Check my pulley calculations

[JoeLee]

Not that bad, as mentioned you will likely need back idlers to increase wrap. You can run V-belts on the back side as long as they are not driving a load.
One may also buy 6 sided belts that drive from both faces. https://www.vbeltguys.com/products/b...yABEgIs2fD_BwE

I had a similar issue like this when I built an intermediate reduction for my drill press so I could turn the spindle at about 50 R's for hole sawing stainless.
I had to go from like a 9" dia. pulley to 3" on the spindle and 2" on the intermediate to 4" on the motor. Or the other way around, I can't remember. Both with very little space between pulleys. They both slipped some under the load needed to cut the stainless.
Traditional V belts didn't take the tight curve well and there wasn't enough belt contact around the smaller pulleys. I switched to the notched belts and that improved the grip quite a bit.
Those belts seemed a little softer too and they were a cut belt where the rubber contacted the pulley as opposed to a cloth wrapped belt.

JL............