My personal experiences with conventional V belts on machine tools are:
- conventional V belts are spliced. At every pass, the splice causes a "thump". On a lathe, this thump can show on surface finish. Poly-V belts (aka serpentine belts) on the other hand are endless, meaning that they have no splice and therefore no "thump" at each pass.
- conventional V belts have a memory. They will take a "set" if not used regularly. This set adds to vibration. This is less a problem with V belts that are ribbed on their back. I personally find that the very cheapest V belts take a set much quicker than good quality brand name belts. You get what you pay for. Tthe logos of the two belt makers "Gates" and "Great Wall" do not by accident look confusingly similar, but the products perform in every way very differently. Poly-V belts (aka serpentine belts) do not suffer from "set" even after long periods under tension of not being used.
- conventional V belts are made with rubber and perish over time. They are also to some degree affected by solvents and oils. In particular the presence of Ozone (Ozone is for generated by the arcing of brushed DC motors) will hasten the time it takes to perish. Poly-V belts are resistant to aging because they are made with Polyurethane.
- For any sort of machine tool, I do replace conventional V belts with link belts. I use Fenner V belts (from eBay seller Ohioblademan) and have found them to be A LOT quiter. And especially on the lathe to improve surface finish. Even on the humble 6x4 bandsaw I find the link belts run much smoother and no vibrations.
- In my lathe it would be necessary to remove the spindle to replace the V belt. That in itself is reason enough to upgrade to a link belt, as these can be installed without pulling the spindle.
- If designing a new drive for a lathe or mill drive conversion, I highly recommend to use Polybelts. I have converted my X3 mill to VFD and polybelt.
- for tractor implements, I found that in conventional shape V belts it is worth paying extra for Kevlar reinforced belts - these also use the more durable Polyurethane instead of rubber. Last longer and and stretch less. The downside is that cost is about 2-3 times higher than for conventional belts. You always only get what you pay for.