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Author Topic: Need serious help with z-axis...  (Read 3660 times)

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Offline Chet

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Need serious help with z-axis...
« on: May 03, 2012, 11:49:54 AM »
I've asked this group for help on this issue before and have implemented the many suggestions. Thank you!
However I'm still getting the random loss of Z-axis positioning. (Typically plunging deeper into the cut than specified.)
Typically this will occur anywhere from a 1/2 hour to 2 hours into the cut. (I typically do 5 hour cuts...)
It never appears to happen with the rough cut, only the finish operations.
Because it is ONLY the Z-axis, I am unsure what to do next...
These trial & error cuts are making me crazy...!!!!!
I've just reloaded the Mach3 program I use, so that should be OK.
The HobbyCNC driver seems to be OK...
I've just replaced the Z-Axis motor from HobbyCNC with its identical match...
The actual machine code appears to be fine...
The previous project cut just fine.
Any really good thoughts on a possible remedy?
I'd toyed with electrical interference on the mains, but then why only intermittently on the Z-axis?
How would you troubleshoot this situation?
Many Thanks!
Chet
Re: Need serious help with z-axis...
« Reply #1 on: May 03, 2012, 03:32:40 PM »
Chet

You say the previous project ran OK, try dry running the previous project again to see if the problem persists.

Graham

Offline Chet

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Re: Need serious help with z-axis...
« Reply #2 on: May 03, 2012, 06:06:00 PM »
That's a very interesting troubleshooting technique!
However the previous project that did run OK, only ran OK after one failed attempt...
So right now the previous project is 50/50 and would not lead to a conclusive answer.
After this most recent failure, I replaced the Z-axis motor.
But once again a failure occurred...

Offline ger21

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Re: Need serious help with z-axis...
« Reply #3 on: May 03, 2012, 06:37:10 PM »
1) Lubricate the Z axis leadscrew

2) Reduce the Z axis acceleration by 50%.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline BR549

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Re: Need serious help with z-axis...
« Reply #4 on: May 04, 2012, 01:01:10 PM »
WHat type  screws and pitch are you using for the Z?  In most apps it is critical to get the screw pitch correct for the stepper torque range. Too fine and you cannot get speed without stalling AND you cannot get high speed. In 3d work you need the Z to be the  quickest of all the axis

Just a thought, (;-) TP

Offline Chet

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Re: Need serious help with z-axis... folo
« Reply #5 on: May 06, 2012, 10:54:26 AM »
Well, I've successfully completed one of my patterns. I wanted to let you all know what changes I implemented:
1) I moved the vac and router AC supply cables from anywhere near the Z-axis motor cable.
2) I went back to my standard 3 flute carbide cutter (rather than the 4 flute cobalt I'd been experimenting with)
3) I lowered the speed of the cutter from full out, to 22,500 rpm at 20 ipm.
4) I periodically monitored the progress of the cut.
One successful cut does not mean I have solved the intermittent problem, but there is progress!
If I get 3 in a row, I'll post once again just to let you guys know at least one of the above changes was effective.
And a big thank you to all who offered their insights!!!
Chet

Offline ger21

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Re: Need serious help with z-axis...
« Reply #6 on: May 06, 2012, 12:25:43 PM »
What are you cutting? That feedrate is extremely low for that rpm.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline Chet

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Re: Need serious help with z-axis...
« Reply #7 on: May 06, 2012, 01:13:53 PM »
Styrofoam...

Offline ger21

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Re: Need serious help with z-axis...
« Reply #8 on: May 06, 2012, 01:50:11 PM »
Try 15,000 rpm and 200ipm.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline Chet

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Re: Need serious help with z-axis...
« Reply #9 on: May 06, 2012, 04:06:03 PM »
Hi Jerry!
Thanks for your suggestion.
I'll run a test piece using your recommendations...
I'll let you know how it works out.