Lead grinding, also referred to as chamfer grinding, and is the most important feature of the tap that effects the cutting action. The lead length is most commonly referred to as “bottom” or “plug” and also less often “semi-bottom” and “taper”.
1.5 – 2 thd’s
2.5 – 3 thd’s
4 – 5 thd’s
7 – 8 thd’s
The lead is the only part of the tap that “cuts” threads. The longer the lead, the more tapped holes the tap can produce. For this reason it’s important to apply the proper length tap lead to the part being tapped.
Resharpening the Lead
Resharpening the lead of a tap requires regrinding the lead 2-3 threads up the tap to remove the worn, dull, and chipped threads, then cutting off the tap shortening it 2-3 threads.
Because the lead is the only part of the tap that cuts, this feature gives the tap its “sharpness” so it is very important for the lead to be ground properly, concentric, with equal relief, properly timed to each flute.
Another feature of the lead may be spiral point or gun point style. This is mostly included on plug style taps for tapping thru holes. The spiral point design is an additional grind that adds a shearing angle to reduce the torque required to cut threads while pushing the chips ahead of the tap.
TapSaver has specially designed, unique fixtures on dedicated grinders to control the lead grinding process on any type of thread cutting tap.