Trucks: I can't remember in which thread we talked about using glass bead bearings, but I do intend to try it, at least. So I bought ~6000 #15/0 beads last week, which costs no where near what you might guess it would. ~$10 US, including the four bucks for shipping.
IF it works, that's enough right there for about 750 cars...so next I need to design (ez) and print up some basic truck side frames (N scale) which will hold the beads where I want them. Then try some different music wire axles to see how well various diameters roll...or don't roll enough to continue with the experiment. This is why I will probably want to (carefully)flatten the backside of the trucks, and maybe the inner truck frames as well. The idea is to "trap" the bearing beads between the two frames and with some room to float, if need be, rather than trap them firmly. I can see advantages to both ways, at least enough to try it both ways.
AFAI can tell, 15/0 are considered the smallest beads that are widely available, although I know much smaller and more precise bead bearings ARE available too..but certainly not at such a low price.
Drawings of 100 ton trucks in N show a general "bearing area" about 2mm across, give or take. 15/0 beads are supposed to be 1.5mm in diameter, but some sellers will measure them more vaguely and with a wider tolerance at around 2mm, which would probably make the whole idea unworkable as far as consistency goes.
However, Miyuki beads (bearings) are advertised as being very acurately dimensioned, and from what I've seen in blow up photos and these in the containers I have in hand, they really do look to be very consistent. With the naked eye, they are all ground with a "flat" on the outside, which could be useful for locating them in a fixed position (non-floating) should that work out well enough.
It's claimed the hole size is 0.7mm, and once I thread a bunch of them onto some sewing needles (which I can easily measure with a caliper), I'll know more about which music wire or other wire sizes to try first.
They come in a variety of colors too--I chose flat/matte black:
https://www.amazon.com/Miyuki-Round...=1688353316&sprefix=Miyuki+15,aps,123&sr=8-37
That's not where I got them, but I think those are the same beads.
Miyuki 15/0 beads seem to come in 3 shapes: Round, cylindrical, and...perhaps perfectly sized...round, but with a ground flat on the outside. I do think that outside grind does make them very consistent, where the round ones might vary a bit. The cylindrical beads seem to be longer (along the axis) which might be more inconsistent as far as the bearing surface is concerned. I could see that going either way, in terms of rolling resistance.
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So why even bother at all? At some point I'm just curious to find out if they work better than conventional delrin trucks at all. There are a bunch of other possibilities too, but for now I'll leave it at that.