tapping tapered pipe thread

if i were to tap a tapered pipe thread into cast iron, is there some kind of
tapered reamer i'm supposed to use or is it ok to just drill a hole (with
parallel sides) and the tap automatically cuts the taper? i'm thinking
about 3/8" and 1/2" pipe.
Reply to
William Wixon
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The holes (typically) are drilled straight, and the tap does the taper. That's not the fastest or physically easiest way to cut a pipe taper (it turns pretty hard as the taper enters further and further), but it works just fine, so long as you lubricate the tap properly, and clear the chips frequently.
You will grunt some turning a 1/2" pipe tap by hand.
LLoyd
Reply to
Lloyd E. Sponenburgh
You can drill a straight hole.
Reply to
Ignoramus7272
It's really a lot less work if you do bore the hole with approximately the correct taper. Also, your taps will last longer. I have done this, and as I recall tapping for pipe thread isn't always trivial.
GWE
Reply to
Grant Erwin
You an do it with a drilled hole, but there are tapered reamers available to make the task a lot easier. Tom
Reply to
Tom Wait
thanks everyone! dang! i just realized i should've also included with my original question if anyone knows what size drill bit i should use to cut the 3/8" thread! (of if you know of an on-line chart to look up what drill to use!)
b.w.
Reply to
William Wixon
Just memory, which may fail, but I think 37/64 for 3/8, and 9/16 will work with some grunt??
LLoyd
Reply to
Lloyd E. Sponenburgh
Hint, for questions like this (tap/drill size), you can just see McMaster catalog online.
See McMaster item 2662A28 as an example.
You need to drill a 9/16" hole, as the spec says.
System of Measurement Inch Pipe Size 3/8"-18 Drill Size 9/16" Thread Type NPT (National Pipe Taper) Thread Direction Right-Hand Thread Tap Type Pipe Taps Pipe Tap Type Standard Tap Material Cobalt Steel Surface Coating/Treatment Uncoated (Bright Finish) Thread Length 1-1/16" Overall Length 2-9/16" Number of Flutes 4 Projection Length .454"
9/16 drill bits are common.
i
Reply to
Ignoramus7272
thanks again! (i was just going to make a further addition to my original post saying this is for a non-critical application, no pressure, not for a nuclear reactor facility, etc., but that's moot now)
thanks very much! (off to the plumbing supply store!)
couldn't think of where to look for the info. couldn't think of a way to phrase it to look in google (without having to sift through 57,000 hits)
b.w.
Reply to
William Wixon
By the way, pipe taps are not very expensive to buy used on ebay. I hope that you are not buying a pipe tap at the plumbing supply.
i
Reply to
Ignoramus7272
As others have said, you can drill a straight hole. I do some taper pin hole drilling/reaming. For that, I use a table of drill sizes that is to be found in Machinery's Handbook. The point is that you can drill all the way through with the minimum size drill bit, then drill part way through with a larger drill bit, removing a bunch of material so you don't have so much work to do with the tap. For my #7 taper pins (which are a lot smaller than your water pipe) I could even use 3 drill bits to do the job, but two make pretty easy work for the reamer.
Pete Stanaitis ----------------
William Wix> if i were to tap a tapered pipe thread into cast iron, is there some kind of
Reply to
spaco

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