Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: charlietuna on December 22, 2007, 05:35:43 PM
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Greeting to All,
I am having a problem locating the problem (and a fix) for my z axis. It gradually "gains" height as the job progress. It is most noticeable when doing complex carvings such as those in vcarve that require a lot of small z axis movements. By the end a job it may have "added" as much as an inch. I usually end up carving fresh air. The x and y axis seem to be working great even with a high demand of detail. I have made some successful engravings such as my name and other basics like circles, squares etc. Here is what I have and what I have done so far. Any other advice?
Equipment/Software:
Sosylva designed cnc router (the large one, all belt driven), A dedicated P4 3.2 ghz w/XP Pro, Registered Mach 3, Vcarve Pro 4.5, Xylotex 3 axis board, CNC4pc BOB. There were no "known" modifications to any design and all parameters were meticulously set according to ALL of the aforementioned documentation. This machine runs like a dream and has since day one. The 289 oz steppers run very smooth at available speeds or accel.
With all of the possibilities like missing steps, resonance, binding, noise, settings, etc......Here is what I have tried so far:
1. Lots of reading and re-reading of all manuals/instructions.
2. Lots of reading and re-reading of forums like this one.
3. Changing the active low/high setting for step and dir. (no change)
4. Tried various speeds and accelerations. My last one was 15, 1. (no change)
5. Rechecked the xylotex board for proper voltage ref - 3.35 (no change)
6. Reduce the likelyhood of noise by using shielded cable and not with any power cables. I do not have limit or home switches yet. (no change)
7. Adjusted the debounce intervals, now at 5,000. (no change)
8. Finally, I removed the belt and gears completely from the zaxis and made a reference mark on the back of the stepper and ran a "dry" run under no load. I have repeated this with x & y disabled as well as the spindle motor off. (NO CHANGE)
Any thoughts?
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Tried swapping X or Y axis drive for Z, I am not familiar with the Xylotex drives but I presume that even though its a 3 axis drive system each drive will be kind of independant.
Hood
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Thanks for the quick reply Hood,
I just tried it with the same results. I am still doing this with no load and the other two axis disabled to eliminate at least a few variables. Would changing the microstepping to 1/4 rather than 1/8 help? If so, should it be done for all axis and will it affect the resolution greatly?
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OK next thing I would do is configure the X or Y axis as the Z axis in Mach and see if the X or Y now loses position.
Hood
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Hi, Charlie
In Motor Tuning have you tried setting the Step/Dir Pulses from 0 up to 5.
It will give your stepper control more time to see the Pulses from Mach.
Thanks, Chip
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Are you sure it isnt in the g-code? I'm just askin'. :)
-Nick
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Ok..Chip first,
Thank you. Yes, I have tried step/pulses at ALL 0-5 using various vel. and acel. all with the same results.
Hood, I just switch my x for the z and the z behaves in the same incorrect manner.
Just to clarify a little, I am trying to execute a photocarve image. These movements are so tiny that they almost seem to make the motor "chatter".
Let's keep going......
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Hood, I just switch my x for the z and the z behaves in the same incorrect manner.
Not sure exactly what you did here, what I was meaning was take the Z axis in Mach and configure it to the pins you currently use for the X axis. This means when you run the code the X axis will do the Z moves. If the X (now doing Z moves) keeps position then its hardware, if it loses position then its software.
If this is what you did then apologies.
Hood
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Hey Nick,
G-code? It's certainly an option but I am still thinking no at this point. The DRO in Mach3 is consistently displaying a safe travel of 0.200 during the project.which is what was set in the photocarve program. The other axis seem to work great. Photocarve, like Vcarve, has the ability to save the tool path according to a chosen post processor - in this case Mach2/3. Although I am familiar with gcode to a point I am not sure what I would be looking for.
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Hood,
Yes, I did exactly as you described. I am almost positive is NOT a hardware issue. I just don't know where to go from here. Something just ain't right.
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OK so the X axis was out of position when it was acting as the Z axis?
So now try just writing some simple code doing G1 moves up and down and see if it ends up in the correct position.
Hood
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Hood,
Ok, I ran the following gcode loop.
F1000 (faster than needed but limited in Mach3)
G20 G90
M98 P1234 L50
M30
G1234
G1 Z.5
G1 Z0
M99
The other parameters were: 25000hz, dir/step set to active low, 30 vel. 1(one) accel., pulse 5, still under no load using a reference mark on motor and shaft.
This ran 50 times and the end result was off zero by 0.07inch. Hmmm
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can you attach your xml please
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So when you say it's 0.070 off, you mean after you run the gcode and the Z dro reads 0.000, but it actually measures 0.070 higher than you started?
Could backlash comp throw it off a little over time if improperly applied? (asking Hood or gurus)
-Nick :)
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Hey Charlie,
If you were to run the M98 L50 several times, would the error be exactly the same each time ?
If so, hmmmmmm.........If not, there may be something causing you to miss steps when Z up. Intermittently/randomly. It would take a while to accumulate. Physical bind in the axis maybe ?
Maybe try the same code at slower feed speed. See if the error is the same as when run fast.
Also, I had a similar symptom once....the dang motor shaft coupling was not tight enough and ever so gradually mine would get out of whack. Just a little at a time, but it drove me nuts till I caught it. They were clamp type helical beam couplings...have to be really tight.
Just a thought.
Good Luck,
RC
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Just a thought but do you happen to have a counter balance such as a set of springs on your Z axis that are over sized and causing it to creep?
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Man, I really appreciate all of the advice from everyone. Let me catch you up.
First, when running the trial loop the amount "off" was pretty consistent. Increasing the number of loops increases the amount "off".
GaryB, I am not using a counterbalance, if anything I would expect my z to drift downward due to the weight.
So...up and early this morning. I completely dismantled the z and checked everything, reassemble and it's smooth as a baby's bottom and very easy to move freehanded. I did change the microstepping to 1/4 and BINGO...spot on! I ran the loop a few times with perfect results. I then enabled all axis' and ran the photocarve image. Great news, it was able to maintain it's depth.
NOW for the bad. My x and y are now stuttering and loosing steps. You can hear it and obviously see it. They are just fine when jogging around. In fact, they sound great. I decided to change the x and y over to 1/4 microstepping as well but this did not help. Before, these ran very smooth. I've been doing this all morning, trying various settings. This machine is on the verge of greatness. Any thoughts now?