Machsupport Forum

Mach Discussion => Mach4 General Discussion => Topic started by: Grimey on June 04, 2016, 12:12:28 AM

Title: Egg shaped holes
Post by: Grimey 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.
Title: Re: Egg shaped holes
Post by: dude1 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
Title: Re: Egg shaped holes
Post by: Grimey 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
Title: Re: Egg shaped holes
Post by: dude1 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.
Title: Re: Egg shaped holes
Post by: Grimey 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?
Title: Re: Egg shaped holes
Post by: dude1 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   
Title: Re: Egg shaped holes
Post by: Chaoticone 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.
Title: Re: Egg shaped holes
Post by: Pedio 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!
Title: Re: Egg shaped holes
Post by: Grimey 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...
Title: Re: Egg shaped holes
Post by: Pedio 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.
Title: Re: Egg shaped holes
Post by: Grimey on June 05, 2016, 03:48:39 PM
No, the units are fine.
Title: Re: Egg shaped holes
Post by: Grimey on June 05, 2016, 06:08:14 PM
Personally, I don't see how the accl parameter will change anything.
Title: Re: Egg shaped holes
Post by: dude1 on June 05, 2016, 06:37:09 PM
start and stop speed if that is bang on you don't lose steps if it out on one axis you can lose steps on a axis.

say x and y get to a spot in space and Z has not got there yet (potion 1) x and y can go to the next spot in time and Z catches up (potion 2) Z should not have it would of mist steps in potion 1 to get to potion 2, if all axis's get to a spot at the same time there will not be lost steps.

by have the acc at a rate that it get's a axis to stop and start in a smooth fast way. if you move Z to 100 and it is at 100 fine then go back to 0 then it's at 0 it looks all good, if you do the same move 1000 times it may not be back at zero because it may have been out by 0.0001 and what you measure with only shows 0.000, after 1000 moves it may sow 0.01 + or - then 10000 moves it will be at 1.
what you wont is at 1000 moves to be looking the same as 1 move. it's how I do it and it works on one machine.
if it is + or - 0.001 at one move you wont + or - 0.001 at 1000 moves
Title: Re: Egg shaped holes
Post by: Grimey on June 05, 2016, 07:07:20 PM
Accl parameter is definitely not the issue either. Since my pocket milling isn't working, I use a boring head to finish the hole. The finished hole is precisely where it's supposed to be. If steps were missed, then the hole location would be wrong.

I believe backlash is also working correctly too. If it wasn't working correctly then, again, hole location would be incorrect.

There's some other issue. And, no, it's not a worn out or mechanically loose machine!

Title: Re: Egg shaped holes
Post by: dude1 on June 05, 2016, 07:20:53 PM
nosie can do it it as well, it took me 4 years to track down every problem with my big machine, nosie was the worst problem, and it was the dust extractor pipe being to close to the power plug. and the power wires to close to the signal wires. it would make the machine do all sorts of strange things.

so just run a test on each axis say a lot of moves on one axis at a time if they are on point move on to the next axis that will take the motors and motor wires out of the posabile problem list, doing one thing at a time makes it faster
Title: Re: Egg shaped holes
Post by: Grimey on June 05, 2016, 08:01:58 PM
I appreciate everyone's help, but please read my posts. It works fine with Mach 3. Mach 4 i get weird results.
Title: Re: Egg shaped holes
Post by: dude1 on June 05, 2016, 08:17:36 PM
yer but something is a problem in M4 you need to test everything other wise you may never find the problem, what ever is wrong may only show up in M4, sort of testing everything how are you going to find it.

mach 4 is faster than Mach3 i had to up the look ahead and the acc for it to work as good as Mach3 did I tested everything to find these two things, it did not take long to find as I went through everything
Title: Re: Egg shaped holes
Post by: CCWood on June 08, 2016, 10:08:06 PM
Had a simular problems once... recalibrated, calculated & compensated for backlash... still out of round. Problem turned out to be a blown fuse going to the gecko drive on my A motor (X axis slave). X was driving, A wasn't. Replaced the fuse and all was well.