CORE One Belt Tensioner with Adjustable Endstop

Background

There is some variablity in how the belt tensioners are installed in the Core One.  This can cause the axes to be ever so slightly out of square.  This part adds an adjustable stop on the right side allowing you to compensate for the variablity in the install.

Required materials

You must print this part out of Carbon Filled Polycarbonate as the original part is printed out of this material.  This requires a hardened nozzle.  You will also need one M3x18mm socket cap screw, which you should have in your printer's spares kit.  If you can't find an M3x18 anything between 12mm and 20mm long should work.

Print instructions

Download the latest PrusaSlicer and use the following settings:

• Print settings: 0.20mm STRUCTUAL
• Filament: PCCF (tested with Prusament)
• 15% Grid infill

Installation

Install an M3 x 18mm screw in the extra hole.  Screw it almost all the way in until the head is protruding about 1mm from the body.

Remove the top cover.  Back out the tensioner screw completely releaseing the pully assembly.

Release the 3 M3x30 screws retaining the right side tensioner and put the screws aside.

Install the idler pulley with the screw into the new right side tensioner block.

Install the right side tensioner assembly back into the printer with the 3 M3x30 screws.

Now tension the belts per the docs.  I prefer using the belt tuner in the Prusa app.  Now with the extruder still in the middle of the gantry pull it all the way forward til it hits the hard stops.  Now check for possible movement on either side like below:

Adjust the endstop screw so that the carriage meets the front stops at the same time.  If the gantry to loose on the right, tighten the endstop screw into the block.  If the left side moves back the endstop screw out a bit.

If you want to be even more square, use my Vernier skew test to find out how out of square you are.  After adjusting the belt tensions check and adjust the front endstop so that the gantry hits on both sides simulatneously again.  Repeat until you get to 0 on the skew test (or give up squinting at the gauge)

Source File:

https://cad.onshape.com/documents/ad59b5aa68e7abe5ff7af77a/w/c21e1b1ca3a9b17e6b83c245/e/0868537424c37b24c5f14d22

This file includes a re-creation of the left endstop, but it's so much more difficult to replace that I decided that a single adjustable endstop was good enough.