A sufficiently strong machine

[Jonathan]

Thank you for the comments so far.

Great machine and very informational build. I will implement some of your ideas on my next build, especially the system for oiling the bearings.

Please feel free to copy or develop the design, that's the general idea. You can have a better look at how it all goes together when I post the CAD models, which will be soon. Sasha's just updating them first, as for instance the model still shows the rails on aluminium strips not epoxy.

I am slightly curious about the ceramic bearing spindle. From my understanding, if you / god helps no to happen/ hit the spindle by accident on the table or a part, what would happen to the ceramic balls? You say there is an electric contact. Maybe only the lower pair is ceramic?

Yes that is a valid concern with ceramic bearing spindles, they are apparently more fragile. I'd come to the same conclusion with regards to which bearing are ceramic, but we're not keen on dismantling it to find out...

From where did you get that encoder for the spindle? Does your VFD support encoders?

eBay, like this one:
HEDS-5500#A06 - AVAGO TECHNOLOGIES - ENCODER, ROTARY, 500PPR, 2CH | Farnell United Kingdom
Part of the reason we had to put a PCB with the encoder was because the cheap one from eBay lacked the index pulse. If you're feeding the signal into the parallel port (e.g. to implement PID loop with linuxCNC) then the frequency needs to be reduced anyway. Sasha's just using the standard cheap Huanyang VFD.

Does the epoxy "self level" itself to a finish that doesn't need any more work at all? Just mount the linear rails?

Or was there more work involved?

Yes and no. In the pictures I posted you can see I had already drilled and tapped the holes in the frame when we decided to use epoxy. This meant that we had to plug them with bolts, covered in grease to stop them bonding, and use a countersink bit to remove the meniscus left around each bolt. To get a more complete surface for the rails to mount on you could leave the drilling and tapping until after the epoxy has set, since as there is no glass in the epoxy it drills easily with standard HSS drills.
Apart from that, no there's nothing else involved - it's a really easy process compared to the other options.

"However if I made another one of these machines (I could be persuaded),"

How much would persuasion cost

The problem is not so much the cost, it's the fact I'm still at University so available time to make CNC routers is limited. It's hard to say exactly how much, as Sasha and I obtained a lot of the parts cheaply on eBay and I can't rely on doing that again, but as a very rough estimate I'd say £4k-£5k for everything. Maybe less, probably not more. I'll post the breakdown of the cost of the components in the first post soon, just looking for some of the invoices first.