Are you trying to "chase", or clean-up existing internal threads? Use a tap designed for the job at-hand.
When we at North American Tool are informed that a tap is to be used for " re-threading", another term for this task, we always recommend at tap with 0-3 degree Rake for the cutting edge.
Different Than Threading the First Time
When re-threading, very little material, if any, is being removed from the existing threads. It's possible that none of the substrate will be touched, especially when the need is