Re: [mill_drill] odd way to describe threads
- Hi,I recall working on a 316L stainless steel bioreactor where the threaded port was 11 TPI - the NPT used 1 1/2 TPI and the probe would not fit. The port is referred to as a 25mm port (ID size). As the system was steam sterilized steam and needed to have high containment (bacteria are small), a good fit was important.Off to a local plumbing shop to rent a die, wrench and cutting oil to re-thread six ports. The 1/2 TPI difference wasn't structural and it was common practice to run both threads so that the clients could use either the NPT or BSP probes.Be well,DBN
--- On Mon, 5/6/13, Jerry Durand <jdurand@...> wrote:
From: Jerry Durand <jdurand@...>
Subject: Re: [mill_drill] odd way to describe threads
Date: Monday, May 6, 2013, 2:19 AMOn 05/05/2013 10:55 PM, Craig E. Johnston wrote:
Re the pipe threads: some metric pipe threads are very close to NPT sizes – the coolant nipple on my RF-45 clone table was slightly different diameter than 3/8” NPT, but the threads were almost the same. Since the nipple was in the way of the x-axis glass scale, I turned a (metric threaded) plug to close it off and drilled and tapped a ¼ NPT hole in a better location.
I have also had the experience of buying plumbing fittings in New Zealand to work with American NPT fittings on my boat, and found that they were almost the same. Up to about ½” I could mate them, but larger sizes simply didn’t go together.
A wise old friend, who at the time was building his own 38’ sailboat, once commented that “plumbing really sucks…”
My wife used to work in a steel shop (designer and fabricator). They once got in a shipment of steel from the EU and it was ALMOST the right inch size. It was off just enough that it would jamb the shear in the hydraulic iron worker. So that entire load had to be cut on the band saw.
-- Jerry Durand, Durand Interstellar, Inc. www.interstellar.com tel: +1 408 356-3886, USA toll free: 1 866 356-3886 Skype: jerrydurand
- If it's close, a little thread chasing should get you enough engagement.
After all, the purpose of pipe threads is to jam.
This makes it a lot easier than if they were to fit over several
diameters length. With the crazy specifications used in plumbing, it's
amazing how well parts interchange and fit.
Jerry Durand wrote:
> I ordered one of the Chinese valves, I'll try to remember to post a note
> if it really is 3/8 NPT when it gets here. Otherwise I'll be making an
> adapter. :)
> Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
> tel: +1 408 356-3886, USA toll free: 1 866 356-3886
> Skype: jerrydurand