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I finally got rid of the very annoying and varying short belt sloppiness on my Ultimaker.
This two-piece tensioner is simple, robust and it lets you adjust the belt tension with both precision.
It also protects your case from abusive screwing/unscrewing of the stepper bolts.
Disclaimer: please make sure never to over tighten your belts as it becomes very easy to do so... It will not make your prints look better and you most probably would ruin the belts and/or your bearings! Simply proceed with care as usual!
Update: if you want a spring-loaded tensioner, this variant may better be what you want: http://www.thingiverse.com/thing:40041
Update: added a version to hold the stepper motor by its 4 screws, in case you use 4 independent cylindrical spacers on the other side of the wall. It will help pulling it straight.
What you did
The usual fix is to unscrew the 4 bolts, push the motor downwards with a thumb and tighten the screws while keeping pressure. It is inefficient and annoying, and it even damages the printer plywood in the end!
What you will now do
Loosen the 4 stepper screws, adjust the tension by screwing/unscrewing the long vertical M3 bolt. Tighten the 4 screws moderately. Done :)
You can pinch the short belt with a finger while you adjust the tension. Hearing the sound is a nice way to set the proper and identical tension for the two axes (i.e. as is done with the long belts). Make sure NOT to over-tighten the belts else you'll ruin them and/or the bearings!
What you will need
Here are the parts for one tensioner:
How to proceed
The nylock nut is inserted longitudinally in a slightly conic hexagonal hole. Hence, you can print at any temperature and it will be OK: no hassle with lateral holes here!
I recommend you first screw the two pieces together tightly once to lock the nut in place, "deep" in the conic shape. Make sure the screw can slide freely on the head side (else drill the plastic)
Then, unscrew the long M3 nut so that it still protrudes by 2-3mm out of the nylock nut.
Attach the part that goes on the motor lower two screws (you need 25mm screws, the stock ones may be too short). Let the "fixed" part hang flat on the case for now.
While pushing slightly the motor downwards, mark the two holes (see the picture with the pen).
Remove the tensioner.
Making absolutely sure that you do not damage the cables within the case, drill the two 3mm holes at the marks (by the way, check that they are horizontal!)
Re-attach the tensioner to the stepper lower two screws, and firmly fix the lower part with two 10mm screws and regular nuts in the inside of the case.
About the files
I ued PLA, 0.4mm nozzle, 0.15mm layer height, 218ÃÂ°.
There are variants (while the two pieces come together in each STL).
One "downward version" show here has bigger holes on the stepper plate. This was made to insert two homemade washers made out of PTFE tube (6mm OD), that act as thermal insulators. I printed one of each and tested them in the long term. Update: really no need to worry about temperature here, the screw is not able to propagate enough heat to the PLA through the thick plywood layers even on very long & tricky prints.
The "upside" STL variant has m3 holes only. It inverts the orientation of the long M3 screw, so that you will be working from above and not from below. Thanks @am001 for the remark! Check the pictures and your onwn printer setup to choose which one suits you best.
The scad file is preconfigured with an upside adjustment screw and M3 support holes.
This thing is Attribution - Share Alike - Creative Commons. I will not and I cannot waive my moral rights on this thing whatever the Thingiverse bozos asks for
Robust and precise NEMA 17 steppers / belt tensioners by MoonCactus is licensed under the Creative Commons - Attribution license.
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