J4 TIMING HUB does not match with 84XL037 timing belt. Most of the 28 teeth of J4 TIMING HUB work fine. Only three or four teeth are not correct. I tried it with a higher belt tension but it doesn't get better.
Interesting; I have not seen this issue come up yet. @Ari Hant @Matt Carrier have you guys experienced this? do you have any pictures of how your belts aligned on the J4 timing hub?
I had a bit of hand finish do to poor finish on the hub, but the pitches matched
The belt fits well on the printed version as well as on the aluminum version
here you can see the issue on the right side (the white paper is only for a better contrast)
if i turn j4 timing hub 180° backwards then the issue moves to the left side. I marked this two places in one of the following pictures. The red line is for the right side and the blue line for the left.
I haven't built enough of it to properly test that built but it does seem like when rotating it in my hands with the belt it isn't going to grip properly. As I rotate it seems to come out of alignment.
I suspect with these being laser cut and no finish work the OD is probably slightly large and the faces and flanks need polished. As soon as I get my next batch I will certainly review with different belts as well as some finish work and I will get back to you.
I just received the next batch of parts. The belts fit well on this batch so I am unable to replicate the issue but I suspect variance in cutting equipment and materials. I would recommend using a nylon abrasive wheel along the width of the teeth, polishing not only the OD but the faces and flanks of the sprocket - removing any sharp corners should allow the belt to fit as intended.
https://anninrobotics.com/wp-content/uploads/2025/07/issue-J4-TIMING-HUB_6.avif
https://anninrobotics.com/wp-content/uploads/2025/07/issue-J4-TIMING-HUB_7.avif
