Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: bbristow on July 08, 2010, 04:16:05 AM

Title: Z Axis Drifting or Loosing Steps?
Post by: bbristow on July 08, 2010, 04:16:05 AM
Please HELP!  I am pulling my hair out…
I have been having this problem now for a while, but have been able to avoid it until now.  It seems that my Z-Axis is drifting or loosing steps.  What makes it more difficult to figure out is that it seems to be a math error of some kind as the results I can duplicate accurately. 

I am thinking this is a Mach 3 issue since I can duplicate the results.

Here is an example….  I am cutting a 3d part, I can let it cut the file out and when it is finished, it thinks the z axis is at 0.0, when it is actually at 0.25.  I can cut the part again after re-zeroing it and I end up at pretty much the same offset.  I am doing parallel finishing; I can see the bit is gradually and smoothly cutting lower and lower.  There is no big jump; it just seems to smoothly drift.
I can also zero the machine and toggle the head up and down about 15-20 times and will check zero and it will be off again.  I can do this at any speed setting and I let it completely stop before changing direction and I still produce the same results. 
This is what I have tried so far with no change….
Tried changing frequencies to 3 or 4 different settings.
Tried the shirline ½ step mode.
Tried setting the pulses under motor tuning to 5, then to 15, then to 20.
Tried changing the number of pulses per inch from 3200 (Setting I was running at) to 2000, to 1600, to 1000 and I still see the same results.

I am running the Joes 4x4 hybrid machine.  You can see it here
http://www.saberfire.com/gallery/Projects/CNCMachine/

I am Running Mach 3 with the Hobby CNC Pro kit with the 305/oz motors.  I have the jumpers set to quarter step.
I am not sure what else to do here?

Thanks,
Bobby
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Tweakie.CNC on July 08, 2010, 04:59:15 AM
Bobby,

Sounds to me like a classic case of lost steps.
A common cause, when this happens with the Z axis only, is binding or tight spots in the screw or slides. Try halving the velocity and acceleration, in motor tuning, and see if it still happens (the effect of this will be to increase stepper motor torque). If this cures it then experiment to achieve the best reliable settings.

Tweakie.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Hood on July 08, 2010, 05:20:18 AM
I wonder at this bit
Tried changing the number of pulses per inch from 3200 (Setting I was running at) to 2000, to 1600, to 1000 and I still see the same results.
I cant see how you can get the same results (0.25 higher) with different steps per unit unless the cutter is being pushed into the collet by that amount.
Try running the file without material and see if its still high at the end.
Hood
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: bbristow on July 08, 2010, 01:26:12 PM
Bobby,

Sounds to me like a classic case of lost steps.
A common cause, when this happens with the Z axis only, is binding or tight spots in the screw or slides. Try halving the velocity and acceleration, in motor tuning, and see if it still happens (the effect of this will be to increase stepper motor torque). If this cures it then experiment to achieve the best reliable settings.

Tweakie.

I have tied slowing the speed down to to a painfully slow 20 inches per minute and let the machine stop before changing directions, and I still see the issue.  What bothers me is that this seems to be a math error.  It happens all the time and happens consistently.  I.E.  I can cut the same part over and over again and each part will be identical with the axis slowly drifting on every single one by the same amount.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: bbristow on July 08, 2010, 01:30:00 PM
I wonder at this bit
Tried changing the number of pulses per inch from 3200 (Setting I was running at) to 2000, to 1600, to 1000 and I still see the same results.
I cant see how you can get the same results (0.25 higher) with different steps per unit unless the cutter is being pushed into the collet by that amount.
Try running the file without material and see if its still high at the end.
Hood

Sorry, let my clarify.....  It is not off by the same amount when I change steps, it is just off no matter what the setting is, but always slips further down.  I.E...So when it thinks it is at 0.75 the bit is really at .72.  I can move the head up and down without cutting anything about 10 times and see that it is off.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Tweakie.CNC on July 08, 2010, 01:39:17 PM
Quote
What bothers me is that this seems to be a math error.

