Comments sought on new build: A CNC Router for RC Gliders and Planes

**njhussey** · 27-01-2014

Originally Posted by Jonathan

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.

The point I was cheekily making was that we get hung up on fine tolerances when your machine is perfectly good for cutting aluminium!

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.

99.9% sure ill epoxy it but will prob drill and tap the holes first. As you say the £45 or so for the epoxy is insignificant compared to the total price of the machine, its a no brainier. I'll still bolt the rails straight down though...just because!! ;)

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.

Again the rest of it was machined from nested parts on one sheet showing that with round rails on steel it's perfectly fine for cutting Ali!

**Jonathan** · 27-01-2014

Originally Posted by njhussey

Again the rest of it was machined from nested parts on one sheet showing that with round rails on steel it's perfectly fine for cutting Ali!

Within reason the accuracy of your rail mounting wont affect what the machine can cut - it affects how accurately the material is cut and how long the machine lasts.