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Y-axis slipping in only one dirrection

Posted by TheJones 
Y-axis slipping in only one dirrection
August 17, 2015 02:26AM
My printer has developed an issue where the Y-axis keeps missing steps at random, but ALWAYS in the same direction. Here are some facts about my situation:

-I've got an i3 inspired build, running a standard RAMPS1.4 setup, with nema-17's.
-It ran for weeks withough problems, until this issue popped up.
-The bearings (LM10UU's) are not binding, rods are aligned, and the bed scoots freely when I pop the belt off.
-After a great deal of fiddling with the A4988's, I put in DRV8825's. They seems well adjusted and happy (with the exception of these uni-directional jumps).
-I've lowered my exceleration to 800 on X and Y (though, speed doesn't seem to make much of a difference).
-Belts are tight enough that I can't force them to skip teeth on the motor pully, but still have enough slack to be pinched together and touch each other.
-The motors are not getting hot, but I put heatsinks on them anyways, just in case.
-I have checked, and changed out my wiring for that axis (thought it might have been a loose connection, but it didn't help).
-I've even replaced the Y-axis motor with a nema-17 that has a higher torque rating. The problem lessened, but is still there.
-When it skipps, it's always jumps toward the front or the printer, but not by enough to be a skipped tooth on the belt
-I always know when it happens because I can hear the motor make a KLANK sound, like it ran into something and skipped a step, but there is nothing there to stop it.

This is making me crazy, because I feel like I've checked or changed everything that could be causing this, and it won't go away. I have been watching it when it happes, and it seems completely randon, never in the same spot, or at the same time in a print, and I can't find anything that is binding. Do you guys have any ideas?

Thanks in advance.
Re: Y-axis slipping in only one dirrection
August 17, 2015 06:16PM
I had a similar problem and managed to solve it by reducing travel speed (not the print speed, just the speed at which the printer makes non-printing moves).

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Re: Y-axis slipping in only one dirrection
August 18, 2015 12:27AM
I had thought of that. But the problem just started out of nowhere, and it only effects one axis, and only in one direction. I would think that if it were moving too fast, it would have done it from the start, it would be on both axis, and even if it were only effecting the Y (because of the wieght of the bed), it should still be happening in both directoins (which it is not).

Who knows, though. I will probably try that next, I'm getting desperate. lol

Right now I've switched the X and Y axis connections, and I've got a long print going, waiting to see where it fails.

If it fails in the same direction as before, that will tell me it something with the Y axis motor or rails. If the shift starts happening on the other axis, that will tell me if it's something with the board or drivers (since my Y driver is actually controlling my X motor right now).
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