Gang,
Recently had to bore a taper (for a homemade battery terminal I'm
making for an auto battery) and got involved in trying to determine
the angle (in degrees) that I would have to set the compound on my
lathe.
In looking through the Machinery Handbook, "Rule: Divide the taper in
inches per foot by 24, find the angle corresponding to the quotient,
in a table of tangents, and double this angle". Example : taper of
1-1/2 inches per foot, divided by 24 = .0625. The angle whose tangent
is .0625 = 3 degrees 35 minutes nearly, then 3 degrees 35 minutes
multiplied by 2 results in 7 degrees 10 minutes.
Now, I realize the last part (multiplying by two) is dropped for
turning on the lathe as I don't need the included angle - only the
angle from the centerline of the part.... but my question is "Who
came up with the number

___24___? ? Is this some mystical number that just works or is there actually a relationship? Thanks. (btw, the bored holes came out perfect). Ken.