Here’s a thread where a number of the custom designs by various forum members were discussed:
(but as I mentioned in the other thread, I’m with Anthony on the
part)
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I don’t know if I’m good or lucky, but I never really had belt tensioning issues.
On my SO3, I only really had to adjust tension a couple of times a year after temperature extremes. I replaced them once a year as preventative maintiance.
On my SO4, and 2 SOPros I found belt tensioning much easier. Especially on the SO4 and the small bolts to hold down the clips. The wider belts seem easier to feel for me. I haven’t had to adjust those machines after assembly, and they were all acquired at/ near initial release. The SOPro at work cuts plastic and aluminum a lot and still holds sub-0.010" tolerances.
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@neilferreri has a really nice design that lets you relieve the tension on the belts easily when your machine is not used for extended periods, then easily readjust.
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Tensioning the belt has been a frustrating experience for me too. After some trial and error, here is what I created to make it a pretty straightforward process.
I use a marker to know where I want the belt to remain relative to the tension clip. Securing the “clamp” keeps things in place while I tighten the screw.
I can slide the entire thing over enough to remove one screw. You can also just remove the bolts and plate to remove things.
Plates and flat screws came from Lowes. All in, maybe $5.
Finally, get a longer screw for the tension clip.
- ignore the marker lines as those were from a bunch of testing.
I actually was just tightening my belts. Last time I ran my Shapeoko it was freezing cold and now it is really hot in my garage. I am working on getting it insulated.
Funny enough one side was really easy to tension while the other was a pain. I think the screw is just too short in my case. Looks like per the assembly instructions it is a M5×12mm so I may pick up a M5×20mm and I imagine that would fix my struggles.
Don’t go too tight. Possibility of stretching the belt out and possibly breaking the stepper motor shaft.
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I’m measuring the tension it’s just for some reason I can’t get my left y belt very tight. I’m targeting ~56Hz frequency but I can only get it to 52Hz. Meanwhile I could get the right y belt to 60Hz pretty easily.
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Inspect your belt for damage/elongation of you can’t tighten it.
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What is the optimum Hz frequency for the Shapeoko Pro XXL?
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Same frustration here. Fiddling with the clip to make adjustments only to find out the belt slipped or the tension on the left/right axis is way off is frustrating.
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I’m targeting roughly 56Hz with a 20in span
Not to hijack, just a quick aside, as I am a new owner & getting near to building my PXL, can someone link me to an explanation of belt “hz” or explain it & how to measure it? Thanks! I am going to read the link above, maybe it covers “hz” aspect. In case it doesn’t, can someone explain about hz?
Edit: I see, measuring tone. I saw a guy who makes crazy cncs on youtube using a guitar tuner app on his belts.
I believe this was discussed in:
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Check out the post Will linked, if you’ve got any more questions then ask away.
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Just wanted to update that I bought two M5 x 16mm (the stock Shapeoko Pro comes with 12mm) and found it way easier to evenly tension my y belts. Not tensioning too high of course, just enough 
I just found it hard to get the thread started with the shorter screws
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The Pro is different than the SO3 in that there’s about an inch of space between the front/rear plates and any pulleys. That gives some room.
What about a simple clamp like this?
You’d have to trim your belt more, but you could get almost 15mm of tensioning.
I’ll upload STLs if anyone wants 'em.
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Here are the STLs if someone wants to try these out.
ClipBTM.stl (462.5 KB)
ClipTOP.stl (149.6 KB)
I’d print the big part with the M5 nut space facing up (no supports).
The bottom, I’d probably print with the M3 nut space down, but with light support there.
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I personally found that using a screw just 4mm longer solved my problems. I used gates app and measured frequency. Before I just found it hard to get adequate tension on one side, so a slightly longer screw made that much easier.
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I found it interesting that the holes for the screws themselves were tear shaped, not round. I had assumed they were meant to be positioned with that pointed up?