Hi All
How would one go about screwcutting??? on a lathe a curved thread is it just a matter of putting a feed of .0833 (12TPI) into a g2 or g3 and doing lots of small cuts. I have an encoder fitted to the spindle to synchronise the thread start.  Its a fusee for a clock that I am thinking of making.
Graham

Is there a need to make a matching nut to the curved section as shown on the drawing? IE; the threading is for decorative use only
You can cut thread along the profile using a G2 provided the spindle speed and feed rate is correct  for a single cut depth. Maybe one
can trick things some by having the G32 ( allow's use of the index ) start the threading upstream of the edge and then there is a change 
to the G2  with the same feedrate but would need to vary the G2 /G3 code for the different radius. My want to also try what LT would do
for the curved profile by varying the depth of cuts. Then one can always slave the spindle to the Z and try that route.
May be all wet .....interesting one ........maybe others will have some thoughts on doing it.

Have fun ....... ,
RICH

BTW, never tried cutting threads on a curved surface with the lathe ....but probably have some junk from my early turning days
that may look like it was done.......    
RICH

Hi Rich
The 2.5" rad on the drg. is where the 12tpi "thread" is machined. It is to take a drive cable from a spring drum of constant dia to the fusee so as the spring winds down the ratio between the two reduces to counteract the weakening of the spring.

Graham

Don't have any other thoughts on how to possibly do it. Wish ya luck....
RICH

Hi all
As the " thread " depth was only .020" with a .022" radius on a .045" wide parting off tool I managed to do it with a 0833" feed using G02 and starting the arc .5" before cutting metal. In brass it left a good finish with minimal polishing.
Graham