Need dimensions for cutting internal 2" pipe threads!

[mh454]

Hello all. I'm a student in machining and need your help. A friend of mine gave me a project that I'm capable of doing but just need some dimensions for some threads. Basically is a rotating assembly for some large hose (same as your normal garden hose reel but with 2" hose). The fitting that is used is a 2" NPT. The only pipe treads I made in class so far were done with a pipe reamer and pipe tap (3/4"). We had a dimesion on the blueprint that was the opening of the hole for reaming (basically kept reaming till I got that opening dimension). Well this project is a bit different since I will be boring the internal taper and cutting the threads. We need at least 1.5" of threads so I will be cutting a 1.5" long taper (which I belive is 3/4" per foot). Anyone know how I can figure out how big to bore for the threads? Sorry if this is kinda vague but I'm new to this stuff.

 

[matt_isserstedt]

Machinery's Handbook quotes two different tap drill sizes for internal dryseal taper pipe threads.

For 2" NPT x 11.5 tpi the Mach. H-book suggests a drill size of 2-3/16" when drilling alone (no reaming).

For use with a reamer it suggests a 2-11/64" pilot drill size.

I am copying all this from Table 8 in the pipe thread section (page 1780 in #25 edition).

-Matt

 

[E-Stop]

The tap data I use shows that the minor diameter of the hole should be 2.227 at the face of the part and then taper in at .0625 per inch (or 3/4" per foot, as you stated). But a typical 2-11 1/2 NPT thread doesn't need to be 1.5" deep. So you may need to adjust the minor diameter at the face of the part so the bottom of the hole is not too tight. Typical depth of threads is about 1.100 with an effective length of threads of .756 (8.7 threads).

(This information is from the THREAD DATA module of Michael Rainey's ME Consultant Software.)

 

[mh454]

E-Stop: So boring the hole to 2.227" at the very face is what I need before cutting threads correct? And yes 1.5" is probably not necessary for depth. Now that I look at the fitting, 1.1" deep would be sufficient. Thanks.

 

[E-Stop]

That is correct, if you are going to cut the bore with the 3/4" per foot taper. If the bored hole is straight then the nominal size is 2.190