Printed from Kezuriba (kezuriba.net/en/troubles/rolltap-entry-burr/)

Burr or raised material at the entrance with a form (roll) tap

Tapping Tapping

Check first

Form tapping deforms the material plastically, so material rises toward the entrance

Try first

Chamfer the tap drill hole entrance
Use a smaller chamfer angle (e.g. 90° to 60°, recommended 60-70°) and a larger chamfer diameter (for 120°, tap outer diameter + 2P)

?Likely causes

Form tapping deforms the material plastically, so material rises toward the entranceAgreed by 2+ makers^[1][2]

✓Fixes

Setup

Chamfer the tap drill hole entranceAgreed by 2+ makers^[1][2]
Use a smaller chamfer angle (e.g. 90° to 60°, recommended 60-70°) and a larger chamfer diameter (for 120°, tap outer diameter + 2P)Agreed by 2+ makers^[1][2]

↔Related problems

Tap breaks Thread is loose (internal thread oversized; no-go gauge goes in)Thread will not go through (internal thread undersized; go gauge does not go in)Thread is torn or galled Tap teeth chip Tap wears quickly or welds

📚Sources

Causes and fixes are summarized in our own words from cutting-tool makers’ troubleshooting guides and technical data. “Agreed by 2+ makers” means two or more makers say the same thing.

OSG — How to suppress burrs at the hole entrance when using a form tap faq.osg.co.jp
Yamawa — Helpful Tips No.170: Countermeasures for entrance burrs on internal threads made with form taps yamawa.com