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Author Topic: Z axis control PROBLEMS under THC control  (Read 2363 times)

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Offline BR549

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Z axis control PROBLEMS under THC control
« on: April 18, 2011, 07:46:43 PM »
Has anyone had any problems with Z axis loosing steps under THC control???.  Here the Z wants to run in exess of the  ACCL and Vel settings in the moter setup parameters. It makes the stepper skip, studder and squaw and loose steps.

The THC setting is at 20% now and still loosing steps, it used to run fine at 50%.

I have run the machine with THC off and no lost steps. I have testd the machine with advanced 3d Gcode and no lost steps after hours of running.

Anyone else notice this ??

(;-) TP
Re: Z axis control PROBLEMS under THC control
« Reply #1 on: April 18, 2011, 09:14:44 PM »
I've seen missed steps with the THC set at higher than 40%, but it does that because THC Up/Down commands are at full speed...or a percentage of full speed...with no acceleration added.  I typically run it at 10-20%.  I bump it to 20 if the surface is highly irregular.  Everything seems to work best at between 10 and 15.

Offline stirling

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Re: Z axis control PROBLEMS under THC control
« Reply #2 on: April 19, 2011, 04:15:06 AM »
Hi Terry

From what you've said, Z works fine with an accel curve i.e. with THC OFF, doesn't work fine without an accel curve, i.e. with THC ON. Also, used to work at 50% of max vel, but now doesn't work with 20%. Assuming you havn't changed max vel then...

Sh1t in the Z. (that's a diagnosis BTW - not an instruction  ;D)

Cheers

Ian

Offline BR549

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Re: Z axis control PROBLEMS under THC control
« Reply #3 on: April 19, 2011, 07:02:22 PM »
I have had the z apart to clean and check it is smooth as glass. I can spin it up and down with my fingers.

Accel still the same vel still the same.    I can cut about 2 minutes before the Z has dropped all the way to the surface .500" drop. It is loosing step on the up cycles. You can hear the motor it sounds nasty when under thc control (;-).

I think I will try the old reload Mach trick and see IF that cures it.  Only thing is it is a real PAIN to reload all the CandCNC stuff.

(;-) TP
« Last Edit: April 19, 2011, 07:04:13 PM by BR549 »

Offline BR549

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Re: Z axis control PROBLEMS under THC control
« Reply #4 on: April 20, 2011, 07:48:19 PM »
Ian after much testing I think I have had the problem all along. But most of the time I did lots of small moves that had a lot of retouch to set the top of material. Lately they cut s have been long runs on thick plate and each section can run 3-5 minutes.This gives the Z time to loose enough steps that the head drags the surface when the cut ends and the head pulls back to safe height. 

(;-) TP
Re: Z axis control PROBLEMS under THC control
« Reply #5 on: April 21, 2011, 12:06:17 AM »
Maybe a bad motor?  That's happened before.  It drove me nuts because the motor showed no signs of being bad.  It was the last thing I changed and it fixed the problem.  It's definitely not normal.  I did a job today that ran for 22 minutes.  An intricate design in 1/4" plate.