Whenever I get in touch with a project like the MPCNC, I start thinking about modifications, variations, building on the given material. So, to get things verbally rolling, I first purchased a couple of stainless steel tubes, polished, from my favourite metal store.
I found that the tube diameter a) is not perfectly circular and b) varies between 25.00 and 24.92 mm, according to my calipers.
So, I am seeking an answer to the question how the mechanistry of the MPCNC interacts with such imperfections - do the roller bearings’ holders represent some sort of elastic mounts putting some pressure/tension on the bearings’ axes?
What are acceptable tolerances? I can imagine that other hardware is even less straight than the polished VA tubes (2mm wall thinckness, btw).
I also thought about replacing the set of rollers by an axial bearing, like the LM8UU which is heavily usd by reprappers. There are larger variants, even an LM25UU exists, and igus offers a plastic one designed for heavy duty loads. Single pieces of that sell for about 8 Euros.
The LM25UU puts pretty close demands on the diameter tolerance of the carrier tube. Smaller diameters will work, of course, but rattle more or less. How will the 608s behave? Are they mounted under enough mechanical tension to at least minimize lateral mobility?
More questions to be expected…