6.25 OD on your counter shaft, and 3" OD on you motor, looks like "about" 1/2 size at the motor, in relation to the counter shaft.
My countershaft is good, I will have to see what it measures. I know there are 2 sizes on the countershaft.
Do you still have pretty good power at the spindle at say 1/2 speed?
Did you ever put a tach on the motor, are you getting 1750 RPM, or possible a little more?
I think the voltage is what limits the RPM. I will probably measure Voltage at full power for the heck of it.
I wonder if that motor can handle a little over voltage?
Actually my old motor (and pulley) are the 1/2" shaft/bore. I hate to bore it out in case I want to/need to put my old motor back on.
But I have some 5/8 pulley's around here.
I am actually wondering if I can just but 2 single pulley's face to face to make up a double pulley?
Then I could use both of my counter shaft pulley's.
I will have to try it.
I got to get busy on this, and a lot of things, having some motivation issues right now.
Here is the switches and POT in a Radio shack project box for the KBIC-120.
Cost about $8.00.
thought that was reasonable.
I got a label maker I have not used yet, but I will make some more labels for it.
I guess they say the tape for the label maker is expensive, but if you make you labels all together and cut them apart, you won't waste as much.
I don't know, I didn't fool with it yet.
IIRC it was a $30.00 maker, but I got it on sale for around $10.00 at lowes.