cutting (US) pipe taper thread

Well really, it looks like it is easiest & fastest to just order a T-fitting and nipples already made off of McMaster,,, but I am still curious.

The methods that I have seen for cutting tapers (or tapered threads) on a normal lathe is to offset the tailstock, and spin the part between centers... but you can't do that if you're cutting internal threads.

So that is why I am wondering how to cut internal tapered threads on a manual lathe without a taper attachment, or if it can even be done.

You can get taps.

Where are you, Beverly Hills?

Around here every surviving (= well-run) small hardware store carries or can get them:

I found grinding flutes in a steel plug was good enough for chasing crud out of brass threads for replacing a showerhead arm. It meant I didn't have to rip open the wall, but I don't know how well it would have cut new threads in aluminum. I've found pipe taps at local secondhand tool stores but the ones I had on hand bottomed out before the threads engaged, so I improvised.

If all he needs is fittings (tees and pipe nipples) I guess I'm confused on why he needs to make them rather than buy them in brass, I can find 3/8 sizes even at the big box stores, they might just be across the aisle from the large fittings in little bags/bins. Got to be cheaper than a tap.

--Glenn Lyford

Both are tapered, at least the ones I have on hand are. Make sure what you have, there's a straight series as well. A Real Hardware store should have pipe taps at least up to 1/2", a big box home improvement joint, probably not. I've seen button dies for small pipe sizes, The larger ones tend to have separate chasers, just because of the thread length. The local hardwares have all sorts of hose barbs in whatever pipe sizes needed, in brass and for a price, but they ARE available. If you're in the boonies, you may have a time locating parts. NAPA has some hose fittings as well, you just have to decide what exactly you need.

Stan

"Stanley Schaefer" wrote

Outside of hydraulics I've seen straight pipe-sized threads only on screw-in water heater elements and shower head adapters.

jsw

Yes, of course the usual pipe taps are tapered. You will want to use Al parts, because Cu is a major corrosion issue -- maybe galvanized is OK, though.

If you bore and straight-thread on the lathe, the final machining is just a quick touchup with the tap. Just look for NPT taps, stands for National Pipe Thread.

Just to be clear, pipe thread 1/8 is suitable for pipe of 1/8" internal diameter, about 3/8" external size.

whit3rd wrote: ... Just look for NPT taps, stands for

Actually, it stands for National Pipe Tapered. And NPS for National Pipe Straight.

Bob

Well I did end up just ordering some aluminum nipples and a "T" fitting from McMaster. 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.

Electrical conduit & fittings and lamp parts are NPS.

lathe that didn't have a taper attachment.

Basically, you don't

that didn't have a taper attachment.

Well, you can set the tailstock over to cut *external* threads on an emergency pipe tap. But it won't work if the workpiece is too long. You're limited by how far you can set your tailstock over.

that didn't have a taper attachment.

Wait a minute. If you're cutting internal tapered threads, you can set that up with the compound and use the compound feed. Right?

Yes, you can't.

And doing an external tapered thread without a taper attachment can also be tricky, depending on the length of the pipe to receive the tapered thread. If it is too long, you can't mount it between centers. And you may not be able to get enough offset in the tailstock to get the right taper, either. (BTW, turning between balls might be easier than between centers for pipe. Make up centers which end in hardened balls.

Yes -- with a tap made for the thread in question. They are made and sold. I have some of various (small) sizes.

There are also matching dies.

And there are chasers for Geometric die heads to cut tapered threads as well as straight ones, if you happen to have a bed turret for the lathe.

Enjoy, DoN.

Depends on what type of crashbox you have.

Best Regards Tom.

A turret may be convenient, but I mount the Geometric head in a boring bar holder on the toolpost.

Conduit uses a tapered male thread; female threads on conduit fittings are generally NPS.

I'm fairly sure I've seen both straight and tapered, depending on if it was indoor or liquid-tight, cast metal or plastic box. The plastic imitation Sealtite that Lowe's sells uses straight male threads and an O ring. I don't have other samples handy to check.

I should have qualified my statement with "plumbing" though he's not likely to use an electrical conduit fitting on the radiator.

jsw