I was talking yesterday to my godson, in training as a luthier, about your project… Got me thinking.
Would your design work if you used 12mm precision ground silver steel / tool steel rod through to whatever bearings/bushings you have intended, and then threaded the ends with a die to take a nut?
I’m not suggesting you make the change now, but if you find out that runout from the M12 allthread is too high in practice, then if your design allows you to make that substitution to improve runout, it will be overall cheaper than starting over.
Separately, a source of grippy rollers is dead laminating machines. The laminating machines heat the rollers up and run them top and bottom, but you could repurpose them. (I have two such rollers sitting around waiting to be reused in some project from my first laminator failing…) If you have thrift shops handy, you might find a $5 source of rollers at one.
I cringe every time I see someone show or mention using AllThread for axles without bearings. Spinning metal on top of threads is bad enough but plastic on threads is great if you’re wanting a larger and larger hole in your plastic.
The OP seemed adverse to purchasing taps and dies since it’s been the obvious fix for his inner thread problem and even the cheapest of taps would work on plastic.
@dougl to be clear, @NotTheMama initially expressed concern that taps would reduce precision.
I haven’t seen anywhere here a reference to not using bearings. I think you are maybe making some unwarranted assumptions.
ah, I guess I missed that. Was pretty lucky he found the exact tap he needed and it worked.
Yes, since I didn’t recall seeing bearings mentioned it was calculated that there were none. AllThread is great for structure and such but all too often I see maker projects using it for an axle which even greased really isn’t really a good idea unless just a prototype setup.
It seems that my project has sparked your interest (I appreciate it) - I hope that these pictures make things clearer - Note the 12mm smooth steel axle going through flanged bearings (hidden from view, inside the laminated timber blocks) and the Green PLA 3D printed hubs. There are four of these, spread evenly inside the cylinder.
I tried a few different designs for the hub locks, and settled on grub screws, but I am not entirely pleased with that. For the infeed and outfeed rollers I would like to try threaded hubs with lock nuts. Mainly because I have 2m of M12 all thread in my workshop that I would like to use for something. I intend to make some spacers and have the M12 axle run on bearings as well.
Thank you for the interest - Perhaps you can PM me if you want to discuss the sander design further.
@dougl You need not cringe on my account.
The sanding drum has a 12 mm steel rod axle and runs on flanged bearings
I am using M12 all thread for the in/outfeed rollers because that’s what I have lying around in my workshop… It too will run on bearings after fitting spacers. There are other reasons why I want to use the M12 all thread and threaded hubs.
Using a drill press to increase the diameter of the hole in the hubs those holes acentric and introduced wobble. I don’t expect that this will be a problem when using the tap to increase the tolerance of the M12 thread.
The subject of the OP is that my parts are precise in every dimension except for holes and threads. I would still be interested in having my holes and threads print exactly as I draw them on FreeCAD without resulting to fudging and trial and error, but it seems that achieving that is a lot more work than it’s worth.
Thanks for sharing more about the sander! If you ever feel like sharing more about that design (perhaps in #woodcraft:woodworking?) that would be interesting. I don’t go do DMs; I invest my time running this site to make ideas available to others.
I am guessing that the infeed and outfeed rollers will be spring loaded? In which case slight runout won’t have any impact in any case…
Yes, perhaps I will - The only reason I suggested a DM is that the last few posts were off topic. There are 100’s of videos on how to make a sander, but none that I’ve seen use 3D printed parts and none feature in/outfeed rollers
Correct! Pressing down on bearings sliding on a vertical track.
Cool! No pressure to share, only welcome opportunity if you’d enjoy sharing.