Even the ones with grit?
I ran into several references for putting compound on the cork belt with no grit, but nothing about the ones with grit.
SRJohnson taught me about cork belts a long time ago. He uses them today and learned about them while he worked with Ron Lovelass. Steve is a knife making legend.
I have never seen a cork belt without grit.
You can use them "plain" just like they are in the grits you want. They generate a lot of heat.
They also have a bit of cushion to them when you press hard into them. Like a softer contact wheel. This comes in handy, especially trying to smooth out a stubborn low spot.
A cork belt has huge, chunky bits of cork with embedded abrasive glued to a belt. The high spots need to be knocked down a bit so you run it hard with a scrap piece of steel jammed into it for a minute or two. This smooths it out a bit. The break in period is often exaggerated. A minute or two is all you need.
Abrasive granules need to break or fracture to expose sharp new edges. If the abrasive is embedded in cork, the granules break down quite a bit slower. You would think this is good but you end up with a dull belt so you press harder -- and generate even more heat. There is probably a special application that really benefits from using a pain cork belt but knife making is not one of them. There are better choices.
Cork belts come in several grits. I tend to use either 400 or 600 grit. I coat it with green chrome buff compound. It doesn't stick that well so you have to re-apply it often while using it. Run the belt fast enough to work but slow enough all your compound doesn't fly off. Generally, I will grind to 120 grit and then switch to a cork belt. If want a mirror finish, I will grind to around 400 and then switch to a cork belt (which green chrome).
It's messy. You will be covered in green dust. Don't breathe that in. Use a respirator.
Cork belts will last a couple years, even with heavy use. At some point the glue fails and then you need to replace them.
