An accurate and repeatable way to measure belt deflection and thus determine the tension in your printer belts.

This project grew out of a mistake I made purchasing a "belt tensioner" from AliExpress for $20, which turned out to be just a cheap digital tire tread depth gauge and some (very poorly) printed parts with a few hair elastics as the "spring"... Suffice it to say, it was hot garbage as sold, but I was intent on making it useful.

Fast forward 3 weeks of design, I reverse engineered the main clip on part for the foot of the gauge, the rear slide clip and added some features:

• Now snap fits onto your gauge and has optional thru holes for permanent mounting with screws.
• Uses a compression spring for better reliability, repeatability.
• Rear slide clip has retention pin and screw for better mounting.
• Has a proper "normal" pin spacing of 50mm. (was 62.5 previously ?!?)
• Included STEP files for anyone who has a different fitting gauge and wants to make changes.

Hardware required is simple:

• M3x20 Socket Head Cap Screw (1)
• M3x10 SHCS (1) (+2 for optional permanent mounting)
• M3 hex nuts (as required)
• M5x20 steel pins (2)
• Compression spring (I used what I had, OD 14.25, 70mm long, 0.7mm wire, 14 turns) from an old medical device.

The trick is to find a spring that is just right; not too strong so as to damage the belts and still strong enough to return the slide reliably back to start consistantly.

UPDATE: With the meter zeroed out at the min travel (spring pulled back all the way) on a Voron V0.1 using 6mm Gates 2GT belts, I get a displacement of 8.6 to 9.0mm consistently on my deflect-o-meter. The position of where you poke the belt greatly affects your readings on a 6mm wide belt, so try to hit the middle if you can.
This equates to roughly 14.5-15.5 N of tension as measured by a U-508 sonic tension meter, which is the suggested max tension for this width of belt.

BTW I printed my parts in ABS and the design accommodates for some material shrink, so if you are using PLA be advised. (I don't do PLA, ever!! )