View Full Version : internal tapered threads

04-19-2003, 01:50 PM
Can an internal tapered thread be single point cut without a taper attachment? I got to thinking about this when I saw a picture of an old bench lathe with no leadscrew. Instead it had a driveshaft with a full lenghth slip yoke driving the compound leadscrew. The compound could be set parallel for straight threads or at any resonable angle for tapered threads. An interesting solution for cutting tapered threads.

04-19-2003, 11:44 PM
Maybe with a steady rest offset for the taper?

04-20-2003, 12:40 AM
I thought of that, but it seems it would have to be a special steady rest with provision to offset and pivot so that the jaws would make full contact with the work.

04-20-2003, 01:02 AM
what are you trying to make?

04-21-2003, 01:50 AM
I was just curious, no particular project in mind. I like to learn all the tricks I can in case something comes up though.

04-21-2003, 02:45 AM
How about cutting a normal thread, to part depth, then following that with a hand-held tool guided by a rest set to the taper angle? Clamp a stop on the tool to bear against the rest as a depth stop.

04-21-2003, 08:20 PM
we turn the tool upside down and cut away from the chuck with the spindle running backwards and hog it with the cross slide as it cuts out.

its called faking it.
not perfect but works fine!

Forrest Addy
04-21-2003, 09:15 PM
No taper attachment?

Try this golden oldie: to cut tapered threads (or tapers) set a parallel to the taper half angle and follow it manually by dialing the cross slide in (or out) with a dial indicator as the tool cuts the thread.

In the case of pipe threads the taper half angle is about 1 3/4 degrees. Clamp the parallel to the ways where a dial indicator mounted someplace on the cross slide can get at it. Set the angle, practice the moves before you cut, and start making chips.

Tapered pipe threads don't have to be perfect but need only reasonable fit. The heavy torque used to tighten tapered pipe threads and the material's ductility ensures plastic deformation and a tight seal.

I made tons of bored thread 2 IPS pipe fittings when I was an apprentice and I caught hell if I took over 7 cuts start to finish.

When you get into the rhythm og thread cutting you can go like hell at 600 RPM and more with a carbide tool. Well, maybe (I can't now, but I could when my eyes were sharp and reflexes like lightening before dinosaurs.

[This message has been edited by Forrest Addy (edited 04-21-2003).]