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Missing identical steps on each axis
« on: March 04, 2009, 12:31:17 AM »
Hello,

I'm a newbie here and have just completed my X2 mill cnc build. I've tried to test and set everything, but I'm still losing a few steps each roundtrip as I move each axis back and forth.  What confuses me is its nearly identical on whatever axis I'm testing.

I must be missing something, but I'm not sure where to look? 

I running Mach 3 with a Mechatronics/Easy-CNC Driver board and Xylotex 425oz motors on all axis.

Any help will be greatly appreciated.  I've been going thru all the Acc/Vel settings and nothing seems to make a difference.

Thanks,

Troy

Offline Hood

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Re: Missing identical steps on each axis
« Reply #1 on: March 04, 2009, 02:18:46 AM »
explain if you can what exactly is happening please.
Hood

Offline jimpinder

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Re: Missing identical steps on each axis
« Reply #2 on: March 04, 2009, 04:46:37 AM »
As Hood says, a little more precise information would help - but it depends on what stage you are at in your build.

Missing steps could be exactly that - the computer is putting out pulses which your motor/drive cards are missing.

If on the other hand you are running out say 25mm and then running back 25mm and finding the axis short of the start - then that could be backlash
Not me driving the engine - I'm better looking.
Re: Missing identical steps on each axis
« Reply #3 on: March 04, 2009, 07:38:41 AM »
Thanks for the quick feedback, here's what's happening:

I've set up a dial indicator on any given axis...let's say X.  I'll zero out the Mach3 DRO.  I'll move any distance on X, for example .1 inch or 1 inch, it really doesn't matter, and then move back to 0.  I'll reset the dial indicator to 0 to remove backlash error.  I'll repeat the move, 1 inch (same direction as before) and then back to 0. When I return to 0 the dial indicator has changed by .001 (that is if I'm using 1/2 steps, its proportionally less if I'm using 1/4 or 1/8 stepping).  If I repeat the roundtrip move, I'll be off by .002" and each round trip the offset continues to add up.  And this happens on each axis, exactly the same.
Of course when I move away from the 0 axis to the midpoint (.1" or 1" away), the backlash comes into play and the indicator doesn't match the exact given distance, I understand that. But when I come back to 0, I'm always off.  Each round trip loses another .001".

This is confusing to me because I've tried nearly everything.  I don't believe its a mechanical issue, everything seems to move smoothly, but I could be wrong.  It just seems like the system is dropping a couple steps each time it makes a move.

Please let me know if I'm missing any information in my description, I want to be clear and I certainly appreciate the help.

Troy
Re: Missing identical steps on each axis
« Reply #4 on: March 04, 2009, 08:01:39 AM »
Hello Troy,
  I had a similar problem.
I ran this code and saw what you are seeing.

X1 F10
X0
M47

I set the Pulse Width in motor tuning to 4 or 5...not sure which, and it was then correct.
RC

EDIT: You might also try Sherline Mode....If you haven't yet.
Re: Missing identical steps on each axis
« Reply #5 on: March 04, 2009, 08:51:43 PM »
OK, I've done another round of testing and neither changing the Pulse Width or the Sherline Mode seemed to make a difference.

I did change the Acceleration Rate really low (at or below 1) at one point and began to notice the dial indicator moving .0005 in the wrong direction before it moved the opposite direction during the axis move. It does the every time and seems like it would account for the error if it does this on every move.

Could it be that the driver board is causing some sort of rounding error on direction changes?

Any other advice?

Thanks,

Troy
Re: Missing identical steps on each axis
« Reply #6 on: March 04, 2009, 11:36:44 PM »
An upgrade to the latest version of software apparently fixed the problem.

Thanks for the leads.

Troy