I have some extra 200mm long, 9mm wide NSK rails and carriages from another postponed project. Yes, those are small and cute... I've wondered about using some of them for my z-axis. I have some 12in steel rails and steel V wheels I was planing to use, but those would add a lot of weight. I'm not sure it is necessary or ideal. These rails are super low profile (around 10mm high), and may end up saving a lot of weight and bulk if they are able to do a decent enough job. Two of these 9mm rails would have four carriages, each rated at (C 1490 C0 2150), which is about half the rating of a 608 bearing (C 3300 N) or similar to a 625 bearing ( C 1750) which are commonly used on Ox/shapeoko/diy style machines. Is there a very rough estimate for what loads are on the delrin wheels in vslot? I see on the polycarbonate wheels they list 25lbs and then 50lbs with "no noticeable deflection." I'm sure this is not the same as converting the 1490 to 335 lbs. That would be a breaking point rather than "no noticeable deflection." Are there "basic load ratings" for delrin wheels, or is the deflection measurement the part we should focus on rather than the listed stats? As another comparison, it seems SBR16uu bearing blocks are rated around 774 N and 1180 N, which is less than the tiny rail carriages I have. I assume the worst stress my machine will face is making relatively shallow passes at some aluminum 6061 at some point down the road. Steel V wheels on steel rails (and 6090 extrusion) will run the X and Y axes. Most jobs will be wood and acrylic. My motors are around 250oz nema 23 if that matters, using a gecko g540. The plates they will mount to are 9.5mm 6061 aluminum. My z-axis will have a makita RT0701C (around 4lbs) router. The final quick photo shows the red screw, with the black rails and carriages like I was planning. The green is an optional add-on that would add stiffness (didn't add the carriages, but four more green carriages). I'm not sure it is necessary. I thought I'd throw this out as an option before making any cuts. Thanks. Appreciate any guidance.