The critical point to bear in mind my old machine uses round rails on the X-axis, which tolerate a lot more misalignment than profile rails. The required tolerances go up a lot when you start using profile rails.


If you can get the rails to run smoothly without the epoxy, then that's probably fine for what you want to cut. The issue is it's hard to tell when a rail is misaligned by only a small amount, as this just applies a large quite large force to the bearings, but they can tolerate that temporarily. The problem is if you don't spot the slight change in smoothness caused by this, then your bearings could wear prematurely due to the increased load. Compare that to epoxy, where unless something goes seriously wrong it guarantees better accuracy and sufficient flatness. The £45 for epoxy is not much in the whole scheme of things when building a CNC router, so I'd strongly recommend it, although it's not mandatory if you can get the rails to run smoothly without.
Quote Originally Posted by JAZZCNC View Post
Excellent point and your 100% spot on.!!. . . . He's talking Bollocks.!! . . . . Measuring to those tolerences needs expensive highly calibrated equipment which I doubt he has either.

I'm not sure if I should dignify that with a response, but I will for now. Are you referring to the angular resolution I quoted? If so then it really should be obvious to you how I measured that from the photos.

Quote Originally Posted by njhussey View Post
However Jonathan's "Sufficiently strong" machine (a superb machine) was built with parts made (nested out of one large sheet of Ali) on a machine using supported round rail [...] Is that a chicken and egg situation??
The mounting surfaces for the Y rails were milled using the bridgeport mill at school, since it wasn't reasonable to expect the required accuracy from my machine.