K40 Y axis idler pulley

After a few months of work my K40 was acting up, not moving smoothly and the belt tension could not remedy this. I removed the whole laser gantry and found that the two pulleys on the Y axis were twisted and rubbing against the belt and the holder.

The reason is that the pulleys have a single 3x8x4 bearing in the middle and that's not enough to keep the bearing aligned.

You can buy replacement pulleys but in my case the axle had worn a groove in the middle and the pulley itself was actually fine. Couldn't find the axle and didn't want to install a flimsy arrangement again.

My solution was to replace the pulleys with printed pulleys that can hold 2 bearings for better support.

My pulleys are slightly narrower in the middle because my belt is only 8mm wide. Check yours before you print, you can always stretch the Z axis when you slice because the space between the arms of the holder is about 18mm, lots of space for expansion

You could drill the existing pulleys out to 8mm and insert bearings at each end, this would work fine but I wanted to keep them intact in case my idea wouldn't work.

FocusMiah has a similar system, they printed the holder too I but wasn't sure that would be strong enough, even with PLA, theirs was resin printed.
K40 y-axis belt tensioner and pulley replacement
Remove the gantry
693ZZ Bearings
K40 Laser Cutter Alignment
I ordered these metal pulleys complete with bearings but they arrived too late

In the end it works fine, I think a toothed pulley would be smoother and these you can buy or print.