Two key things that I think will help: 1 - Each different size wheel comes with its own allen key. You have to use the correct Allen key for each one - so don't lose one thinking you can always use one of the others. Placing it in a new position on the rack allows you to increase the life of each wheel as the diamond coating wears out over time. Because stained glass is only about 3mm thick, you should have a few "cycles" of grinding wheels before they need to be replaced.