Nema 17 with a 4mm shaft? GT2 pulleys have a 5mm bore. Awesome...

All,

I'm in the process of building a prusa i3 using a single sheet aluminum frame. So far it's been a comedy of errors but that's cool because that's all part of the learning process. My latest hiccup is that I purchased 5 awesome Nema 17 motors but they have a 4mm shaft rather than the typical 5mm shaft. This poses a problem because every GT2 pulley that I can find has a 5mm bore. I'm not a savvy mechanic so please forgive my ignorance. Is it cool to torque the 5mm bore pulleys onto this shaft? Will it cause problems? Essentially I need to know where to go from here.

Thanks in advance

One thing I'd worry about is the pulleys rotating elliptically since the shaft is not centered in them. You could try to shim them with something thin like perhaps aluminum foil.

If that doesn't work, go here and buy 4mm bore pulleys: https://sdp-si.com

For plastic pulleys, I only see them in sizes up to 16 grooves (part number# A 6L51M016DF0604).. but that should work fine. They make larger ones in aluminum (up to 22 grooves), but they're also twice the price.

Thank you for that resource. The stepper motors I have currently have what appears to be a GT2 pulley of some sort already attached to them, though it only has 15 teeth. Also, it does not have a flange along the top so it seems as if the belt could slip off. The main problem is that the pulley is too far up the shaft. It's a pressed pulley so I cannot relocate the pulley further down the shaft. In order to make everything line up on the x axis I may just mount the motor with 6mm nylon spacers. I don't know if this is a bad idea or not. I'm going to give it a shot. Because it is a smaller pulley at least it has more torque and because it is a pressed pulley there is no chance it will slip. As far as the belt drifting off of the pulley... Well... I guess we'll see.

i have these exact motors, the pulley can be moved down the shaft if you have a press or makeshift it with a vice, make sure to support the end of the shaft though. I superglued some dimes onto the top of each pulley so the belts would drift off. also these things love to run on 24v. I use these on my corexy machine that i designed, they only take about 0.7 amps each so i run two on each axis off the same driver, and they are fast and torquey on 24v, no stalling. and they have heatsinks attached which is great.