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Ultimaker Short Belt Tensioner

Tired of tightening the short timing belts so often? Here's the snap-on floating belt tensioner.

3D printer parts and enhancements

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The tightener can move freely along the belt. Flanges on the roller
parts keep the assembly from falling off. Attach small pieces of felt to
the faces touching the steppers or the walls if you encounter rattling
or rasping noises.

Hint: Save the nuts and glue the guide bar screws into one slider part.

Print at 0.1mm layer height, 1.2mm wall
thickness and 20% infill. Clean bores after printing to let the sliders
move smoothly along the guide bar screws. Tighten the roller screws to a
loose fit to let the ball bearings move freely. Check for
smooth-running of rollers and sliders before attaching the tighteners to
the belts.

Snap on the belt tighteners onto the short belts and
make sure the flanges are embracing the belts at the side facing the
walls. If the belt is too close to the wall, re-adjust the pulleys to
have 1-2mm clearance from the walls. The rollers should barely touch the
walls but not scratch them.

I received some feedback on concerns about adding a spring to the drive system, which could introduce negative effects on the system's dynamical properties. I generally agree, but I think these concerns do not apply here. The sprung system is not supported by the non-moving frame, that's the small but nice trick of this design. Directional changes of the belt movement will not cause the spring to be deflected and store/release energy. If one piece of the belt is tightening, the opposite part will loose the same way, so the tensioner assembly will slightly move laterally, but the spring will not see any deflection. There is no dynamics in the tensioner length at all, the spring just applies "static" stress to both belt parts symmetrically. Fixing one part of the tensioner body to the frame indeed would introduce ringing and overshooting on directional changes.

Update 2:
Minor changes to roller part. Flages extended to prevent tensioner occasionally falling off. Larger bore for screw head to fit an additional washer for reduced friction between the roller and the screw.

Materials and methods

2 x slider (printed part)
2 x roller (printed part)

- 2 ball bearings 10x6x3
- 2 screws M3x30
- 2 screws M3x16
- 2 nuts M3
- 2 nuts M3 self-locking or M3 + Loctite
- 1 tension spring 10mm (not too strong...)



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20c2f944d93975910cd24c4c76e9c75c?default=blank&size=40Ryan Lake added this to the Ultimaker Original+ Upgrade collection ago
6fe419e9d9e8a893bf30f7b9d92b1f68?default=blank&size=40kesjeff added this to the Ultimaker collection ago
Mini lisca mangaLisca added this to the ultimaker up's collection ago
Mini imagedevnull published this design ago