This is unlikely - there are so many users for so long, if this was the case it would have been discovered and corrected a long long while ago.

Quote
I can move the head up and down without cutting anything about 10 times and see that it is off.

Are you saying that just jogging the Z axis up and down produces this error ?.

Tweakie.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: bbristow on July 08, 2010, 01:41:58 PM
Yes, just moving the head up and down as little as 10-20 times I can see that I am off.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Tweakie.CNC on July 08, 2010, 01:50:58 PM
I think I am back to what I thought earlier - lost steps.

Tightness, binding, excess speed and electrical noise are all possible causes but electrical noise usually affects more than just one axis.
If you are absolutely sure it is not binding or excess friction on the axis then I would suspect the motor or possibly a loose coupling on the screw.

Tweakie.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: bbristow on July 08, 2010, 02:31:40 PM
I think I am back to what I thought earlier - lost steps.

Tightness, binding, excess speed and electrical noise are all possible causes but electrical noise usually affects more than just one axis.
If you are absolutely sure it is not binding or excess friction on the axis then I would suspect the motor or possibly a loose coupling on the screw.

Tweakie.

I have the power for the motors and controller going through a power conditioner as a friend of mine had a problem with noise, but that showed up as random z spikes in the cut files. 

If I am loosing steps, what would cause the Z to loose steps so precisely?
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Hood on July 08, 2010, 03:29:55 PM
As Tweakie says it is almost certainlylost steps, could be binding, noise or even a bad drive or motor. Cant see it being a setup issue but if you want to attach your xml I will have a look through it.

As for your Z test, if you move up and down 20 times at rapid, then same at half speed and same at a crawl is it always the same amount out?
If you then move a longer distance doing the same 20 moves is it the same amount out?
Hood
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: alenz on July 09, 2010, 02:39:42 AM
I seem to remember a similar situation some time ago where the fix was to reverse the step low/high in config/ports and  pins. (Then toggle the reverse setting in config/homing/limits to keep movement in the proper direction). It's a long shot, but will only take a minute to check out.
Al
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: bwprice100 on July 09, 2010, 04:57:44 AM
.
Maybe a daft question but it's not backlash?

Brian
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Frank Boon on July 25, 2010, 03:58:50 PM
Hi Bobby, you are not alone in this.

Since yesterday I have the same kind of problem. The Z is moving down twice the distance that it moved up. So when I zero Z and jog up till 70, and than jog down again the Zero point is at +35.  So after each Z move up, it diggs in half of the lift.
Spindels and all are clean and move without friction. I tried pushing up and pulling down the Z during movement, always same results. Stepper makes the same sound in both directions.
Replaced the microstep driver.
 ???
I will post here again if I find something.
Frank
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Frank Boon on July 30, 2010, 06:04:41 PM
I found my problem and solution. It was interference from the computer. I replaced the PC and all problems are gone.
Frank
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: willliiee on September 09, 2010, 01:42:55 PM
my first thought is with the z, as i am finding out, correct counterbalancing is pretty important...   have you experimented with different weights or even have it counterbalanced???   bill
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: xaco on September 15, 2010, 04:21:55 PM
hi,i had similar problem with y-axis,after i finished job  ,the tool was  always few milimeters off the zero,my problem was the rubber conection  that was holding screw and motor together.i realized that after someone suggested me to run my y axis at extra slow speed,and there it was,motor was running but  tool didnt.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: ALL Signs on February 03, 2011, 09:13:12 PM
Hi
I am having the same problem, have you found a solution ?
This is how It occurs on my machine....
I have purchased aspire 3 upgrade, last week. I have run preliminary tests: The z-axis is diving down while cutting, it progresivly lowers its posision while cutting a 3d image, not by much but it is steadily working its way down into the table. I have found a thread about this on the aspire forum but there was no resolution to this problem, I have taken all the steps sujested but I am still having the same problem with the z axis.

