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Author Topic: help with z axis creeping  (Read 7482 times)

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Offline Hood

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Re: help with z axis creeping
« Reply #10 on: December 22, 2007, 06:58:44 PM »
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
Re: help with z axis creeping
« Reply #11 on: December 22, 2007, 08:42:29 PM »
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

Offline Hood

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Re: help with z axis creeping
« Reply #12 on: December 23, 2007, 05:21:31 AM »
can you attach your xml please

Offline Bodini

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Re: help with z axis creeping
« Reply #13 on: December 23, 2007, 12:28:04 PM »
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 :)
Re: help with z axis creeping
« Reply #14 on: December 23, 2007, 12:57:32 PM »
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

Offline GaryB

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Re: help with z axis creeping
« Reply #15 on: December 23, 2007, 01:04:05 PM »
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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Re: help with z axis creeping
« Reply #16 on: December 23, 2007, 01:31:53 PM »
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?