Wierd pipe size

[toprecyler]

I work in a hydraulic rebuilding shop. I ran across an odd pipe size today. It is on an internal port tube, inside the chrome OD rod of a cylinder. This is because both ports to this cylinder are connected thru the rod end mounting.

The piston end of the port tube is sealed in the end of the rod with two o-rings. Somewhat typical.

The other end is threaded into the rod end mounting. With tapered threads. The OD of the port tube is .750”. Here is the wierd part, the threads are 16 TPI.

Ok, so maybe not so wierd, since the tube is in between 3/8” pipe and 1/2” pipe size. Pipe threads are usually 18 TPI.

So my co-machinist asked me to do these threads for him. He has never used the taper attachment on his lathe, and I have several times. This will be the first time making tapered threads though.

I’m guessing the OEM manufacturer had special tooling made up to make this originally.

We would have liked to reuse the old port tube , but it took on the z shape of the bent rod.






Sent from my iPhone using Tapatalk

 

[Ischgl99]

The thread you show is not 16 tpi, the teeth on the gauge don’t line up completely. Do you have a metric pitch gauge to check? If the 18 tpi gauge didn’t fit, I suspect it is 1.5mm. Do you know what country the equipment came from? There is a metric tapered pipe thread that uses a 1.5mm pitch. This thread standard only tapers the OD thread, the ID is straight. I worked for German companies a large part of my career, BSPP and BSPT were most common in fluid applications, but occasionally the older designs used some of the older standards.

Metric external taper thread DIN 158

 

[Jake M]

It's -07 pipe thread, where have you been?

I've seen that before. Not every day obviously. Check it and don't take my experience for gospel, but odds are (in my experience) it'll not be random, but if you work it back it's what a 7/16 pipe thread "would have been" if there was such a thing. One in sixteen taper, same thread form and angles, etc.

 

[toprecyler]

The thread you show is not 16 tpi, the teeth on the gauge don’t line up completely. Do you have a metric pitch gauge to check? If the 18 tpi gauge didn’t fit, I suspect it is 1.5mm. Do you know what country the equipment came from? There is a metric tapered pipe thread that uses a 1.5mm pitch. This thread standard only tapers the OD thread, the ID is straight. I worked for German companies a large part of my career, BSPP and BSPT were most common in fluid applications, but occasionally the older designs used some of the older standards.

Metric external taper thread DIN 158

Thanks for the info. When coworker brought it to me, first thing I checked was metric pitch. It was off a bit for that. 16 TPI was the closest.

After sleeping on it, and rereading your helpful site, I believe that they used a standard 3/4” 16 straight tap for the female hole, and threaded the pipe on a taper, like they said Din 158 uses.

But I will double check this morning when I get back to work. The female thread is difficult to see, because it is recessed about 4” down in the rod end mount.

I will try to get more pictures to explain better.


Sent from my iPhone using Tapatalk

 

[Ischgl99]

After sleeping on it, and rereading your helpful site, I believe that they used a standard 3/4” 16 straight tap for the female hole, and threaded the pipe on a taper, like they said Din 158 uses.

That could explain why the threads are not lining up with the gauge, they might have deformed them enough that none of the gauges will fit properly. I have seen plenty of times where someone used what they had instead of doing it right, so it’s hard to say what the OEM intended for that connection. If you are able to get a test piece into the internal threads, that might help decide which way to go.

 

[Eddyde]

It's -07 pipe thread, where have you been?

I've seen that before. Not every day obviously. Check it and don't take my experience for gospel, but odds are (in my experience) it'll not be random, but if you work it back it's what a 7/16 pipe thread "would have been" if there was such a thing. One in sixteen taper, same thread form and angles, etc.

I had never heard of this pipe threads so I looked it up.

ISO 7 - Pipe Threads where Pressure-tight Joints are made on the Threads

Pressure-tight joints made on the pipe threads.

www.engineeringtoolbox.com

Interesting, but it looks like none of the sizes are close to 16 TPI

 

[toprecyler]

So I managed to get the port tube taper threaded to 16TPI.

Did one sample piece, then did real thing. I had left the port tube full length piece, so in case I buggered the threads up, I could cut off and try again. Will cut port tube to finish length after threaded into the rod mount.

However, while threading I notice something weird with a taper attachment when the tool started threading the compound pushed back about .020” and made a straight thread for a bit before the taper started again. Due to the backlash in taper attachment. But if I was threading away from the Chuck, the taper would stay moving even if I turn the compound in more.

So I set up a sample piece to thread away from the Chuck. Figured it would be best to try one more now while fresh in my mind. It worked better this way. So then I redid the actual port tube thread.

So I spent roughly 4 hours doing one thread. . But it was a good learning experience. Another feather in my cap.










Sent from my iPhone using Tapatalk

 

[Jake M]

I had never heard of this pipe threads so I looked it up.

ISO 7 - Pipe Threads where Pressure-tight Joints are made on the Threads

Pressure-tight joints made on the pipe threads.

www.engineeringtoolbox.com

Interesting, but it looks like none of the sizes are close to 16 TPI

Upon reading that, it doesn't seem as "clearly sarcastic" as it did at the time. I was just poking fun at a thread that doesn't exist. All I was trying to say is that when somebody is in a corner (as can happen when making cylinders such as this), they might invent their own thread, but only the part that needs reinvented. If you take their OD, and thread pitch of the "custom" size, the rest of the NPT thread standard will still fit. The taper, the sharp V thread form, etc.

Sorry that really didn't come across how I intended it to.

 

[toprecyler]

Forgot to update this thread. Co-machinist ended up making the cylinder rod. I just made the port tube. So he put it together.

He was supposed to use red locktite and tighten it really tight. As far as I know, it is back in service with no problems. It passed our test stand, and I have not seen it back, so everything must be working again.


Sent from my iPhone using Tapatalk

 

[verbotenwhisky]

I work in a hydraulic rebuilding shop. I ran across an odd pipe size today. It is on an internal port tube, inside the chrome OD rod of a cylinder. This is because both ports to this cylinder are connected thru the rod end mounting.

The piston end of the port tube is sealed in the end of the rod with two o-rings. Somewhat typical.

The other end is threaded into the rod end mounting. With tapered threads. The OD of the port tube is .750”. Here is the wierd part, the threads are 16 TPI.

Ok, so maybe not so wierd, since the tube is in between 3/8” pipe and 1/2” pipe size. Pipe threads are usually 18 TPI.

So my co-machinist asked me to do these threads for him. He has never used the taper attachment on his lathe, and I have several times. This will be the first time making tapered threads though.

I’m guessing the OEM manufacturer had special tooling made up to make this originally.

We would have liked to reuse the old port tube , but it took on the z shape of the bent rod.


View attachment 465686
View attachment 465687


Sent from my iPhone using Tapatalk

That is a National Pipe Thread or NPT, tapered at 1/16" per inch. 1/2" ANSI pipe is actually .840" OD.