Measuring Z belt tension on SO3 XL

I’ve been using my SO3 XL since 2017. Trying to get everything super dialed in, I just replaced the Z belt for the first time with these ones off amazon: 2GT-520-6. I tightened it to what I’d describe as “guitar string tight” based on the below post but it snapped at the very end of my first facing operation. Is there a more accurate way to measure z belt tension?

I would suggest sourcing an actual Gates belt — much better quality — should be available from BB Man., SDP/SI, and Texas Belting

Thanks Will - I’m having trouble finding a Gates GT2-520-6mm on any of those sites, do you have a link?

524 will work as well — might be enough adjustment for 516 or 528 to work.

Gotcha - Looks like SDP/SI is shipping 26 weeks out on the 524: Product | Designatronics Store | Stock Drive Products/Sterling Instrument. Shorter time for the 516 though.

When I get the new belt in, how do I make sure I’m giving it the right tension?

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Read this excellent thread by @LiamN.


I’ve used belts from this supplier before

They’re not bad at all, not the OEM Gates belt but I’ve used quite a few from Powge and they’ve been well made and I’ve not been able to measure any deviation from pitch.

If you really want to improve the overall performance of the machine, if you have the funds available, I’d recommend swapping out the belt Z for the Z Plus. That and bolting down the baseboard of the machine are the two biggest value for money improvements on the 3 XL & XXL in my opinion.



Thanks @BrokenEndmill and @LiamN . I read through the above linked thread on tensioning when I was getting my X and Y calibrated, hugely helpful!

I may have missed it, but I don’t see the same specific measurements for the Z axis, correct? I see that video from Winston below though, looks like he plucks the Z axis and I can just try to do something roughly the same as that.

I’d love the Z axis upgrade. Maybe once I feel I’ve graduated my current setup I’ll be able to make the investment.

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Ages ago, we noted the pitch we were getting on the Z-axis belt using a guitar tuner, but I can’t recall which specific pitch range folks were achieving.

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If you have a belt-driven Z, you could try making a post on the forum, asking if anyone has a Z-Plus gathering dust.


I didn’t measure the belt Z as I’d already upgraded to HDZ sorry.

I could probably break out the spreadsheet and work something out when I get back to the same country as my Shapeoko if that helps.

Honestly though, if you get a mid pitch from the belt you’ll be in the ballpark at that length, it’s short belt with a lot of pulley wraparound so if you get a twang there’s no real slack, if it’s too loose it will jump teeth and you’ll really notice that.


Thanks all for your help. On further inspection, it looks like my Z belt did not break, just came loose because someone (me) forgot to tighten the nut on the lower pulley after setting the tension with the tension screw.

@LiamN if you’re interested in breaking out the spreadsheet I would definitely use that information, but no sweat if you don’t. Between your comments above and Winston’s video on the subject, I suspect I can get it close enough just by eyeballing it.

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