When I built my kit I noticed something about the threaded rods. The lower section of one rod (which I put on the left side) has the thread crest's blunted while the rest have pointy or sharper crests. I can't tell if it was caused by grinding/sanding or pressing. The right threaded rod does not have this blunting. At the time I wondered if that was intentional? I thought maybe the rod was spun in a lathe to true it? Or maybe the crests were blunted purposely to help the nut move more freely on the rod? Or maybe I thought there was some intent to introduce 'slop' between the nut and the rod to reduce or eliminate and Z-wobble? I'm just guessing.
But I don't think the rod really needs straightening. Aside from seeming quite straight, since the threaded rod is loose at the top it should be able move if necessary. Nor do I think there would be any benefit to try inducing 'slop' into the fit of the threads because the flanks of the rod and bolt touch anyway and that determines how tight the fit is.
Anyway, this is something I need to address because each time the carriage is lowered to that point on the threaded rod there is a grinding/scraping sound (and indeed when I first ran the machine there were small flakes of brass that fell onto the top of the stepper motor). That makes me think there was/is a bur on rod threads. That brass nut must be worn now to some degree and it won't improve since the scraping continues.
So I'm wondering if I should just buy an M6 threaded rod to replace it? (I bought brass M6 nuts from eBay already.) And if so, is the pitch the same on most M6 rods I can find? I thought this one might be good:
Threaded Rod
I also thought to try to polish the thread valley by folding some very fine sandpaper to form an edge and press it into the threads while spinning the rod.
What do you folks think? I'd appreciate any feedback. Thanks!
