Looking for feedback on plan for CNC router out of welded steel tubing

[Kitwn]

Kit, thank you very much for you reply!

I actually have the same idea that instead of ruining the aluminium plates directly, I'll first build a mockup from plywood. My idea to fix the overlapping problem is to just use counter bored holes, so the bolt heads of the bearings are below the surface. Is this bad idea? I'm not sure how to drill counter bored holes, maybe with a router?

The problem is how do you get at the bolt heads which are underneath the bearing you've just fitted

You will need counterbores if using two plates as well since the plates must fit flush. But if you make the plywood mock-up first ( with badly drilled counterbores that will be adequate if not neat) you will then have a fully functioning CNC router to do the job for you. Yay!!

If you can find aluminium profile at the price Andy is quoting then that's the way to go. If any of our Australian readers know of a local source of profile at the 50 quid ($90 AUD) price point Andy mentioned I'd love to hear from you. Here in remote Western Australia I got a quote for 2 of 900mm pieces of 120 x 80 mm heavy duty profile which came to $638 AUD inc delivery. That's about 340 GBP or 390 EUR. Slightly more expensive than the steel I managed to scavenge off the local tip!

A quick look at Fred's website (BST Automation on AliExpres) for a price comparison on rails says that Chinese unbranded 15mm profile rails and bearings cost about 50% more than 16mm SBR and the preferred Hi-Win brand are about 150% more. You said this was a budget project but there's always the balance between saving money now against not having to spend yet more money in future to upgrade to something better. You can get SBR rails more cheaply on eBay but there's no guarantee of quality. Note that the profile rails are much less tolerant of uneven surfaces and other misalignments than SBR so the rest of the construction needs to be of a higher standard.

My machine is only intended for cutting wood and for reasons of cost and my uncertainty about accurate construction of the frame I went for cheap eBay SBR rails (20mm for the long X axis and 16mm for the Y) with the plan to upgrade to profile rails if the SBR proved inadequate for my future requirements.