Grinding belt question: As a belt dulls, does it change grit size?

[jonwelder]

When I first bought a bunch of belts for my belt grinder, I got an assortment from 50 to 600 grit. I have found that I'm always out of course belts, and my fine belts don't get used much. As the belts dull, do they change grit, as in become finer? They seem to take longer to cut, and leave finer scratch marks. In the future, I'm going to order more of the course belts! (I hand sand and hand rub finish my blades after I ruff-grind, profile, and grind in the edge lines.) --jon

[Ed Caffrey]

No, belts don't change grit as they wear. What occurs is that the tops get worn or torn off the grit, and they become dull. This gives the illusion that they are getting finer, but don't believe it. Usually what happens is the dull grit builds up much more heat, and if your grinding on an already hardened and tempered blade, overheating and destroying the heat treat becomes a real possibility. I generally figure on one belt of each grit per knife blade. The reason I'm always running out of heavy grit belts is because I use them for a lot of other things besides blades. I think a person is money ahead if they purchase good quality grinding belts. The cheap belts are just that......cheap, and although you might think your saving money by buying them, your likely using 3-5 cheap belts where as you would only have to use one good quality belt. Things are different in each person's shop, and you may have to try several different types/brands before you find what you like. Personally I use Klingspoor CS411 in 50 for my heavy belts, Norton R823 in 120, Klingspoor LS309 in 220, and Norax in X30 (400 grit), X22 (600 grit), and X16 (1200 grit). I'm getting to where I kind of like the Norton "Hogger" in 50 grit, but it only comes in a Y weight backing, which is stiffer than I like to use.