cutting (US) pipe taper thread

I don't doubt that some fittings, especially those for products other than rigid conduit, have straight male threads. But tapered threads are specified for the ends of conduit.

From Wheatland?s website:

Wheatland?s Galvanized steel Rigid Metal Conduit (RMC) is manufactured in accordance with the latest specifications and standards of ANSI ® C80.1, UL-6, and federal specification WW-C-581. The pitch of RMC threads conforms to the American National Standard for Pipe Threads, General Purpose (Inch), ANSI/ASME B1.20.1. The taper of threads is 3/4 inch per foot (1 in 16).

And the NEC specifies tapered threads for field threading:

344.28 Reaming and Threading. All cut ends shall be reamed or otherwise finished to remove rough edges. Where conduit is threaded in the field, a standard cutting die with a 1 in16 taper (3/4-in. taper per foot) shall be used. FPN: See ANSI/ASME B.1.20.1-1983, Standard for Pipe Threads, General Purpose (Inch).
Reply to
Ned Simmons
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Ed Huntress wrote: > Wait a minute. If you're cutting internal tapered threads, you can set

If you can crank the compound wheel at just the right speed to get the tpi you need. Give that guy a dope slap ... no, wait - it's Ed. Even he can goof up.

Bob

Reply to
Bob Engelhardt

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 bullshit.

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

Reply to
Wild_Bill

that didn't have

Do you have a compound feed geared to the spindle? You could turn a short internal smooth taper, but without the gearing, threading is sort of out of the question. :-) I've never seen one so equipped.

Enjoy, DoN.

Reply to
DoN. Nichols

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I've suggested that as a possibility in the past, but never tried it myself, since I *have* the bed turret. :-) Mostly, it requires some tricky centering to get it right.

Enjoy, DoN.

Reply to
DoN. Nichols

Both are tapered. At least for NPT.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Reply to
Wes

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