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PLA Bushings bind in XY axis

Posted by Andersl 
PLA Bushings bind in XY axis
February 11, 2016 06:11AM
Hi,

I'm slowly assembling my metric Tantillus build (after willworkforplastic's repo). Everything has gone well until now when I try to assemble the XY axis.

I get severe binding in my PLA bushings, they run fine by hand but when I connect them with the cross bar they bind a lot getting into
a stick/slip style movement. I also notice that when I change directions of the axis by twisting the corresponding driving shaft the XY ends
bows a bit, there seems to be some very small slop between the printed bushing and the XY end. The bowing is probably caused by the stick/slip.

I tried to lubricate the rods etc but the binding is quite severe even when I put small twisting (perpendicular to rod axes) loads on the bushing by hand. I'm thinking about designing
new XY ends that uses bronze bushings instead but before I do that it would be nice to know if someone has any advice on this.

Thanks,
Anders
Re: PLA Bushings bind in XY axis
February 11, 2016 07:18AM
I'm not familiar with the dimensions of WWFP's metric build, but you might want to check on the thickness of the acrylic spacer in the carriage. On my first build, I had a 6mm carriage spacer - it should have been 3mm. It caused severe binding when assembled.

They're typically a little tight when you first build the machine, but nothing that you'd call 'binding'.
Re: PLA Bushings bind in XY axis
February 11, 2016 07:36AM
Hi,

I actually removed the carriage to eliminate its effect. I'm using a carriage from thingiverse made to accommodate E3D style hotends so the spacer is not used. Mine was also erroneously cut in 6mm acrylic by the AliExpress vendor.

I couldn't find any posts where this binding was as big of a problem as I seem to have. I'm thinking that maybe it's the very smooth chrome plating on the rods that cause the binding issues? I think for igus bearings they recommend anodized rod surfaces..

How important is it to have the rods perfectly squared up in your experience?

/Anders
Re: PLA Bushings bind in XY axis
February 13, 2016 12:46AM
Hello,

Squared rods is essential for good printed squared parts :-D
And of course if everything are squared, parallel with the tantillus (ultimaker, etc...) there is less friction with bush/rod and hard "point", so you can decreasing amps on your nema driver, and so have less noise, less heat, and better accel, speed.

So you MUST be able to move with your little finger the XY carriage when everything is in place (unless motor).

Regards.
Re: PLA Bushings bind in XY axis
February 13, 2016 08:25AM
Hi,

Thanks for the suggestions. When I leave out the cross bars it moves quite nicely so I think I need to reprint the XY ends with a higher quality in order to make sure that there is no twisting on the XY ends when I tighten down on the crossbars (the holes for the cross bars are not perfect now).
There seems to be some twisting going on now and it is the major cause of the stiff movement.
I was a bit unsure first on how easy it was supposed to be to move the carriage from the instructions but now its clear that I'm pretty far from the ideal.
Re: PLA Bushings bind in XY axis
February 14, 2016 05:10PM
FWIW...none of my three Tantillus' were that loose when built. After building them, I usually spent a couple days running test prints with each, tightening the cables, and squaring up the axis. It's an iterative process as the cable drives settle in and you tighten the slack on each cable.

As long as you can move the carriage back and forth (I usually have to press both sides of the rod to do so), you should be OK. Everything will loosen up over time, and you want to start with the ends tight so you get good X-Y resolution (no slop). The printer tends to square itself up as you iteratively tighten the cables.

I've never encountered increased noise, heat, nor problems with acceleration or speed when my three printers were somewhat out of square. Maybe I'm just lucky...
Re: PLA Bushings bind in XY axis
April 02, 2016 07:09AM
I finally found some time to put everything together. It seems I worried a bit too much about the axis being to stiff to move since it doesn't seem to affect the printers ability to print out some nice parts.
The main issue seems to be that when I printed the XY-ends the slicer put a layer change where the axis is screwed down causing it to not be square. I also printed it all pretty fast at 0.3 mm layer
height so I'll probably reprint those parts on the tantillus itself eventually.

I will post my build log in a separate thread soon.

Thanks for the input,
Anders
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