NTP Thread Milling

[SnowDay]

I am getting ready to start thread milling 1/4 - 1 NPT threads but have a few questions. Mastercam wants to know the the major dia of the ID threads but the Machinery Handbook gives me pitch dia of the beginning of the ext thread. So say for a 1/4-18 pitch NPT thread the dia in .47739 at a depth of .2278 at least thats what I think it is telling me. I want to run my thread mill down -.62 the thread mill dia on the tip is .331 How do I know what to enter for the major dia in Mastercam ?

 

Thanks

[[email protected]]

I use points for geometry and the chart I have states:

Internal 1/4-18 NPT .594 Depth

.540 major dia. but when I went by this chart .540 is too big and it ended up being .513 for my threadmill

 

You will also have to put 1.789 in the taper angle

 

HTH

 

Edit: My threadmill is .331 also

[[email protected]]

I found this chart somewhere on the 'net but I cant find it again. I had this copied and pasted into ms word.

 

Like I stated above, use points for geometry and it shows another field for "Diameter" and for your first try I would type in about .030 or .040 less than the chart diameter and "Sneak up" on it until you achieve proper diameter and then document it in your word file (Like I haven't done yet!!)

 

INTERNAL NPT PIPE THREAD ENGAGEMENT DEPTH CHART

 

1/16 - 27 TPI NPT = .389

1/8 - 27 TPI NPT = .392

1/4 - 18 TPI NPT = .594

3/8 - 18 TPI NPT = .600

1/2 - 14 TPI NPT = .781

3/4 - 14 TPI NPT = .793

1 - 11 1/2 TPI NPT = .984

1 1/4 - 11 1/2 TPI NPT = 1.008

1 1/2 - 11 1/2 TPI NPT = 1.025

2 - 11 1/2 TPI NPT = 1.058

2 - 8 TPI NPT = 1.571

3 - 8 TPI NPT = 1.633

 

USE ENGAGEMENT DEPTH TO CALCULATE BOTTOM OF THREAD IN 'Z' AXIS

 

INTERNAL NPT PIPE THREAD MAJOR DIAMETER CHART

 

1/16 - 27 TPI NPT = .312

1/8 - 27 TPI NPT = .405

1/4 - 18 TPI NPT = .540

3/8 - 18 TPI NPT = .675

1/2 - 14 TPI NPT = .840

3/4 - 14 TPI NPT = 1.050

1 - 11 1/2 TPI NPT = 1.315

1 1/4 - 11 1/2 TPI NPT = 1.660

1 1/2 - 11 1/2 TPI NPT = 1.900

2 - 11 1/2 TPI NPT = 2.375

2 - 8 TPI NPT = 2.875

3 - 8 TPI NPT = 3.500

 

HTH

[SnowDay]

Thank You

[[email protected]]

You're welcome