NPT Threads

Often times we are putting an NPT thread into a flat bottom. In the case of an open bottom we run the threads out below the minor dia. However in the case of a blind hole its not possible. We are currently cutting a 1/4 NPT to a max depth of .350". How do you handle this? We take the taper 1.783 deg and work back from the tap drill size. It is a trial and error until we achieve the desaired result. Do you have a better way?

Lathe or mill?

I threadmill.

Try this:

regards

Process is in a lathe. Regardless of the machine, were do you get accurate numbers? Machineries Handbook does not give open ended numbers. I have been using CAD as a through hole and then just trim it from the back until I can get the numbers I want.

The numbers are derived from the machineries handbook.

regards

Gagemaker Software gives pretty accurate numbers....

www.gagemaker.com

I bought the thread disk software and have used it everyday since... Great investment.

Thanks for the info guys, but I think that everyone has missed the point. Or I have not asked correctly. I understand the thread, and I have the thread numbers from the book or cam1's chart (very handy). Gibbs wants them like this: (1/4 NPT, .350 dp in a blind bottom. ? signifies I am not sure)
Style: NPT
Nominal Xd: .540?
TPI: 18
Taper (slope): .0312
# of Starts: 1
Major Xd: .540?
MinorXd: .447? (from cam1's chart)
Thread Ht Xr: .0465 (auto calcs the diference)
Z start: .084 (I started in front of the part in order to get the length simplified)
Z End: -.310 (bore is .350, need clearance)
I want to speed up my process or the future. What numbers would you use and how would you go about getting them?
John

I talked to a Gibbs person about NPT threads and he e-mailed me all the NPT threads and I just put them in my Process file, and have cut pipe threads with that ever since then. If my Z-Axis changes I just change my end point like on a straight thread.

Daleb that sounds great. I can just vary me z depth. Will you share the files with me?

I would if I could. I've tried and I can only send as a TXT file and I don't that will work. Call your local salesman or if you have a tool show coming up in your area and talk to them. That is how I got the info.

I have to look around through my files. I think I have these on a disk someplace. I make backups to various formats and then forget where they are. If or when I locate them, how do you use them or install them?

I didn't have the NPT info with my Gibbs. That is why they sent it to me. Maybe it should have came with an update, but I did not get it.

You can download the NPT processes from gibbsonline if you are on maintenance. If anyone wants them, pm me a e-mail address and I'll send you a copy.