The first one took 1.5 hours to print. The move from M3 to M5 hardware created larger unsupported overhangs that printed worse, but sere still good enough to use.
The main difficulty I had was that the hole down the side is 30mm tall, and I don’t have an M5 tap with quite 30mm of cutting area. I ended up just pushing a few threads out of the way at one end to have threads all the way through, and it worked fine. PETG is a bit of a pain to tap. It really gums up in the flutes, and even with spiral flute taps I can only tap about 5–10mm at a time without clogging the flutes and having to back out and re-cut.
I haven’t tried a strength test. It looks good enough to print a second. At this point I plan to just install them both and test them.
The UHMWPE I’m using is impregnated with graphite, which is great for being slippery and even more self-lubricating, but also is… great at being extra slippery and hard to fix to the rod! Also the graphite gets all over my hands while I’m working with it.
The v bearings I bought are at best just barely big enough for the four strands (it’s doubled) that have to run through them. While I’m trying to make this work, I’m not sure I’d recommend it to the next person. I think it would have been smarter to use a couple of stepper motors to drive M8*2 lead screw, one motor at each end, and just have sensors/stops to tram them to deal with them getting slightly out of sync. At this point, there’s nothing actually preventing me from switching except curiosity as to whether this approach will work.
I note that my solution for the problem of terrible KP08 bearings would generalize to holding lead screws on the sides near the corners of the frame of the bed. So if this suspension approach ultimately fails, I’ll have some unused 8mm rod and exactly the eight extra 608 bearings I would need to move to a more conventional design.