issues with 16 tooth drive pulleys

Hi Everyone! I’m building my own version of a lowrider. I’ve got x and y working with endstops. The belts are GT2 10mm wide and the pulleys are 16 tooth with 5mm bore for the NEMA17 steppers. I’ve written some test gcode to exercise the x and y. It always starts by homing x and y first. At the end of any given test the gcode returns to x and y to zero position. After running tests several times I see from the LEDs on the endstops that I don’t quite get back to zero, which tells me the pulley has started slipping. Checking the pulleys I find the screws are a little loose. Tightening up the screws solves the problem, but they don’t stay tight. The set screws don’t seem to have consistent inside measurements. Ryan told me the small 16 tooth pulleys use a 1.5mm set screw. The allen wrench fits well with some of the set screws and I can tighten them well. On others the set screw head seems to “strip” and I can’t really tighten them beyond a certain point without destroying the screw head completely! I have another set of allen wrenches by a different manufacturer and I get the same results, so the culprit really seems to be poor quality set screws. I’m wondering what others have experienced. Did I perhaps get a bad batch? Or, are the little set screws just too small for the job? Should I go to a larger pulley with a larger set screw? Thanks!!

They should not take very much force at all.

To use a dual set screw system you tighten the flat first, making sure it is actually on the flat, then the rounded side. Use blue loctite if you are having issues.

The only time they come loose is usually doing that in the wrong order or not getting it really flat on the flat.

That’s exactly how I’ve been installing them. I’ve got pulley (out of 3) that tightened up perfectly and has never loosened. The other two loosen up over time. I’ve been very careful to make sure the Allen wrench is inserted straight into the set screw and to not over tighten, but some of the screw heads just don’t fit snug onto the wrench. I’ll use blue loctite next time and let you know how that works.


I bought a package of metric set screws on amazon a while back for not that much. I haven’t had this problem with my pulleys, but if you’re worried, they aren’t hard to get.

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I was just looking on ebay for those, and it gave me an idea! I found some short stainless steel screws in my junk box, 3mm, that fit the pulleys. They have a much bigger hex cap of course so I was able to use a much larger wrench to really tighten them down! They ain’t coming loose now!

They look a little goofy, but sure work well!


I replaced the stock grub screws with higher quality versions from a local industrial hardware supplier. The stock screws strip too easily (inner hex pattern, not the thread). I also used blue Loctite when I swapped them out.

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