Y Axis Belt Tension System MK3 MK3s

Time to upgrade the Y axis.

I wanted a Y tension system that utilized a rod/dowell and idler vs a screw and idler/bearing and was easily accessible from the front of the machine rather than underneath the heatbed. Though not a remix I did use the idler well on the base from Ed's remix https://www.prusaprinters.org/prints/8317.

This tensioner uses a linear guide (details below)

The motor mount is a slight remix of https://www.prusaprinters.org/prints/8317.

Goals:

• Have the ability to adjust the Y tension without having to remove any parts from the machine or move the machine.
• Have a more stable motor mount.

What I did

• Designed a Y tensioner that has two (or three) printed parts, a dowell, base and holder . The system uses two M3 13mm coupling nuts attached to the frame via the stock M3 10mm bolts. The idler holder slips over the coupling nuts and the tension is set by 2 M3 14mm bolts that face the Y motor.
• On the MK3s the belt holder is also the tensioner. Not only is this redundant it could lead to issues having two tensioners on one belt so I Included the original belt holder STL from the MK3. If you are doing this mod on a MK3 then you can use the existing belt holder.
• Changed the depth of the screw set from 20 to 21mm on the long screws on the motor mount. I read a comment that someone needed to hack off the end of a bolt to make it fit.
• The race/spacer for the idler is there to center the idler on the rod and not used in the final assembly, I printed this at .2 100% infill as a hammer was involved to center it.

I opted to go with a toothless GT2-20 5mm Idler as I thought it might be a bit quieter than the toothed version. For the 24mm smooth rod to hold the idler I actually printed the rod at .1 100% infill with PETG and it works great and is a little quieter and smoother than the steel rod IMO Link to the steel rod is below if you want to use a metal rod instead of the printed one.

Up Next - my take on Y axis linear Rails!

• Here is the BOM.

https://amzn.to/3bCSFAG GT2 20T 5mm Toothless Idler in black (pack of 2)
https://amzn.to/2uF3NvW 5mm 24mm smooth steel rod (pack of 40) You need 1. Yep lots of leftovers.
https://amzn.to/39rXdrB M3 x 13mm coupling nut you need 2
https://amzn.to/31PTt0l Socket Head Assortment if you don't have these in your spare parts bag.
M3 x 10mm Socket Head Bolt (pack of 10) You need 5.
M3 x 14mm Socket Head Bolt you need 2
https://amzn.to/39rXdrB M3 x 13mm coupling nut you need 2

Print instructions

PETG 250/80
Prusa slicer 0.2 quality with the following changes
50% infill on the base and holder.
0.1 Detail 100% infill for the rod/dowell
0.2 100% infill for the race/spacer

YMMV