I am pograming on a computer running vista, 6gb ram - then exporting to a computer running xp via a memory stick, into Mach3, this computer runs my cnc router, I have sucsesfully used V-carv pro on this machine before Aspire with no such problems.

Please advise....
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Tweakie.CNC on February 04, 2011, 02:06:17 AM
From what I have read on other forums this appears to be an Aspire problem (within the GCode generated).
If your Z axis DRO shows the increase in depth then there is a more than good chance it is in the GCode and not your machine.

Tweakie.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: jr_82 on April 15, 2011, 10:42:53 PM
My Z does the same thing, But it is always high by about .25 in at the end of the program.  It is a constant.  I have tried different parallel ports and different motors.  Nothing seams to work. My Y axis used to do the same thing only on a much larger scale. It would be off by inches after a few moves.  Then it stopped and is correct again. But the Z axis is now doing it.  I have even switched the x and y outputs but the result is that the x axis would now be off.  I have tried several different breakout boards with the same result.  I am at a loss.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: ger21 on April 16, 2011, 07:24:11 AM
My Z does the same thing, But it is always high by about .25 in at the end of the program.  It is a constant.  I have tried different parallel ports and different motors.  Nothing seams to work. My Y axis used to do the same thing only on a much larger scale. It would be off by inches after a few moves.  Then it stopped and is correct again. But the Z axis is now doing it.  I have even switched the x and y outputs but the result is that the x axis would now be off.  I have tried several different breakout boards with the same result.  I am at a loss.
Lower your Z axis acceleration by half. It's losing steps on the complex 3D moves.

I had exactly the same problem. I had been using my machine to do 2.5D cutting for months with no problems, but when I started cutting 3D parts, I had the same problem. Slow down the Z accel and the problem went away.

Title: Re: Z Axis Drifting or Loosing Steps?
Post by: RICH on April 16, 2011, 03:28:39 PM
In my case, just like Gerry's reply, I was missing steps and pulled my hair out trying to find the culprit. Machine 2.5D all day,but would randomly skip steps on 3D stuff and you coud not hear when or where it happened. Playing with settings didn't do any good.
So I replaced the steppers with ones of  two and half times  the original torque rating, got rid of the backlash in X and Y axis by replacing  the bearings and adjusting the ball screw nuts, and life is good again. Now if i would only get off my lazy butt and redo the Z axis life would be really good on the mill.
RICH
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: jr_82 on April 16, 2011, 04:02:43 PM
I  have slowed the z axis way down and reversed the settings as someone else suggested.  It is much more accurate now.  I am making a gun stock.   Lots and lots of Z movement. It always worked O.K.  if I finished using the long axis X,  but when I finished using the Y axis going the short distance back and fourth across the material there is a lot more z movement

Thanks
JR

Title: [possible solution] Re: Z Axis Drifting or Loosing Steps?
Post by: mbele on April 21, 2011, 11:25:58 AM
Hi,

I had a similar situation - Z axis would "drift away" after many moves.
Eg. after test case with 500 runs of subroutine that moves 10mm up+down, zero position would consistently be arround 4 mm to low. That makes arround 0.004 error per move (less than one microstep in my setup which is 0.0125mm).
Anyway, after I tried/checked all that was suggested in this thread, finaly changing the kernel speed from 35kHz to 25kHz made it work perfectly.
HTH
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: jr_82 on April 21, 2011, 01:11:52 PM
I am already at the 25kHz It is close but still after 25,000+ lines it is about .1in off not bad on wood I can fix most of that with sandpaper.

Thanks
JR

Title: Re: Z Axis Drifting or Loosing Steps?
Post by: Tweakie.CNC on April 22, 2011, 01:55:43 AM
JR,

Do you get lost steps on any other axis or is it just the Z ?

Tweakie.
Title: Re: Z Axis Drifting or Loosing Steps?
Post by: jr_82 on April 22, 2011, 09:21:44 AM
Just the z.