Measuring belt tension, squaring and calibration

CNC Machines Shapeoko
41

Thanks to Julien for updating the belt tension table in the first post of this thread.

Back in 2020 I only included tension for the 9mm belts as there were no (unmodified) machines running a 15mm width belt. Unfortunately the 15mm belt in addition to being wider, is heavier per unit length, which means it has a lower frequency than a 9mm belt for the same static tension.

This means that using the same frequencies as originally posted for 9mm belts on a machine with 15mm belts will likely overtension the belts quite a lot.

Apologies if this has caused anyone any issues but I only recently looked at the calculations again and realised how far out the table would be for 15mm belts.

I’ve seen no evidence yet that increasing belt tensions beyond the minimum required to match stepper forces improves performance, whilst we know that there are downsides, so here’s the updated table which includes the 15mm belts.

Select either 9mm or 15mm belt
Then whether you are measuring over 250mm or 500mm
Then pick a target tension, read across to the target frequency

e.g XXL machine measuring over 500mm with 15mm belts
Choose 89N → target frequency = 58Hz

Shapeoko Suggested Belt Tension 2.0
Shapeoko Suggested Belt Tension 2.01143×593 10.3 KB

I use about 95N static tension on my SO3 XXL and it is fine, calibrates well etc.

I have put the 150N in a warning red as this is likely more than enough to upset the stepper motors on the 15mm belt machines with their wider pulley providing greater leverage on the shaft.

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42

Hi Liam,

I have the Shapeoko Pro XXL and have downloaded a frequency measurement app for my phone.
If visualized as a ‘stringed instrument’, to which frequency shall I ‘tune’ the X axis belt and at which frequency shall I ‘tune’ the Y axis belt?

Thank you in advance,
Pablo

43

OK,

So assuming you have the 15mm belts on your Pro and you’re measuring over 500mm width between supports that’s 58Hz to 67Hz.

According to some smart people that’s a B1 or C2 note, does that help?

7 Likes
44

Yes It does. Thank you Liam.
Then, how do you ‘hit’ the note?

45

Not sure I properly understand the question, if you mean how does one pluck the belt to get the tone, here’s how I do it

If you mean how to actually tune the belt, I leave a turn or so on the M5 bolt on the belt tensioner to allow for some fine tuning, if there’s not enough there then I loosen it off and move the belt a tooth in or out.

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46

Thanks for the updated table with the 15mm belt values, it’s a big sanity saver.

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47

I will note that when I tension the belts, I find it easiest to do the initial connection with the machine at the center of all axes, then I’ll slowly/gently move it to one end, then power up and have someone pull on the gantry/carriage so as to take up the tension which makes it a bit easier to get the belt tightened up and secured, then power down, and repeat the process for the opposite end of the belt.