Nice job on the spreadsheet!
I have that same lathe (although branded Select instead of Enco), and its speed chart matches the 60 Hz values in your spreadsheet exactly. Trouble is, they're close, but not 100% correct.
Here's what I'm talking about. When you move the spindle belt from position C to position B, the speed will increase by some multiplier that depends on (and
only on) the relative diameters of the two 3-step pulleys. Likewise, when you move the belt from position C to position A, the speed will increase by some different multiplier that again depends only on the pulley diameters. None of these ratios have anything to do with the position of the motor belt or whether or not the back gear is engaged.
Now here's an abbreviated (and not nearly as pretty
) version of your spreadsheet that contains just the 60 Hz speeds.
In columns F and G I've calculated the ratios mentioned in the previous paragraph. If the speeds in the chart were all correct, the numbers in column F would all be the same, as would all the numbers in column G. But as you can see, they're not. They vary by lots more than you could explain by something like rounding error.
When I first discovered this on my lathe, I became suspicious of
all the numbers in the chart. Besides the obvious problem with the ratios, I wasn't sure if the motor pulleys might have been changed by a previous owner, or even if the motor itself was running at the intended speed. So rather than driving myself nuts trying to sort it all out, I just measured the actual spindle speeds and made a new chart:
I'm not sure if any of this actually matters in practice.
-- Russell Mac