This came about while tinkering up a shade for a repurposed LED downlight:

It’s a 4 inch DWV pipe coupling I bored out to fit the LED housing, which was ever so slightly larger than the pipe OD.
Cutting it off required as much workspace as the poor little lathe had:

Ignore the toolpost handle across the top. What’s important: the cutoff blade poking out of the QCTP, above the orange carriage stop lock lever, extending just far enough to cut through the coupling’s wall before the compound hits the coupling. The compound slide is all the way out against the cross-slide DRO, rotated at the only angle putting the tool where it needs to be and clearing the end of the coupling.
It ended reasonably well:

But, in retrospect, was hideously bad practice. Next time, I’ll make a fixture to hold the fitting on a faceplate.