Enlarging a 3/8npt thread.
Enlarging a 3/8npt thread.
(OP)
Hi all,
I have a question related to tapping.
I have an aluminum part that has two 3/8NPT threaded holes. They work fine with Earl's NPT to AN adapters. The only problem is that most of these adapters (including Russell's and XRP's) have higher profiles. I need adapters that can mate closer to the part surface.
I can think of two ways around this:
1. Tap the 3/8NPT threads deeper so that I can tighten the 3/8NPT adapters deeper as well.
2. Enlarge/re-tap the 3/8NPT threads to, say, M18x1.5 threads and use metric adapters, which will mate with the surface, thus lower height profile.
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Option 1 is not feasible unfortunately due to a limited bottoming issue with the 3/8NPT tap. Drilling the hole further is not an option unfortunately.
I am hoping for Option 2. My reasoning is based on this. 3/8NPT threads have a 1.5 pitch, much like the pitch in M18x1.5. Also since 3/8NPT OD ranges from 16.4mm to 17.5mm, I am guessing tapping for a M18x1.5 should work.
======
Does anyone has any prior experiences with this? Any advice,comments greatly appreciated.
Thank you for reading.
I have a question related to tapping.
I have an aluminum part that has two 3/8NPT threaded holes. They work fine with Earl's NPT to AN adapters. The only problem is that most of these adapters (including Russell's and XRP's) have higher profiles. I need adapters that can mate closer to the part surface.
I can think of two ways around this:
1. Tap the 3/8NPT threads deeper so that I can tighten the 3/8NPT adapters deeper as well.
2. Enlarge/re-tap the 3/8NPT threads to, say, M18x1.5 threads and use metric adapters, which will mate with the surface, thus lower height profile.
======
Option 1 is not feasible unfortunately due to a limited bottoming issue with the 3/8NPT tap. Drilling the hole further is not an option unfortunately.
I am hoping for Option 2. My reasoning is based on this. 3/8NPT threads have a 1.5 pitch, much like the pitch in M18x1.5. Also since 3/8NPT OD ranges from 16.4mm to 17.5mm, I am guessing tapping for a M18x1.5 should work.
======
Does anyone has any prior experiences with this? Any advice,comments greatly appreciated.
Thank you for reading.





RE: Enlarging a 3/8npt thread.
http://www.zeroleak.com/specs/ports.html
Ted
RE: Enlarging a 3/8npt thread.
Or I may have misunderstood the problem, again.
Mike Halloran
Pembroke Pines, FL, USA
RE: Enlarging a 3/8npt thread.
Software For Metalworking
http://closetolerancesoftware.com
RE: Enlarging a 3/8npt thread.
if you are the producer of the part, you can use your CNC mill to mill the threads.
Mike Halloran
Pembroke Pines, FL, USA
RE: Enlarging a 3/8npt thread.
@ mrainey : I think the short projection is the solution! I didn't know it's called just that. I kept doing a search on bottoming npt tap and google must have missed the link to short projection.
Thanks all for the replies. I will post with results once I have the short projection tap. :)
RE: Enlarging a 3/8npt thread.
The short projection tap came in (mcmaster 2553A14) and from first look, this SP tap looks just like a standard tap. I don't see the 'shortness' of it.
I tried the SP tap and it didn't go any further than the standard tap. :(
Here's a pic. Guess which one is the SP tap?
htt
RE: Enlarging a 3/8npt thread.
I found this from Greenfield taps.
http://www
Turns out McMaster carries only the short version and that was what I purchased. What I really needed is a extra short version.
RE: Enlarging a 3/8npt thread.
This means that, as it is a tapered thread, you will start cutting material before you hit the bottom of the hole.
Good luck and I hope that helps.
RE: Enlarging a 3/8npt thread.