Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: bbristow on July 08, 2010, 04:16:05 AM
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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
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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.
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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
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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.
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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.
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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.
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.
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Yes, just moving the head up and down as little as 10-20 times I can see that I am off.
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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.
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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?
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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
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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
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Maybe a daft question but it's not backlash?
Brian
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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
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I found my problem and solution. It was interference from the computer. I replaced the PC and all problems are gone.
Frank
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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
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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.
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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....
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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.
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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.
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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.
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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
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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
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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
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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
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JR,
Do you get lost steps on any other axis or is it just the Z ?
Tweakie.
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Just the z.
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Hi,
While I see this post has been dormant I am hoping you can steer me in the correct direction. I am seeing occasionally a loss of Z, in the .060" range.
I Zero the machine, move the spindle to 2.00" above, check with a 1x2x3 block (on the 2" edge) and looks fine. Run a couple of paths ( generated with Fusion 360) and I see roughly .060" clearance between the 1x2x3 block after moving the spindle to 2.0". The Collet is tight using torque wrench set at 50lbs (1/4" bit).
Remember the DRO is showing 2.0" so if I rezero the z-axis the DRO should never see anything above 2.0". Correct? That is not the case I see a value of 2.057" ish just as I hit the zero operation. See pictures below.
Its an AVIDCNC like, lot of the part are from AVID, the exception is the controller. I am using a ESS from the Boardroom, ClearPath Nema34 servo's and various PS. If I was suffering from noise I would expect to see it on all axis. I don't I only see this in the Z-axis. Spindle rack is AVID and the Spindle is also from AVID. The Rack-Pinion is from AVID also.
Thanks
Loren
PS. I have simulated this and haven't seen it 'fail' using both NCViewer and the fusion built in version. the code is very simple, just taking .01." off the side wall using a 2D contour.
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Hi,
While I see this post has been dormant I am hoping you can steer me in the correct direction. I am seeing occasionally a loss of Z, in the .060" range.
I Zero the machine, move the spindle to 2.00" above, check with a 1x2x3 block (on the 2" edge) and looks fine. Run a couple of paths ( generated with Fusion 360) and I see roughly .060" clearance between the 1x2x3 block after moving the spindle to 2.0". The Collet is tight using torque wrench set at 50lbs (1/4" bit).
Remember the DRO is showing 2.0" so if I rezero the z-axis the DRO should never see anything above 2.0". Correct? That is not the case I see a value of 2.057" ish just as I hit the zero operation. See pictures below.
Its an AVIDCNC like, lot of the part are from AVID, the exception is the controller. I am using a ESS from the Boardroom, ClearPath Nema34 servo's and various PS. If I was suffering from noise I would expect to see it on all axis. I don't, I only see this in the Z-axis. Spindle rack is AVID and the Spindle is also from AVID. The Rack-Pinion is from AVID also.
Thanks
Loren
PS. I have simulated this and haven't seen it 'fail' using both NCViewer and the fusion built in version. the code is very simple, just taking .010 . off the side wall using a 2D contour. The main cut is a Pocket at .020in over and the Final Cut is Contour taking -.010in. Both paths has the Axial at 0.