![]() ![]() ![]() You’ll get a series of samples where the app is “triggered” by the twang and a frequency reported figure out a reasonable average for the ‘good’ samples. Put the phone mic close to the belt and twang. The Gates app is meant to be used for lower frequencies on bicycle drive belts, it seems to get confused once it’s been open for a while so I close it and re-open it for each measurement. Now twang the belt, you should get a pretty clear tone without the slap of belt on rail or too much buzzing. Stick a small block or a ¼ inch cutter shank (thanks Julien) under the belt at each side of your marks, ensure you get the correct sides and that the distance of un-supported belt between the blocks is what you measured. Measure and mark a suitable length on your Aluminium extrusion rail, I’m starting 200mm from the end-plate and using 500mm length, 280mm seems a good number for the shorter rails of a regular or XL machine. To measure the tension using the belt tone method we need to have a known length of belt that we can produce a clean tone from when twanged. It’s free and measures in about the right range.īelt Twang Short and Long 1081×661 26.8 KB For this I’m using the Gates Carbon Drive belt tension app for bikes. The much easier way to measure tension on the belt is to twang it and measure the frequency of the twang. Knowing the tension modulus of the belt from the vendor data (Gates) or measurements of the specific belt (thanks to the_real_janderson see thread) we can then stick these numbers into a simple spreadsheet and get the belt static tension on our machine. With the luggage scale looped around the belt, pull the belt up until the top of the belt is flush with the top of the block, a finger is sufficient to test this, and record the measured “weight” as our measure for the Deflection Force F. With the belt in the normal position, mark the top of the belt on it and then measure the distance between the mark and the top of the block, that’s how far we will lift the belt from the normal position, our deflection d. On that mark place a block of about 25mm (1 inch) height for a long rail on an XXL or XL, or a block of about 10mm height for the short rail variant. Now mark the mid-point of the belt span between the drive pulley and tensioner, that’s about 450mm on the XXL. With the machine powered off push the X rail and Z carriage to their end-stops. The first method is to deflect the belt in the middle of a span and measure the deflection and force required, this is how belt tension gauges work on engines for Vee belts etc.īasic Belt Tension With Carriage 1081×301 13 KB Here’s a video showing how to do the measurements.Īlso, many thanks to for his assistance, suggestions and measurements from his machine. I will also not attempt to square or calibrate my machine in only one position, I’ll be checking back and front after balancing the Y belt tensions in future. I will be adding a belt twang to my regular machine checks, particularly to check the Y axes are balanced, I’ll also periodically take numbers with the phone app to check if my belts are going stretchy. I so far have no reason to believe that increasing belt tension reduces backlash or otherwise helps the machine, at least within the linear range of tension on the belt and the radial load acceptable to the stepper motors. ![]() Checking belt tension as part of maintenance will likely warn you when the reinforcing members in belt a starting to fail.Measuring belt tension is easy and you can do it with a cheap luggage scale or a free phone app.The results of persistent high radial load are fatigue failure (shaft snapping) and early bearing failure The belt tensions easily achieved with the unmodified Shapeoko tensioner clips are well above the recommended shaft radial loads for a normal NEMA23 stepper.You can fix this pretty easily by using the frequency tuning method, twanging the belts and tuning both Y axes to the same note. Belt tension means belt extension, if your Y belts aren’t equal tension your machine can’t be square and your Y steps per mm calibration can only be valid for one X position.I failed to find any quantitative data to use, so I went and started measuring and found that belt tension is quite important if you want to square and calibrate the machine effectively. How much you should have, how to check it and how it affects machine performance. The question of drive belt tension has been bugging me. A post about belt tension, how to measure it, what effect it has and why you need to manage belt tension in order to usefully calibrate and square the machine.Īs usual, no criticism of the machine here, in fact some quite clever design choices seem to have been made. ![]()
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