BROACH SHARPENING
This section deals only with the sharpening of high-speed-steel broaches. Not only are they the most common broach types, but the other principal cutting edge, carbides, now are used in throwaway forms. The original grinding is the responsibility of the broach producer. Resharpening is the responsibility of the user, but the broach tool may be returned to the producer for resharpening in the producer's plant. With proper care, and use most broaches may be sharpened numerous times However, the high-speed tool-steels used in making broaches include some of the most difficult-to-grind steels known. For this reason it is not unusual for a second-choice tool steel (in terms of tool life) to be chosen over a slightly better steel if the first choice is extremely difficult to grind. This decision frequently arises with abrasion-resistant PM-4 or T-15 high speed tool steel. The choice of a less-abrasion-resistant grade that costs less to resharpen often ill more than offset any cost savings gained from the longer tool life of the PM-4 or T-15 tool.
Internal broaches
Internal broaches are sharpened by grinding them only on the face. Metal removal on the top of the teeth changes the dimensions of the broached surface. Grinding on the tool face requires a small grinding wheel inclined at an angle greater than the face angle because of the geometry involved. Internal broaches may be retapered to remove abrasion in some cases.
Surface broaches
Surface broaches normally are resharpened on the face, but may be reground on the top of the teeth if excessive wear lands exist. When this is done the original dimensions may be re-established by shimming the broach on its holder. Care also must be taken to regrind the gullet space to the original tooth depth so that adequate chip space is maintained. Chip breaker notches must be reground.