To minimize tapping problems and lengthen tool life, use the largest drill possible to produce a minor diameter that will result in the lowest percentage of full thread consistent with adequate strength. A minor diameter that provides a 55% to 65% thread is sufficient for most requirements, but in some cases a higher percentage of thread may be necessary to conform with the minor diameter limits of the thread class specified.
|
Suggested Percentage of Full Thread in Tapped Holes |
||||
Material
|
*Deep Hole
Tapping |
Average
Commercial Work |
Thin Sheet
Stock or Stamping |
|
Free
Cutting |
Aluminum
Brass Bronze Cast Iron Copper Mild Steel Tool Steel |
60%-70%
|
65%-70%
|
75%-85%
|
Hard
or Tough |
Cast Steel
Drop Forging Monel Metal Nickel Steel Stainless Steel |
55%-65%
|
60%-70%
|
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