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NPT threading

cimber

Plastic
Joined
Nov 15, 2015
I am trying to figure out this npt chart in the machinist handbook. All I want is the start and stop points for a 3/4 npt. I want to bore it to size then put a chamfer on it. If anyone can tell me what size to bore it to and how deep would be great. Pictures would make it even better. Thanks!
 
I am trying to figure out this npt chart in the machinist handbook. All I want is the start and stop points for a 3/4 npt. I want to bore it to size then put a chamfer on it. If anyone can tell me what size to bore it to and how deep would be great. Pictures would make it even better. Thanks!

Like that other thread without the chart says... Get some ThreadPal..

.935" at the pipe face. Taper in from there. And a thread depth of .0539"...

External is generally around 12 threads long, varies a bit, so somewhere around that
length..

Those #'s will give you a good starting spot... You always have to play with the
thread depth depending on your insert and how you set it.

Pipe threads are a bitch, and the Machinery's Handbook doesn't make it any easier.
There is always some trial and error, at least there is/was every time I've done
the damn things... Thankfully, its always been a "just needs to work" thing.
 
For many years I drilled to minimum diameter and then taper tapped to fit. I decided to use dedicated pipe tapered reamers. They work much better. I still tap to fit, but the ease of tapping and the thread quality is much better. These reamers are well worth their cost.
 
Whenever you say " pipe face " is that considered Z 0. or is that after you chamfer the hole?
 
Whenever you say " pipe face " is that considered Z 0. or is that after you chamfer the hole?

I've always considered it where the taper intersects the pipe face(Z0)... When you chamfer it, that dimension
just kind of disappears, or at least is gets really hard to measure since its sitting out in the middle of
nothing.
 








 
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