O/T NPT Thread Milling

[Peccator]

I,m trying to thread mill an NPT 1-1/4 11.5 T.P.I.

It is an internal thread. I know that my minor hole diameter should be 1.485.

 

What I,m looking for is the major diameter to program my thread mill to. Can y'all help me out,please?

 

I'm having a hard time trying to understand my Machinery's Handbook.

[Toolfab]

1.468 is the reamed hole dim. I dont know about major but you could start there and then cutter comp it out till you get what you want.

[Peccator]

You are right there Toolfab. But, I,m looking to try and program it all at once with multiple passes for rough and finish. And it would be helpful to know the major diameter to program right the first time, given the actual cutter diameter.

[Nominal]

You must have a gage to check this with after you start cutting. I'd use that as a reference. But anyways the height of the thread is about .069. You of course realize that this is tapered 1 deg 47 minutes so the minor dia of 1.4876 only applies to the small end at the length of engagement.

[Peccator]

Yes, we do have the mating part to to this. And, yes, I understnd about the taper.

 

 

BTW.?

 

Is it easier to run an NPT thread insert or to single point thread mill?

 

We are running this on a Mazak and using a single point mill and stepping out .01 each time til we achieve required fit.

Comp control is set to control.

[Toolfab]

I would think it would be easier to use a multiple flute solid carbide threadmill and interpolate the hole in one 360° motion.

 

 

But thats just me...lol

[Carl Vallance]

Rookie 1,

Specs from ThreadTech program:

OSBORN PRODUCTS INC.

.............DATA FOR PIPE THREADS.............

 

................. 1 1/4-11.5 NPT ..............

 

Outside diameter of pipe....................... 1.6600

Threads per inch............................... 11.5

Decimal lead................................... 0.08696

P.D. at beginning of external thread (E0)...... 1.55713

Length of handtight engagement (L1)............ 0.4200

Number of threads engaged...................... 4.83

P.D. at length of handtight engagement and at

gaging notch or large end of internal thread(E1) 1.58338

Effective thread length of external thread (L2) 0.7068

Number of threads in effective thread length... 8.13

P.D. at effective thread length, external (E2). 1.60130

Length from handtight engagement to effective

thread length.................................. 0.2868

Number of threads from handtight engagement to

effective thread length........................ 3.30

Wrench makeup length for internal thread (L3).. 0.2609

No. of threads in makeup length for int. thd... 3

P.D. at makeup length for internal thread (E3). 1.54083

Vanish thread length........................... 0.3017

No. of threads in vanish thread length......... 3.47

Overall length of external thread.............. 1.0085

Nominal complete external thread length (L5)... 0.5329

P.D. at nominal complete ext. thread length(E5) 1.59043

Height of thread............................... 0.06957

Increase in diameter per thread advance........ 0.00543

Width of flat is...................from 0.0033 to 0.0073

 

 

Hope this helps.

[Peccator]

Thank you Carl.