Bught an interesting 1944 Monarch lathe 16x54

Don' please elaborate on "smaller motor and spindle held in big chuck". Sounds interesting. Ivan Vegvary.

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    Well ... lots of possible ways to do it. One would be a spindle which passes though the main spindle and is held in the large chuck. That one would be driven by an outboard motor which couples in through the back of the spindle.
    Another would be a spindle (and bearings) held in the big chuck with a pulley on the workpiece side of the big chuck, and with a belt going to a motor behind the bed -- and likely behind the headstock as well.
    In any case, you want to lock the spindle by engaging both back gears and direct drive (unless this is purely gears inside the headstock, in which case I would look for some form of spindle lock on the headstock. And interlock it so nobody can power up the main spindle, because that would beat the motor and the bed to death.
    Without seeing the lathe, I don't know what would work best -- and it would also be dependent on what parts you could find. For a really small setup, something like the spindle cartridge from a Unimat SL-1000 (goes for insane prices these days, because they are collector's items). For that, you would have to make a drive tube which threads onto the outside end of the Unmat spindle cartridge in place of the pulley and nut, and extends outside the far end of the main spindle. Install a bearing on the outboard end of the drive tube which is a nice fit inside the outboard end of the big spindle. This would then let you use some small three and four jaw chucks, and with creative work and the WW (watchmaker's) spindle for the Unimat, even really tiny collets.
    I wonder whether you could take the spindle cartridge out of a Taig lathe -- a little bigger than a Unimat SL-1000, and a lot more affordable, since it hasn't become a "Collector's Item".
    What you would lose would be any existing power feeds on the lathe, and have to come up with some other way to do those, too.
    Maybe mount a small cross-slide and compound on the big one, to give you finer feeds.
    Just some speculation. :-)
    Enjoy,         DoN.
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Until you need to do some small diameter work which case it'd be like feeding an infant with a backhoe instead of a spoon.
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