If the blind-hole depth and required full thread depth are the same, a standard tap is already in a difficult condition. The tap needs lead threads, chip space, and reversal clearance. When the drawing leaves no room, the process becomes sensitive and tool life usually suffers.
Why standard taps need extra depth
A cutting tap does not make full thread height at the first contact. Its chamfer or lead section gradually forms the thread. In a blind hole, that lead section needs room beyond the required full thread depth. Chips also need space, and the spindle needs a little safety margin during reversal.
Grinding the tap nose shorter may help reach closer to the bottom, but it increases chip load on fewer teeth. That can raise torque, weaken the edge, and make breakage more likely.
Process options
- Change the drawing to allow extra drill depth if the part design permits it.
- Use the shortest safe chamfer length rather than removing the lead blindly.
- Consider a forming tap only when the material is ductile and the tap-drill size is correct.
- Use thread milling when the thread size, machine, and tolerance make it practical.
- Review whether full thread depth is truly required all the way to the bottom.
For more background, see HEYI’s guide to tap chamfer length in blind holes and the thread mill selection guide.
When thread milling is safer
Thread milling can be useful when the part is expensive, the material is hard, or a broken tap would scrap the component. It also allows diameter correction with tool offsets. The tradeoff is that the machine must support helical interpolation, and cycle time may be longer than tapping.
Send the thread size, pitch, blind-hole depth, required full thread length, material, hardness, and machine type through HEYI’s RFQ page. That information determines whether a special tap, forming tap, or thread mill is the better starting point.