Tapping Threads

{Note: if anyone has a question, comment, or improvement please email or comment. New failure modes are especially welcome}

Tapping a Hole
Process Intent: (Wikipedia has a pretty good rundown of terminology)
Taps and dies are cutting tools used to create screw threads. A tap is used to cut the female portion of the mating pair (e.g. a nut or hole). A die is used to cut the male portion of the mating pair (e.g. a bolt). The process of cutting the threads in a hole is called "tapping" the hole.

Process Inputs:

• Drilled hole to correct depth
• Drilled hole to correct diameter
• No chips/swarf in hole
• Chamfer (needed?)
• Tap feed
• Tab speed (RPM)
• Lubrication
• Proper fixturing (position and stable)
• Material properties (for example, hardness. Also, porosity, inclusions)

Process Outputs:

• Threads to correct diameter
• Threads to correct depth
• Thread form

Potential Failure Modes:

• Threads not to depth of hole
• Thread diameter too narrow
• Thread diameter too wide
• Threads do not follow hole, misaligned
• Chip/Swarf in threads/hole
• Broken tap

Cause of Failure:

• Incorrect Tap
• Incorrect cutting speed
• Insufficient lubrication
• Incorrect position of part on fixture
• Worn tool Broken tool

Controls- Prevention:

• Tap identified
• Cycle count
• Cutting speed
• Torque- and process controlled machine
• Fixture design/ lock clamps? sesor?
• Drilled hole depth sufficiently deep ?

Controls- Detection:


Some interesting resources:

Know-how in thread tapping from Microtap
Tap and Die Terminology by tapdie.com
How to inspect internal threads by Eric H Johnson