Boxford 260 VMC rebuild

[mike-f]

Right, if you’re thinking of picking up one of these mills, there are two key things to check before you part with your hard-earned cash:
Is the spindle running true? (Mine, er, wasn’t.)

How much backlash is lurking in the ball screws?

I’ll admit, I didn’t even think to check the spindle (not that it was important for the what machine cost). I’ve never come across a machine with such a wobbly one! The spindle itself was alright, maybe 0.005" out, but the Coventry Easy Change master holder fitted to it? A ridiculous 0.2mm off true. Pop a tool holder in, and it’s like watching a wonky spinning top. My first guess was a proper crash—someone giving it a right wallop. But I’m not convinced. The holder’s not shaped like it could bend easily, and the error was consistent along the taper. Feels like it was machined eccentric from the get-go. This being a late ‘80s model, ringing the manufacturer (still trading, mind you) for a refund was a bit optimistic.
By this point, I’d poured too much time into this project to chuck it in. So, my options? Shell out a few hundred pounds for a new master chuck body or try to salvage the dodgy one. Problem is, the body’s hardened to 55-58 RC, so turning it was out. Time for some workshop bodgery. I 3D-printed a mount for my Metabo die grinder, turned a mandrel on the lathe, and draped my trusty S&B Model A in as much protective cover as I could. Then, I set to cylindrical grinding the outer taper of the master chuck, this time true to the bore. The finish came out surprisingly decent, but I’m not keen on making a habit of it—my lathe didn’t sign up for this!
End result? Runout’s down to about 0.01mm, maybe a tad less. Not bad for a bit of shed engineering. Anyone else had to wrestle with a spindle horror show like this?




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