RHB, I have never scraped a lathe before. Done a fair old bit of engineering though. Bit limited in what I can do now thanks to ill health, so I might have to get a Sherline. The 17" length is good, but a bit of a worry about only 3 1/2" width. I will have to think about that. Still it is not likely to be this year if I go for the Sherline. With enough to get me started, maybe $2,500 including delivery and taxes? Gives me something to aim for next year though.
Yes, I did spend most of last night, including a good chunk of sleeping time, watching how to upgrade and do things on youtube. I even got a question answered I had always wondered. Using a flute with three cutting edges, you can drill a square hole (no, not a joke if you have never heard of this before), but thanks to YT, I now know that it IS possible to drill any n-sided hole by using a floating flute with n-1 edges to it. I have just realised that following that equation, a round hole must actually be considered to be a one-sided hole then.
OK, so maybe your timing is impeccable. Took me a week to decide between this scope and the 54, can you imagine if you had thrown the Chinese lathe at me as well? That smell of cooking would be my brain frying itself in indecision... Just think, you could stick a bit of kitchen foil to the chuck and shine a light at it. A simple detector circuit and I could use my new scope to calibrate the rpm. well, under no load condition anyway. I imagine the speed does vary if you try to remove too much material at once.
Come to think of it... If you used say strips of 1/2" adhesive tape and spaced them exactly 1/2" apart (might need to wrap the chuck in a layer or two of paper to make it an exact multiple of 1/2" strips), but you should get a pretty good 50% duty cycle square wave with either a focused laser, or IR, but with a slit over the detector. Doing that might help find the roughness in the way the chuck runs?