my work. The one model I made (T-5 transmission) took hours and hours of manual machining and hand work to complete the housings alone. I would have relished having a CNC mill to do the work but after the parts were made how long would it have been before it was put to use again. I do a lot more machining on my manual lathe and mill in the course of day than I would on a CNC machine.

George Im one of your biggest fans!   I am always in awe of your work, since long before this forum started....

I've enjoyed my fairly new foree into CNC.    I've designed many CNC machines and parts of machines for Moore and Milacron, but I've always run manuals in my home shop....but I got the opportunity to get a small CNC at auction...and knowing the only person who ever ran it.......ME......ME advised ME to put in a nice juicy low ball bid and maybe I'd win.....and I did!    Otherwise I wouldnt have sprung for the cash it would have taken to get it....no way..

That said..  There are some economies of CNC.     While a dividing head is still a good thing to have   or a 4th axis..... I have not needed a rotary table...and I sold mine when I sold my last mill.....and I don't miss it ....I can engrave neatly, instead of using punches...which I never seem to get aligned no matter what I do.   Fixturing although necessary, I find to be very easy and intuitive with little more than a plate stuffed in a vise, fly cut it flat and machine what I need to hold the part, and with it anything is possible....as such ....compared to a manual mill, which I've run for near 30 years or so...I find processing parts to be easier,  especially in any quantity over say 2....With model engine work,  I'm always making some sort of fixture to hold something, and in general that doesn't change with CNC...other than avoiding rotary table work.     monotonies jobs....Like a index plate ...are easy on CNC...and while it's running, I'm over running my lathe...
I don't think it will make a better engine, but I do enjoy programming it, I find that a rewarding challenge.   It also allows me the opportunity to do something really complex in the 3D space....that I know I couldn't pull off with step off tables,   My bench vise is an example of that.    Hewn from billet....   I know I don't have the time to do that manually...my shop time is pretty limited, and time pressures are a plenty.   It's let me expand my project list to what I would never think of doing before ....and honestly, I think I spend less on tooling with CNC now than I did on tooling with a manual    there was always a need for some other piece of tooling, special cutters.........and they always seems to be expensive in time or money....

Getting acquainted with the conversational aspect of programming is very helpful in saving time on 1 pieces runs......without getting into CAM.....which is how I program most jobs.   

I use Fusion 360....which I admit is limited on the CAD side, but pretty powerful on the CAM side.....this coming from a guy who started his Engineering career on the drafting boards almost 40 years ago.....

Dave

[FKreider]

I am blessed (and cursed) with adequate shop space to have "full size" machinery. In the region of the USA that I am located many commercial machine shops have gone out of business and as a result some older CNC machinery can be had at very reasonable prices.

I started out with a manual knee mill (without a DRO) and a manual 14" toolroom lathe. Just about two years ago I sold the fully-manual mill and upgraded to a 1994 Kent USA knee mill with a 2-axis Mitutoyo CNC control on it. I cant imagine going back to a full manual machine now. I feel that having the 2-axis CNC motion control combined with the traditional "analog" feel of using a manual knee mill makes for a fantastic blend of technology for a home shop machinist. You can easily throw a piece of stock in the vise and square it up using the crank handles and then a few minutes later be using the conversational programming to punch in a simple bolt hole pattern.

That said I also have a small benchtop CNC mill which has no quill or crank handles so its very similar to a modern CNC machining center - you have to jog the table around via the CNC control screen to set your zero point and touch off tools. I also cant imagine just having this machine as a hobbyist because there is no "feel" involved. 

I am also extremely interested in patternmaking and metal casting however I am not a skilled woodworker so I spend all my time in the CAD program designing parts and patterns in 3D and then mostly 3D print them although I also eventually plan to use a CNC router for larger wooden patterns and match plates.

For me its all about a mix of the old school analog technology blended with enough "new" school (even though all my CNC's are from the 90's) to get things done a bit faster.

[Pete49]

The closest I come to cnc machines is 3 3D printers and a small cnc router which I use to make wooden clock gears as using the scroll saw was a bit slow and needed truing. The mill and metal lathes are manual as are the wood lathes. CNC has its uses but as an older generation and self taught computer user some things are beyond my ken. 

[Jasonb]

For those not that familiar with CNC it might be worth explaining a couple of the terms being used such as "Conversational"

There are a number of ways in which the tool can be positioned on the CNC

1- Manually. Some hobby machines have a handle on the motor or still have handwheels, converted machines may also have their handwheels intact so they can be used to move the axis.

2- Jogging. This is probably best likened to using power feeds on the three axis, you just hold down a button or mouse to move the axis, this can be done at variable speeds or in increments the size of which can be altered. There is also the option to enter a "goto" position and twork will move under the spindle to that position. This is mostly used when setting up the work but can be used for simple machining where the constant jog is just like using a power feed.

3- Conversational - Most operating system will have this in some form or wizards that simplify basic tasks such as milling a circle, facing the top of  apart or drilling a hole PCD pattern. Taking the last of those this is virtually the same as entering the details on a DRO except when you press go the work will move rapidly from one position to the other no faffing about because you overshoot with the hand wheel or that last digit keeps changing and the ball screws and motors will hold position so no need for locking axis

4= G-code. This is the language that the CNC uses to tell it what to do, some enter a few lines manually others use a post processor combined with their CAM package to generate this code. Once the code is loaded into the CNC a suitable tool loaded and position (datum) of the work and tool set the program can be started and the tool will just work down the lines of G-code

I mostly tend to use number 4 with number 2 used for setups and the odd bit of fixture machining such as skimming the top flat and adding a couple of holes to fix the work to.