Do we still need the hardened steel shafts when choosing #IGUS / #tribo bushings? We could simply use aluminum round pipe but I am afraid that it is too bendy at reasonable OD (eg 10mm). Also, being extruded, it is as straight as extruded T-slot profiles.
What are your thoughts on this?
Given that steel is harder, stiffer, more wear-resistant, and cheaper than aluminum, what’s the case for using aluminum?
Ball bearings require hardened shafts with very smooth finish. Sliding bearings only need the shaft to be harder than the bearing, which is a given with polymer bearings. Igus bearings in particular work best with some micro-roughness, which sloughs off a layer of the bearing during initial break-in and coats the shaft with a dry film to provide mostly plastic-on-plastic contact. That doesn’t happen as much with electropolished-smooth shafts. Aluminum or ceramic surfaces are great for igus bearings. Unhardened steel is better for sintered bronze but ceramic-coated aluminum is also fine for sintered bronze.
Per unit cross-section, i.e. if your shaft diameter is fixed, denser metals are stiffer. Aluminum shafts should only be used if they have larger diameter than the equivalent steel shaft.
Hollow is fine, you don’t get much stiffness from the core of the shaft. A big tube is WAY stiffer than a shaft of the same weight.
@John_Bump
My case is availability. Smooth shaft of industrial grade can be found in the local hardware store but that’s bent all over and can’t be trusted (you can see that with the naked eye) while extruded aluminum round pipe can be found almost everywhere, is not very polished and is, like @Ryan_Carlyle said, it’s stiffer than the same diameter steel shaft.
@Ryan_Carlyle So you are saying that in my design I have 10mm steel shaft with LM10UU bearings, if I choose the #IGUS / #tribo route I should look for 10+mm hollow tube aluminum?
10mm hollow is less stiff than 10mm solid, and 10mm aluminum is less stiff than 10mm steel. 10mm hollow aluminum will be floppy. What hollow aluminum gets you is the ability to go up to something much bigger (like 20mm) without extreme weight or cost. A 20mm hollow aluminum pipe will be way stiffer and possibly still lighter than a 10mm solid steel rod.
Ball bearing rods should be induction-hardened and preferably chromed, which adds cost over a plain steel rod. Cheap unhardened steel rods are terrible for ball bearings but work totally fine for Igus bearings.
@Ryan_Carlyle Ok, got it, thanks. I don’t know if there are 20mm IGUS bushings or how much would those cost but anyway 20mm pipe will eat up lots of space in a 3D printer… maybe unhardened steel rods with IGUS bushings is a good way to go.
@shauki Are you saying that the round tubes aren’t same diameter along the tube? That would suck…but why? They are extruded just like T-slot…
+Peter van der Walt Cost is the main deterrent with V-slot.
Igus sells their’s own shafts. You can take better wrongful with these.