On Tue, 24 Jan 2012 16:09:34 -0500, you wrote:

>Not being able to imagine (I said limited brain, remember) how else they 
>cut tapered threads on a lathe in the old days, I expect the standard 
>specifications (ASME B1.20.1, fer instance) of the times would reflect this.

Hi Kent

Commercially taper threads were mostly bulk cut on repetition lathes
using die heads or fitted with taper turning attachments. (At least
where I worked) We made gas and water fittings of all types and sizes in
iron, brass, bronze and gunmetal.

Thread pitches on taper threads are measured exactly the same as
parallel threads - ie along the Z axis (CNC parlance). NOT along the
taper.

My CAM programs know this, and cut the threads accordingly -
unfortunately they turn out wrong.

On small NPT or BSP threads the error induced by incorrect application
of LinuxCNC's taper turning is small, but gets worse as the diameter and
taper increases. Certainly wouldn't pass inspection without correction
with my clients...

Steve Blackmore
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