I've been asked to do a little boring (or maybe a boring little...) job.... See attached pics for info.
Basically, it's a toothed belt pulley, it'll be used to drive a mechanism. I need to bore the centre hole out to 25mm. Unfortunately, the boss is smaller than that & will disappear, so I can't hold it on that. If I do this in the lathe, it'll have to be held on the outer rims. Couple of issues there: They're really thin, and subject to distortion (it's an aluminium pulley too, so REALLY susceptible to distortion), and the spacing looks like I can't get it to sit on the flats on my chuck, at least one rim will always be at some point on the V-shaped grooved "grips".
My thinking is: Get a couple of bits of plastic, screw them together, bore a hole in the centre to fit the OD of the main pulley surface. Then, somehow, hold the whole thing together & turn the OD round. Split them, put them around the pulley, and in theory I can clamp onto the plastic & have it basically concentric (a few thou runout shouldn't hurt, this isn't a precision mechanism); drill & bore.
...Or, I could put it on the milling machine, and do it that way; I can strap clamp it to the rotary table that's on there now, or just straight onto the bed (well, raised up a bit obvs). and drill/boring head it to size...
Unless there's a crafty trick I'm missing on the lathe? Let me know!
Cheers!
Ade.
PS: OD is approx 3-1/8", or 78mm for those who speak French.