Oh, and about pressure. Finding the right pressure is a learning curve, too. It doesn't take a lot of pressure on a new belt. As the belt wears, you begin to compensate for a dull, badly cutting belt by pressing harder. This is where mistakes happen. When you find that you keep chasing your grind all over the place, chances are you are using too much pressure to overcome a belt that isn't cutting.
So, how do you know when a belt is too dull to cut? The answer to that will evolve over time. Right now, dull means that you seem to be making more heat than progress. When it seems like the piece is getting hot every time you make a pass or two, that belt is no good for bevels.
As you progress, you may determine that a belt is toast when you have to press more than usual to remove the metal you expect to remove on each pass. There will come a day when you make a pass and just don't like the way the finish looks and you'll grab a new belt.
All new knife makers cringe when changing belts. I used to feel physically ill when I changed belts. It seemed like everything I touched was costing me more money. In the beginning when money is tight, that's true. But once you start selling your knives, the cost of materials is part of the sale. The customer is paying for belts and you need to have more than enough cost built into the price. That's when your time is the only cost that counts.
Old belts can be used for handles and for rough grinding blanks and general grinding. All is not lost just because the belt isn't good enough to grind bevels.
