@meddesign For some reason I was searching with the wrong keywords and coming up with not much, thanks for letting me know what to look for!
@gero Right now I am using a 105mm radius on the interior surface. I’ve found that having a smaller ring makes a really big difference in how smoothly the carriages move. When the ring is smaller the weight of the bricks pulling down has more mechanical advantage to turn the sled against the friction of moving the chain attachment carriages.
If you want to see the whole cad file it’s live here (so it will always be up to date):
@Keith Right now the chain attaches by passing through a square hole in the end of the carriage and is then held in place with a cotter pin. On the other side the two 30mm v-groove bearings are held in place with shoulder screws so that they can’t be over tightened which would add friction.