Some of the conditions which make it impractical to resharpen a tool bit are:
- Badly damaged (chipped) or burned bits.
- Bits that have been run too long in a dull state, causing excessive heat at the edge and subsequent local annealing of the bit alloy.
- Tool bits which have been resharpened several times and would require a complete new edge to be generated. Regrinding a new edge (behind the original edge) would make the tool bit too short to provide chip clearance with the holder.
Conditions which effect the number of times a bit can be resharpened include:
- Resharpening moves the cutting edge behind center, increasing the effective relief of the bevel bits which changes the cutting characteristics and tendency to dive (more noticeable on small diameter pipe and high bevel angles).
- Resharpening moves the cutting edge away from the original outside surface of the tool steel blank where the heat treat is optimum. The interior material of heat treated tool steels are softer then the outside surfaces therefore, will not wear as well.
- Resharpening decreases the grip length and or chip clearance with the holder. When chips start to jam into the holder, more cutting energy is required.