To the dark side CNC

[Stuart]

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

[Jo]

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

[Stuart]

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

[Vixen]

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

[jadge]

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

[kvom]

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.

[jadge]

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:



Andrew

[Dave Otto]

Your parts look real nice Andrew; what type of machine do you have?

Dave

[Hugh Currin]

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

[Tennessee Whiskey]

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

[MMan]

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

[Vixen]

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

 

[Vixen]

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.



How close are you to Fareham Hampshire?

Regards

Mike

[MMan]

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.

[Hugh Currin]

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