I'm just too lazy to look it up, but if you have almost any smaller diameter
tap with the same thread pitch, it can be used to cut a tapered thread.

The tap is mounted in the toolpost with the cuting edges properly oriented,
then bump the toolpost so the tap's free end moves inward slightly.

A few trial/error attempts on scrap practice pieces should get the tap
angled just enough to match the pipe thread taper.

I'd suggest a hand crank on the spindle After pulling the lathe's power cord
plug from the receptacle, and using a generous amount of quality cutting
lubricant.

Set the feed rate to match the thread pitch, and use the off-axis tap as a
multi-point boring bar.. feed in with the hand crank for a light cut, back
the cross feed in, back up the carriage, adjust for another light cut,
engage and turn crank.. repeat until diameter and depth (thread count) are
achieved.

It's not as easy to get answers to some types of metalworking questions when
so many talented and bright metalworkers have stopped participating in RCM
as a result of disgust over the rampant, senseless off topic bull****.

Yep, RCM is where I learned such tricks, years ago.

--
WB
..........


"DougC" wrote in message
...

The remaining question was how to cut internal tapered threads on a lathe
that didn't have a taper attachment.

I saw the NPT taps at Enco, $28 for a 3/8"... Enco was offline at that
moment...

I noticed that the temperature sensor was brass, and it screwed into an
aluminum thermostat housing--and there appears to be some brown corrosion
in the aluminum thermostat housing threads. I couldn't tell from briefly
looking if that was the aluminum corroding or not. I had not seen this
connection leak before, so the rust I saw may have been free-floating rust
from the iron engine block (this is why I built the magnetic trap in the
new radiator tanks).


I know that the local hardware store sells brass and steel/zinc plumbing
fixtures, but I wanted at least one aluminum nipple to screw into the
remaining thermostat housing threads. ...As for the remaining components,
I got them in aluminum also since I had to mail-order the one aluminum
nipple from McMaster, and the thermostat sensor can be grounded directly
off its own body so there will be no current flowing through the
brass/aluminum there connection at all. This may not eliminate corrosion
in the sensor threads, but should drastically eliminate it.