How thick should I leave the cutting edge before heat treat?
This is a question like many others that is hard to answer. You first have to determine what use the knife will be for and then the type of grind the blade will have. Then the type of edge needs to be determined. As an example on the most copied knife ever, the Bob Loveless drop point hunter. Bob Leaves 25 thousanths for the edge prior to heat treat. This is a hollow ground stainless steel blade that is designed for hunting.
