Tapping Faults - Reasons for Tap Failure

   Tapping Faults of taps & common reasons for tap Failures by The Tap and Die Company :
 
Tap cuts Oversize:
 1.  Tap out of alignment with the hole or tap not running true
 2.  Feed pressure incorrect producing thin or deformed threads
 3.  Core hole too small:
 4.  Incorrect tap for the material
     eg. a) Cutting rake too great b) Incorrect thread relief c) Chamfer lead too short
 5.  Incorrect sharpening eg. chamfer relief uneven or excessive
 Tap Cutting Edges Chip:
 6.  Tap hitting bottom of a blind hole
 7.  Tap reversed carelessly
 8.   Lubrication lacking or of wrong quality
 9.   Material too hard or abrasive of the type of tap
  Rapid Tap Wear:
     Items 3, 8, 9,
 10. Speed too fast
 Poor Thread Finish:
     Items 3, 4, 8,
 11. Tap requires resharpening
  Tap Breaks:
     Items 1, 3, 4c, 5, 6, 7, 8, 9, 10, 11,
 12. Tap flutes blocked with swarf
 13. Blind hole: Below 4mm if tapping depth is more than 3/4” thread length, tap may break by chip clogging or  tap may break by hitting bottom
 14. Deep hole tapping: If tapping depth is more than thread length, tap may break by chip clogging
  15. In a punched hole the diameter of the hole reduces from top to bottom  hence material tend to grip the tap resulting in breakage of the tap
 16. The tap may break while reversing if jerk is given while reversing
 17. It is recommended to use proper coolant while tapping, as use of coolant reduces friction during tapping & reduces heat generation during tapping which subsequently reduces the property of welding build-up edge formation
 18. Improper drill size - only 'recommended tapping drills' (shown on lefthand side) should be used
 19. Tap may break during tapping, if cutting load is going beyond torsional strength of the tap ie. due to excessive torque.
Guideline for maximum torque that can be applied is shown below:

Size of TAP

Torque in
lbsforce x inch(distance)

BSW / BSF / ME

UNC / UNF / NS

Metric

BA

 

4

 

6

8

1/8

5, 1/8

3

 

12

 

6

3.5

5

17

5/32

5/32

4

4

23

 

8

 

 

25

11/64 , 3/16

10 , 3/16

4.5

3

45

13/64

 

5

 

57

 

 

 

2

62

7/32

12, 7/32

5.5

1

71

 

 

6

 

90

1/4

 

 

0

105

9/32

 

7

 

130

5/16

5/16

8

 

183

 

 

9

 

261

3/8

3/8

 

 

298

 

 

10

 

337

7/16

7/16

11

 

430

 

 

12

 

570

1/2

1/2

 

 

641


 The Tap and Die Company website has a lot of other very useful 'Technical’ Data & Information for you to view