Here’s a question nobody’s asked: Is it even possible to injection mould the bushings with proper tolerances? A proper bushing will not have draft angles, which will make moulding difficult. It will also probably take a little trial-and-error to get the fit just right even if you can manage it. You need a tight on the Z axis in particular because you don’t have gravity preloading it in one direction, and the whole axis can shift back and forth within the bearing tolerance. A cantilever does give you some preloading, but also tends to magnify any play that’s left.
@Whosa_whatsis I was thinking the same thing, but I think it’s doable by molding two pieces in a split bushing. Then you just need to get the bushing radial thickness right, and the pocket tolerances will enforce the final ID tolerance.
We were talking about using pin gauges as the center- ridiculously exact and available in all sizes. The center pin will push out- we don’t need draft angle on center pins just on outside walls. The two part is exactly what we were the gong. We have around 7 molds under our belt now and have been injection molding for over a year… Brian mastered it right out of the gate and has made some ridiculously complex molds… This one we are talking about is super simple.
Btw- I do want to make a part that others can use… But it may end up being as small and light weight as possible which will not be a drop in replacement for LM bearings
If you make something super thin is it worth also making a shell to make it drop-in? Or do the tolerances get too annoying?
That’s an idea… A separate shell that carries the Delrin bushing and is exactly the same size / shape as LM bearings 
They do the same thing with some linear bushings, just a sleeve with the sliding material on the inside. Could cut costs and you could make a metal casing that would make them super stiff.
Might work to make an injection-molded female tapered carrier, and an injection-molded split bushing with male taper. Then you adjust preload with a screw or whatever that pushes the bushing into the carrier. Overcomes some of the tolerance issues and possibly even wear issues. But the taper would make it easy to overtighten.
You can mold the part with zero draft in the inner surface using a stripper plate instead of ejector pins. Just put lots of draft on the non critical surfaces.
@Ryan_Carlyle
shallow threads on the taper, and something like a watchmaker’s crab to adust?
@paul_wallich Could probably get quite clever with something along those lines.
We talked more and Brian made some drawings… He’s gravitating to a direct bolt on piece half the length of a bearing. 2 of them, spread out should do the trick. They have protruding slots to mate w flat metal plate and assist straightness.
First we test material, then do a test mold. Then design some new printers to utilize them- greatly simplifying our designs.
@Ryan_Carlyle
Does “quite” in that sentence mean “usefully” or “excessively”? I tend to overthink designs.
@paul_wallich It could be really effective, but I think the complexity might be too much for the application.