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Author Topic: loosing the z axis position during cutting???  (Read 2158 times)

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Offline Thys

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loosing the z axis position during cutting???
« on: October 03, 2011, 03:49:02 PM »
I have no other way to title this, but let me elaborate,

I use cambam to generate G code and run a program in Mach 3. My lead screw for the z axis is an m8 metric thread with a pitch of 1.25mm. my x and y axis are on a sprocket and chain system and can attain much higher speeds than the z axis. When cutting tonight and 1200mm / min, it seems that the z axis gets out of calibration / position or something as half way through the process, mach 3 shows 3mm above surface, but the spindle is virutally on the wood. ( at position zero) then later, it's even further down at -2 or -3 and mach 3 says the spindle should be at 3mm.

I am not sure but could it be when the spindle jumps over the triangular tabs which cambam makes, it is a little too fast for the metric lead screw to wind up and wind back down again?

It is really frustrating as you could imagine as I loose good wood in the process and waste.

any comments or assistance would be greatly appreciated,
Thanks
Thys
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Offline Hood

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Re: loosing the z axis position during cutting???
« Reply #1 on: October 03, 2011, 04:05:08 PM »
Sounds like you are stalling on rapids the way up and losing steps, try reducing your acceleration and velocity and see if it helps.
Hood

Offline RICH

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Re: loosing the z axis position during cutting???
« Reply #2 on: October 03, 2011, 04:50:23 PM »
Do as Hood replied. You don't say how long you have used the machine. No matter how you tune .....only after use will you find what settings will be reliable and repeatable. May not like the feedrates and rapid velocities but that's a different topic.

RICH

Offline BR549

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Re: loosing the z axis position during cutting???
« Reply #3 on: October 03, 2011, 07:18:01 PM »
The Z axis screw is MUCH to fine compared to the XY axis as far as speed and Stepper RPMs. You will stall the Z every time trying to run high feedrates.

You are going to have to calculate what the best RPM for the Steppers are and then back that into the correct feedscrew rate to get SPEED at the correct stepper RPMs. You may then run into your stepper is NOT powerfull enough to accelerate the feed fast enough once you get the speed up.
(;-). TP

Offline Thys

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Re: loosing the z axis position during cutting???
« Reply #4 on: October 04, 2011, 02:39:18 AM »
thanks so much guys, I think you have nailed it on the head. I will try and improve the setup. Thys