Critique my mini epoxy granite lathe build?

[Doddy]

Linear rails and carriages will work - but you know that.

You're adding a lot of unnecessary height to the cross/top slides and the resultant increase in height of the spindle above the bed. I'm probably talking out of my arse here but the force on a cutter in the top slide lathe are a lot more predictable than a mill - typically with just about a single vector - are there no more appropriate systems than square rail for this application? That said, if you have the rail already....

If you want to cut tapers, and reduce your overall height - look at existing taper attachments for lathes (you need to be able to decouple the cross slide from the screw). You can lose the compound with this.

My main agreement with Pippen though is the amount of back-drive. Even on my somewhat light-weight ML7 you need a carriage lock to avoid back-drive on the original acme thread (I've yet to assess this on a ball/belt/stepper combo). My main, main issue though is bed length. If you know that this is sufficient for your need then go for it, but I can't help but think that you're going to be limited to something not much more that 100mm Z travel once you've finished.

EDIT: Cold light of day: back-drive - not with the spilt nut engaged (hence acme thread) - my bad, disregard - I had to lock the carriage to avoid back-drive against the rack-and-pinion of the carriage position wheel.