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# the interpretation of AS8879

## the interpretation of AS8879

(OP)
AS8879
3.4.2.2 Flank Angle: The flank angle shall be 30 degrees. Flank angle variation shall not exceed a value equivalent to 40% of the pitch diameter tolerance.

how to relate angle in degree to pitch in inch?
thanks.

### RE: the interpretation of AS8879

SAE AS8879 is derived from original standard MIL-S-8879. Here is the section on Lead and flank angle (3.4.5.2 from Rev C):

The lead shall be the number of thread starts divided by the number of threads per inch. The flank angle shall be 30 degrees. The diameter equivalent of variations in lead (including helix variations), or flank angle, shall not exceed 0.4 of the total pitch diameter tolerance for each element individually.

### RE: the interpretation of AS8879

(OP)
i still do not get. say pitch diameter tolerance .005". 40% is .002". how to equivalent to degree/minute/second?
thanks.

### RE: the interpretation of AS8879

(OP)
TVP, thank you.
sorry for my stupidity.
1-12-UNJF-3B. pitch diameter .9459/.9516, 40% of this tolerance is .0023".
1-12 has pitch (p) .08333.
from 3.4 of the booklet, .0023 = .0091 * .08333 * (FLANK ANGLE DELTA)
IT RESULTS delta flank angle 3.05 degrees !
i do not know where i did wrong.
even, it results a meaningful small number, how it is measured in industry?
thanks again.

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