Belt Tension Calibration

my printer manufacturer recommends belt tension calibration every 15 days ( seems it should be by actual printer usage rather than days; e.g., every 100 print hours, anyway…);
a few minutes internet research yielded an unpleasant surprise;
seems the common theme was to listen for the ‘right tone’ when twanging the belt;
surely there is a better way than that;
the printer i am most concerned about is a delta printer and it’s 3 vertical belts ; this type of printer is fixed-bed, no sling-bed;
since i doubt the belts ever get tighter through usage it looks like they would only get looser;
so all the adjustments would be to tighten the belt tensions;
i use that delta printer a lot and it is well past time to address the belt tightening;
but how much ?
my ideal solution might be to turn the adjustment knobs 1/2 turn or something like that ; each time the same, each belt the same;
what does a too loose belt do to the print ? can whatever that behavior might be be the indicator that it is time to tighten the belt (s) ?
thoughts ?

Well, I suppose the ideal way would be to have load cell built into the tensioner. Then a person could dial in the belt to exactly the right tension. What that tension is in lbs/kg/whatever, I couldn’t tell you.

It seems that it would be most important, on a delta printer, to have the same amount of tension on each belt. Possibly a gauge of some kind could be fabricated to set the amount of tension. Anyone have ideas.

for me, I do it by feeling, I personally usually stop short of Twanging on the belts. If they make a guitar twang they are too tight.

The reality side of things is, Belts are there to move an object via the drive of the motor. with the least about of reasonable backlash.

If the belts are tight enough as to not allow them to slip on the drive gear, that’s really the absolute min.

Past that make the belt tight enough to that from the longest point between 2 points where the belts wrap around. If you use your finger to jam the belt path move the mobile object, (bed or head assembly) Rock it back and forth with moderate force, you should not see any deflection in the longest part of the belt.

If you apply more tension than that you are really just stretching out your belt and shortening its life. Not to mention putting an increased load on the idler bearings/ Stepper motor.

I’ve been using the frequency of the plucked belts for years to determine the correct tension. It’s the best way and I’ve seen machinists use it for 40+ years.

A good article describing it is here:

I use the “Sonic Tools” app on my iPhone for determining the frequency of the belt. I haven’t found a good tool that determines the single highest frequency being sampled, but with a sound spectrum displayed, you can generally do okay.

To make things easier, I position my gantry so that the belt length is 285mm long - then I’m looking for 100Hz.

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Personally I have tensioned enough belts that I can just do it by feel.

There should be a little bit of give in the belt but they also shouldn’t be loose. I know that may not be super helpful but it is a little bit about getting the feel for how it should go.

There is a great video from Chep which I have linked down below where he investigates what happens when your belts are too loose, basically it just makes your prints look very sloppy. Personally I don’t tighten my belts up very much, I am kind of the mindset that I will set it and forget it, and then if I notice something is up I will take a look. So far I have only had to re-tighten the belts on a couple of printers, most of them end up staying pretty good. It can help if you invest in good quality belts and pulleys as they will be a little less prone to changing over the years.

Hopefully that’s helpful,