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Z Axis problem
« on: March 11, 2007, 10:25:54 PM »
I have been having some problems with my Z axis.  I use LazyCam to import a JPEG and convert it to G-Code.  I load the code into the Mach 3 Controller.  About half way through the cutting process I notice that my cutter is no longer in the material.  It looks like the cutter has been slowly ramping in the positive Z direction.  If I look at the Z axis during the engraving process it is moving up and down the way I would expect, but it must be slowly incrementing itself in the positive (upward) direction.  However if I look at the Z axis DRO it is indicating a negative value which would seem to indicate that the cutter should be in the material.  Am I missing a setting? I am confused.  Any suggestions?

I am using the following software versions:
Mach 3: Version R2.0.024
LazyCam: 2.00.032 Standard Edition

Thanks.

Offline Chaoticone

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Re: Z Axis problem
« Reply #1 on: March 12, 2007, 07:55:40 AM »
Tell us more about your set up. Is it a mill, router, etc.? Is it skipping steps, tool pushing up in the spindle? spindle moving up? Also, post your g-code.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

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Re: Z Axis problem
« Reply #2 on: March 12, 2007, 03:28:20 PM »
I am in the process of building a 3 axis gantry type cnc router.  The motor drivers are Gecko 340 and I am using them with DC Brush type motors.  All three axes use acme leadscrews and circular rails with plain sleeve bearings; although I think I am having problems with stiction and will probably change over to ball bushings.  The spindle I am using is a Rotozip or a Porter Cable 690 Router.

I don’t think it is skipping steps because the error checker on the servo drivers don’t let me operate unless the feedback from the encoder is within some allowable error.

I checked the tool, spindle and the hardware and it all appears to be tightened down.  I measured some positions and made some tool marks to see if anything is slipping but it does not appear to be.

After giving it some more thought I think the problem might be the shaft couplings.  I am using jaw type couplings so it easy to take the motors on and off, but these type couplings have backlash in them.  Since the Z axis is moving up and down with such a high frequency I think the backlash error is adding up slowly and therefore giving me a tool offset error.  I am going to try and switch to a rigid coupling or a beam type coupling.

Any thoughts?

Thanks again.

Regards,
Bob

Offline Chaoticone

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Re: Z Axis problem
« Reply #3 on: March 12, 2007, 03:40:46 PM »
Hey Bob,
    Sounds like a good place to look. No, I don't think you are skipping steps since you are running servos. If it starts off at the right depth and gets shallower the longer you run it, I would think you defiantly have a slipping problem. Do you know how to check your steps per and make certain they are right? Can you post the code you are running?


Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!