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Loss of X position

Posted by gerv 
Loss of X position
October 01, 2012 02:50PM

Thanks to 30 seconds of great advice from nop head on Sunday about various config parameters, I now have my Mendel90 extruding plastic :-) I'm trying to print the little Android test figure whose G code was provided on the build day (with the first few lines hacked to use ABS temperatures rather than PLA ones). However, I find that the printer is getting each layer in a different place in the X direction. Within a layer, everything is fine relative to itself, but as soon as it goes up a layer, it starts printing a bit to the left or right - a different amount each layer, sometimes almost nothing, sometimes up to 1.5cm. This makes for very messy prints :-)

The problem may also exist in the Y direction, but much less - maybe a few mm.

Anyone know why that might be?

I've tried tightening the X belt. It does seem a little loose (taut, but no note when plucked) but when I tighten it any more, the X motor gives up and can't move the X carriage. (Anyone know why _that_ might be? Rods not parallel?) However, if that were the problem, surely it would go wrong while doing a particular layer, not just when it moves the Z?

Re: Loss of X position
October 01, 2012 05:17PM
I've worked this out. I had a max acceleration value set too high. I reduced it, and have now managed to print my first piece! :-)

Re: Loss of X position
October 02, 2012 05:41PM
Gerv would you mind sharing your config parameters (including the max acceleration)? - I'm in the middle of doing my config (when real life stops getting in the way!)
Re: Loss of X position
October 03, 2012 01:57AM
Of course. My Marlin Configuration.h is attached to this post. Let me know if any part of it needs explaining.

Note that I've ported Nophead's changes to the latest Marlin, so this Configuration.h won't match the one on his fork. If there is interest, I could fork Marlin and publish it with those changes integrated.

Also, since I printed two decent-ish mini-Androids, I've been having trouble recently, so please don't think this file is perfect! Nophead produced an Android figure G-code file for the build weekend last weekend. I don't have his permission to redistribute it, but if he adds a note here saying it's OK, I'm very happy to. (I hacked it to have ABS instead of PLA temperatures.)

open | download - Configuration.h (12.2 KB)
Re: Loss of X position
October 03, 2012 04:10AM
Your pulleys probably slip on the motor axis. A little drop of glue might fix it.
Re: Loss of X position
October 03, 2012 04:22AM
Thanks for the config.h file Gerv. I'll have a look in more detail later today hopefully but it gives me something to check that I've not made any huge errors in mine!
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