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Egg shaped holes
« on: June 04, 2016, 12:12:28 AM »
I'm getting egg-shaped holes when pocket milling with Mach 4. The holes are 3 mil out of round. Using Mach 3 I got only 1 mil out of round. The holes in Mach 4 are also undersized about 10 mil (average). Mach 3 always came out right on size.

Such a weird problem. Is anyone else seeing this? Could it be the backlash parameter is not being implemented correctly in Mach 4? I'm using the same backlash value on both programs.
« Last Edit: June 04, 2016, 12:16:21 AM by Grimey »

Offline dude1

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Re: Egg shaped holes
« Reply #1 on: June 04, 2016, 01:59:31 AM »
Backlash is a ********* to use try doing some test holes and each one up the acc, I found if you tune your acc thing work better
Re: Egg shaped holes
« Reply #2 on: June 04, 2016, 09:41:21 AM »
I can say that all parameters (accel, etc) are the same between Mach 3 and Mach 4. It worked well in Mach 3...why doesn't it work well in Mach 4
« Last Edit: June 04, 2016, 09:43:26 AM by Grimey »

Offline dude1

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Re: Egg shaped holes
« Reply #3 on: June 04, 2016, 07:00:10 PM »
because the program is faster but use the same trajectory planner as M3, I had the acc a lot higher in M4 than M3, tuning the acc was the only way I could get it to cut well in 3D cuts 0.001 mm over a 1000 moves. if I did not tune it it was all over the show with 3D cuts, 2D where fine but are even better, it's doing the 2.5D, 3D where you can have problems.
Re: Egg shaped holes
« Reply #4 on: June 04, 2016, 09:30:18 PM »
ok, I'll try. I have an open loop machine. I suppose if accl is too high, it will just lock up.

Is there a rule of thumb in setting the accl?

Offline dude1

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Re: Egg shaped holes
« Reply #5 on: June 05, 2016, 01:26:30 AM »
mines open loop to accl what works well, how I do it is I turn all but one axis off run the code to it's good then do the other axis just one at a time for me X and Y are quite quick to do Z can take hours but Z has a problem that is going to cost some money to fix. this works for me on one off the machines I have, on the other one It does not need done one is chines crap the good one is German   

Offline Chaoticone

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Re: Egg shaped holes
« Reply #6 on: June 05, 2016, 12:18:17 PM »
Mach4 does not do any backlash compensation. If using Mach4 the backlash compensation is handled by the motion device. If your motion device does not support backlash compensation then you do not have backlash compensation. The backlash units entry in motor tuning is a convenient place for motion device plugins to get that information from, nothing more.
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Offline Pedio

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Re: Egg shaped holes
« Reply #7 on: June 05, 2016, 12:52:02 PM »
The first thing to do is grab the head (spindle) of the machine while the machine is on and not moving. Move it back and forth and see if there is any play. If the spindle moves a little before you can feel resistance. Be careful and don't break anything (in case you have a very small mill) If there is you need to tighten up the motor placement, chains, etc. This is pretty easy to do on most machines. Then do a real measurement of backlash and see what you have left. This is where the fun begins!
Re: Egg shaped holes
« Reply #8 on: June 05, 2016, 01:45:46 PM »
I'm using smooth stepper. Clearly it was using the backlash compensation in Mach 3. Anyone know if the versions for Mach 4 are using htis?

The other issue is the undersized holes, about 10 mil too small. There's obviously something else going on!

And no, it's not spindle play. As I said, the holes were fine in Mach 3. Something has changed...

Offline Pedio

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Re: Egg shaped holes
« Reply #9 on: June 05, 2016, 02:02:22 PM »
It sounds like your units are out of wack. Try making a box as large as possible and cut it out with a straight bit that you know the exact size. Cut on the inside of the line. Measure the sides of the box to see if it is correct. You can then calculate how far off your units are. Of course it is better to calculate what your units should be from gear teeth, steps, etc. instead of calculating from how far out the actual cut is. At least you will know which is axis is off and approximately what the steps per unit should be.

You can use (Steps programmed into M4)*(programmed move distance)/(actual move distance)=(Estimated steps to try in M4)

Repeat to confirm.