How to call out a NPT Thread

[LONDONDERRY]

How do you call out a NPT thread length on a drawing?

I have a part that is 17.75 mm thick and I called out a 1-11.5 internal NPT pipe thread. The tap has a tapper on it, s if I don't tell where to the machinist to stop in depth with the tap, the hole will be over sized, so the NTP fitting will not thread in tight. Do you understand?
So how do I call out on a drawing, how much of the tep in length to us?

Frank

 

[MechNorth]

Unfortunately, I have had to specify depth on occasion. Typically it dealt with thin wall-sections and the risk of stress-concentration-factors when the tap got too near to the wall as the result of an excessively deep tap. There was a range of experience levels among the machinists doing the work and, again unfortunately, when you're dealing with volume & timing it's easy to overdo a tap depth. I would have liked to use a Lee Plug in those instances, but that was too radical for management.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[aardvarkdw]

If the depth is critical to function, in a section view dimension the depth of the thread in profile. This is the least ambiguous way to show depth.

David

 

[dimjim]

What goes into the threaded hole?
Most fittings stick out sufficiently
that it is very hard to over tap the
holes. Just curious why you are calling
out such a large pipe tap. Won't a
smaller pipe plug allow just as much
grease to be supplied per hole?