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### Author Topic: Problem with pocket holes and z axis  (Read 4586 times)

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#### ajl53

• 15
##### Problem with pocket holes and z axis
« on: January 11, 2013, 06:32:44 PM »
Hello,
I'm making new uprights for my diy cnc machine. I drilled the original one on a drill press.....
It seems that each time it goes to pocket a new hole, the z axis moves up off of the zero point.
X and Y move to the correct spot, but each successive hole is shallower than its predecessor.
I'm using .5 inch aluminum and the depth of the pocket is .55 inches. I've attached the g-code that CamBam produced.
Any help would be greatly appreciated as I can't figure this one out!!!!
Thank you
Art

#### woodspinner

• 100
##### Re: Problem with pocket holes and z axis
« Reply #1 on: January 11, 2013, 06:54:02 PM »

John

#### Hood

• 25,835
• Carnoustie, Scotland
##### Re: Problem with pocket holes and z axis
« Reply #2 on: January 11, 2013, 07:50:58 PM »
Could you be losing steps with the rapid move up in Z axis? Try decreasing your acceleration by half and see if it helps.
Hood

#### ajl53

• 15
##### Re: Problem with pocket holes and z axis
« Reply #3 on: January 11, 2013, 08:24:43 PM »
Actually that made it worse. As it went to the second hole, the z axis was at least 1/8 inch too high!!
Any suggestions?

#### Hood

• 25,835
• Carnoustie, Scotland
##### Re: Problem with pocket holes and z axis
« Reply #4 on: January 12, 2013, 03:48:24 AM »
Lowering acceleration should never make it worse, attach your xml and I will test here.
Also does the DRO show the correct position and its just the cutter that is wrong or does the DRO show the wrong position?
Hood

#### ajl53

• 15
##### Re: Problem with pocket holes and z axis
« Reply #5 on: January 12, 2013, 08:33:55 AM »
Hi,
The Mach display is showing the correct numbers and the x and y axis are correct physically, but the z axis is always physically HIGHER than it should be.
Am I correct in assuming that if it was missing steps in should be lower?
Thanks

The g-code is attached to the first post.

#### woodspinner

• 100
##### Re: Problem with pocket holes and z axis
« Reply #6 on: January 12, 2013, 08:46:23 AM »
did the first hole go all the way thru?

John

#### Hood

• 25,835
• Carnoustie, Scotland
##### Re: Problem with pocket holes and z axis
« Reply #7 on: January 12, 2013, 08:57:51 AM »
The Mach display is showing the correct numbers
That suggests Mach is doing things correctly as the output from the driver is monitored and that is what sets the DROs.

Am I correct in assuming that if it was missing steps in should be lower?
Thanks

If its losing steps on the way up that would be the case but it could be losing steps on the way down. The other thing would be to check that you have the active state of the Z Step pin set correct for your drives, this however shouldnt really be the problem in this code as it would show up more in code with lots of Z Direction changes.

The g-code is attached to the first post.

I also need your xml so I can check your code running the same settings as you.

#### ajl53

• 15
##### Re: Problem with pocket holes and z axis
« Reply #8 on: January 12, 2013, 09:00:58 AM »
Yes, the first hole seems to be correct....

Hood... if you meant the backup xml from Mach... Its attached

#### Hood

• 25,835
• Carnoustie, Scotland
##### Re: Problem with pocket holes and z axis
« Reply #9 on: January 12, 2013, 09:15:44 AM »
XML seems fine and seems to run ok here but cant see any mention in it of device selected for some reason. Are you using the parallel Port?
You have the kernel at 35KHz but for your motor tuning that is not needed so suggest you set to 25KHz and restart Mach.
You could also try using Sherline mode to widen the pulse.
Hood