Hello,
I'm studying the parameters of the G76 lathe thread cutting cycle today.
In the two line format, the P address indicates the total depth (or height) of thread, as a radius value.
I picked up from Peter Smid's CNC Programming Handbook, that there are two different constants to use when calculating the depth of external threads vs. internal threads.
For external thread depth (UN and ISO metric, 60 degree), one uses 0.61343/TPI.
For internal thread depth (UN and ISO metric, 60 degree), one use 0.54127/TPI.
I'm trying to locate some documentation on this 0.61343 figure. When I look at the thread form diagram's in Machinery's Handbook (p.1713 - 1714, Large Print), for example, they seem to suggest that the thread depth for both internal and external threads is 5/8ths of triangular height.
So if Pitch = 1, then triangular height from theoretical sharp point to sharp point = .5 / tan30 = .866025.
5/8 x .866025 = .541266.
However, 17/24 x .866025 = 0.61343, the constant for calculating external thread depths.
Where does this 17/24ths come from????? Does Machinery's Handbook, or some other documentation address it somewhere???