Work in progress - see changelog at the end of this summary
After playing around for my upcoming linear rail mod for the Prusa MK3 Bear Upgrade I needed a new belt holder for the y axis because of different distances from the belt to the idler and bed.
And I also was looking for a nice tensioner for the y-belt which doesn't shift the axis of a bearing or de-parallel-ises the belts or bring some torsion in - with no luck.
So I designed one myself and made it way stronger than the original one, perfectly aligned to the original Prusa idler and pulley design with a tensioning along the belt.
After getting reports about the tension screw of the former MK2 Version hits the pulley on the motor I redesigned the parts for those printers. As I don't have a MK2 I had to test it in a CAD model which seems to be fine now and the holder triggers the end-switch before hitting the pulley.
The belt path changed because of the less space in the MK2 version.
The sledge and the screw are now completely in the block
I made the sledge way a little wider (0.1mm) to counter the overhangs there.
Please make sure that the belt is on the sledge like shown in the picture with the red circle to maximise it's grip.
[2018/8/28] I will make a MK3 version similar to the MK2 version because it is smaller and stiffer (okay, less elegant maybe)
This Thing is a 3-parts design:
Please use the XXX for your printer
The _Cover is to prevent the belt skipping out of the teethed slots (6.2mm wide) and in the MK3-version also for the protecting the sledge it makes the whole thing even more rigid too.
The _Block is the main block which is screwed to the headbed-frog-thingie oriented like the original one
The _Sledge is the tension-mechanism, which slides into the block (see video on https://youtu.be/oqcmMYRy_z0)
Don't be confused by the dimensions on the pictures and the video - it's the version for my linear rail mod and different idlers. This Thing here is for the Original Prusa i3 MK3 / MK2S / MK2.5 with or without the fantastic Bear-Upgrade by pekcitron.
The STLs have the right orientation for printing - please don't change it because all the parts are optimised for high dimensional accuracy.
2 M3x20 Screws from the block side through the block and cover
2 M3 standard hex-nuts fits in the cover
1 M3x22 Screw for the (through) sledge (MK2S/MK2.5 M3x20)
1 M3 square nut which slides in the slot behind the sledge tunnel in the block
pretty easy, right? :-)
PS: I will add the STEPs and a GT3 belt version after my linear rail project is completed (could take some time)
Added MK2S / MK2.5 Parts - small refinement on _Cover
Small change to _Block for better dimensional accuracy on printing
Redesigned MK2S/MK2.5 Part because of screw hitting the pulley
reduced the height to gain more distance block->belt
the MK2S/MK2.5 parts are tested at real machines and working with the today's modifications
MK3 Version updated - moved the lower screw to avoid hitting the original MK3 alu frame
added some chamfers