VPI Classic tweak

VPI does that for enthusiasts like me that don't have SDS,and no control over AC frequency, so we can obtain correct speed by changing belt position on the pulley, to go faster or slower.

Captain_winters,
I don't quite get how you reached the conclusion that "each position is a different diameter." I agree that each position might result in slightly different speeds, which two belts might or might not even out without the SDS. But why couldn't you dial it in with the SDS whatever the effect of using two belts? Regardless, it seems to me that the effect of using two belts would be more complicated than reducing it to an assertion of "fighting," assuming the belts are of identical length.

The actual diameter of each position is different. It allows enthusiasts without a SDS to dial in the speed as close as possible to 33 or 44. Check it out with the friekert app and test disk. It gets faster in one direction and slower in the other. Just by moving the position of the belt on the pulley. You can't notice it with the naked eye, but it is true.

Perhaps we're both have a different basis from which we extrapolate. I'm talking about a different belt position on the same speed grooves; there are three of those for 33 and three for 45. So 33 has three possible positions, each apparently resulting in some small speed variance at 33 rpm, which I accept. But to contend that the DIAMETER of each of those positions is different on the pulley seems to me to be quite a bit of a stretch. With tools you mentioned you can test the speed, but not the diameter. Using two belts on the top and the bottom 33 rpm pulley grooves should result in a net speed that should be able to be dialed in by the SDS. Both belts are subject to the same forces so the net speed should be perfectly stable.

How else could the speed be different? The pulley is machined to a different diameter at each of the pulley positions.