From DT Online
Tap Extractors are available which are designed to remove a broken tap from inside the threaded hole. They comprise a set of hardened steel ‘fingers’ which can be slid down inside the flutes of the broken tap and secured by sliding a collar down on to the top of the tapped hole. They can be successful if the broken tap is loose inside the hole (i.e. probably broken on the way out) but if tight, they may themselves break and make the situation worse! (especially if the tap broke at the bottom of a ‘blind’ hole).
Features and Applications
Other extraction methods include:
- Use a gas torch to Anneal to tap inside the hole then drill it out (provided that the workpiece can withstand this heat treatment).
- Drill out the hardened tap with a carbide tipped drill.
- Punch out the tap or use a punch to disintegrate it at the bottom of a ‘blind’ hole and remove the broken pieces.
- If possible, build up spots of weld on the top of the tap until it protrudes enough to be gripped and unscrewed with Vice Grips, for example.
- Industrially, a Spark Erosion technique can be used to ‘burn out’ the broken tap.
Note: Removing a broken tap is extremely difficult to achieve, whichever method is chosen, and there can be no guarantee of success. The only real solution is to take the utmost care when tapping a hole, expecially a ‘blind’ hole, to avoid the problem in the first place.
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