Foolproof belt tensioners needed

Yep. Though I am thinking of 3D printing a guide for aligning the holes properly.

Excellent idea. Maybe one that incorporates a steel drilling collar so the drill wouldn’t damage the plastic.

Possibly, though for three holes that might not really be necessary.

For three holes you only really need a locator for a centre punch so you can accurately place a centre drill for the initial cut.

Yep, and possibly a filing guide to keep from filing too much away. I would like to not scuff up my cross members.

This topic was automatically closed after 30 days. New replies are no longer allowed.

Just checking, did anyone do this with stock SO3 endplates yet (cut a slot in them like in post 8)?

(also @neilferreri and @LiamN )

I did my own version of this idea. I drilled 3 holes and then used a coping saw with a fine toothed blade and some cutting oil to finish the slot. I have some other parts that then attach to the belt. It would be easy to over tighten them with my setup though.


I think @AndyC may know something about this…


Great idea! Did it turn out ok?

It works okay, I don’t love it. I am probably going to change out the actual tensioner bit I made. My design is fiddly and can loosen itself. I think I am going to see if I can make a simpler version of the one @AndyC designed for the contest.

1 Like

Hopefully I can attach the design files here, so you can take them as-is, simplify them, or use them to help realise your own ideas. Am very pleased with what I made, they are simple(-ish) to make, really simple to fit and use, and have stayed at the tension I set despite some challenging tests to stress the machine a bit.
I have one fitted to each of Y1, Y2 and X axis (pics attached). My Z is at long last now HDZ, so without considering linear bearings and screws (likely hugely expensive), tuning my 3XL is now down to HD Eccentric nuts, re-visiting squaring and truing.
If you want to avoid bending sheet Aluminium, it would be possible to make the clamp ‘frame’ from a block and rotate it 90deg for profiling and hole boring.

Belt Tensioner Clamp Flat Profile Rev-2.dxf (1.1 MB)
Vectrics VCarve (527.8 KB)


I’ve asked a local laser-cut jobbing shop to quote for making some of the brackets and adjustment arms (Stainless 304) to see what sort of price ‘just buying some’ would come out at. Volume pricing is a different topic, but that realistically means someone setting up supply, or Carbide doing so as an option for those who are comfortable cutting/filing the appropriate slot in the ShapeOKO frames - maybe their own revision too to the frames ex-factory to support either option.

1 Like

Thank you for putting the files here! Great job!!

And did you ever hear back from the laser cut shop on price?

@downrazor11 Quote has come back, about $9 per frame (cut and folded), and $1.50 per ‘arm’. This leaves two ground pins at say $50c, HDPE cam say $1, two screws and nuts, say $1. All in about $15 in out of pocket costs. I would have to order 12 sets to get this price.

Not that I am looking to make a business out of this, but just looking at this if someone were to make these up… $15 plus labour likely to reach about $30 in all. Plus whatever profit is sought. So a set of 3 clamps would be about $60 plus profit.


So, after trying to help @TX_diy with his belt tensioning woes, I thought I’d revisit this. (sidenote: is belt tension THAT important?)
I am building (so slowly…thanks corona) an SO3 for my classroom. I had Y plates made that have a slot where the belts could exit.

I stayed up way too late last night (inspiration hits me when everyone else is asleep) and here’s what I came up with.

First, the base which is attached using the existing M5 tensioning clamp hole and one of the M6 extrusion mount holes.

Inside the base track will ride the tensioner clamp.

The belt will be clamped with M3 screws and this little thing holds the belt extremely well.
The clamp has captive nuts for the M3s, and an M5 nut on the back for tensioning.

Finally, a cap covers it all. To tension the belt, all you need to do is turn an M5 screw through the cap to pull the sliding clamp.

My prototype works really well.

Unfortunately, this method involves making a slot for your belt. Otherwise, it’s a pretty simple mod.


I drew something similar on a sketch pad today for the Shapeoko Pro, albeit with a different look, but with the same approach for tightening the belt :slight_smile:

I’d have to actually model it in Fusion to explain it and the hardware approach/bits.


Too bad there’s no slot in the plates. Seems like it’d take a bit more work to do that on a Pro.

1 Like

A jig would be needed to make a crude slot mortiser.