Machsupport Forum

Support => Forum suggestions and report forum problems. => Topic started by: thestruuus on May 31, 2008, 09:21:00 PM

Title: skip in z axis
Post by: thestruuus on May 31, 2008, 09:21:00 PM

While cutting a design I have been getting a skip in the Z axis. By skip I mean it starts out with the Z=0 at the surface of the piece. Then for some reason it thinks that z=0 is inside the piece. It's like the software commanded a step down without decrementing the DRO or that it incremented the DRO without stepping the the motor.  I have only been seeing this on the Z and it has been happening several time over the past week.  My setup is steppers not servos, not sure what other information is required.  The skip is large (>1/8" as bad as +1/4 inch)  As you can imagine this destroys the piece which is very irritating when the skip happens 1 hour into a carving.

Any ideas?

Title: Re: skip in z axis
Post by: benjamint76 on June 09, 2008, 11:58:23 AM

do you have a loose set screw or something silly like that. I have run into that problem in the past

Title: Re: skip in z axis
Post by: thestruuus on June 09, 2008, 05:39:20 PM

I was thinking that but it doesnt seem to be the case.  My plan is to tear apart the entire Z axis hardware and make sure everything is tight.

Chris

Title: Re: skip in z axis
Post by: Chaoticone on June 09, 2008, 07:36:06 PM

Chris, can you get the problem to repeat accurately? If you run the same code back to back does it mess up in the same place each time? If you can, test it and note which line of code it is on when it goes haywire. If it doesn't repeat consistently, I would guess its a mechanical problem. If it does, post your code with some notes as to where it goes haywire.

Brett

Title: Re: skip in z axis
Post by: Bodini on June 13, 2008, 04:33:41 PM

What verson of Mach are you using?  I had this problem when I switched from 2.58 to 2.63+.  If the Z motor is tuned faster than the x or y, it skips... sometimes. 

Title: Re: skip in z axis
Post by: thestruuus on June 30, 2008, 05:36:41 PM

I have concluded that this problem is not hardware related. The assembly is tight and there is no play at all in the vertical axis.  Also due to the number of steps required to cause the 1/4" movement I suspect that a random spike on the control line could not cause this.  The drop is not gradual, it just dips in 1/4"and keeps going like nothing happened.  I suspect it happens when it tries to raise the Z to jog but for some reason it fails to raise. 

I am using 2.63. The problem does not happen at the same spot every time in the Gcode. I am at a loss on this one.

I have attached the TAP and a photo of the damage.

Chris

Title: Re: skip in z axis
Post by: Chaoticone on June 30, 2008, 07:56:42 PM

Chris, If it doesn't repeat I suspect noise. Still not ruleing out others but I think that may be the problem. Can you post some pics of the controller, wireing?

Brett

Title: Re: skip in z axis
Post by: thestruuus on July 01, 2008, 06:39:18 AM

if it was noise shouldn't it be a gradual step, and sometimes it would step up sometimes down. Also I would suspsect that other axis would be affected.  I will see what I can do to clean up the wiring.

Title: Re: skip in z axis
Post by: Overloaded on July 01, 2008, 08:36:12 AM

Here is something you could check.
This is a clip from the manual.

See that the Accel. of the Z axis is not grossly different than the other axis's.
If it is, make them nearly the same and try again.

Just a possibility,
RC

Title: Re: skip in z axis
Post by: Hood on July 19, 2008, 03:49:32 AM

Have you got torch height control enabled?
Hood

Title: Re: skip in z axis
Post by: thestruuus on July 19, 2008, 07:14:02 AM

what is torch height control?

Title: Re: skip in z axis
Post by: Hood on July 19, 2008, 05:24:18 PM

Torch height control is meant for Plasma cutters but I was just wondering if there was a possibility of it being enabled by mistake.
Hood