Reusing threaded pipe

[Nevets01]

Not sure how many people have tried this...but anyway....a plumbing project I was working on called for just an inch or so of threaded pipe so I figured I'd cut it off the end of a scrap piece of pipe I had lying around after cutting off the amount of thread pipe I needed I cleaned it up filed it got all the burrs off and then tried threading it on to a fitting and it just won't thread on...I noticed some errors I made and tried again and after three times of cleaning and filing burrs it still would not thread into a fitting...I know they make 1inch threaded pipe but I figured what the hell I'll just make my own and this project isn't when finished anything to worry about like leaks of any kind or end up hazardous if something went wrong.....why wont threaded pipe rethread after cutting?..note: i do know some threaded pipe is flared or tapered at the end and chose a piece of threaded pipe that wasn't ....if anyone thinks they are wasting there time with me then by all means DON'T....3 attempts I've made with no luck anybody try doing this?...or know the answer as to why cut threaded pipe won't rethread?

 

[Reach4]

Your pipe die may be wrong. Is that die marked as NTP? Are you running the pipe through the die to where the open end is completely out of the die?

Are you saying that the pre-cut end of the pipe goes into your fitting, but the newly-cut end does not?

 

[Sponsor]

 

[hj]

Your description is somewhat confusing. Are you trying to connect fittings to BOTH ends of the cut off piece, or just the end of the pipe that was threaded? If you are saying that the threaded end doesn't fit, then you have damaged the thread. If you are trying to use BOTH ends of the piece, it will NEVER work.

 

[Jadnashua]

This type of threaded pipe is tapered, as opposed to a straight thread like on a bolt. So, the end that goes into the fitting will have a smaller OD than the top of the threads.

If you need two things connected by a short nipple, they sell what is called a close nipple...essentially, it's a short piece of pipe with the correct threads on both ends, i.e., the outer ends are smaller. WHen tightening up this type of threaded fitting, you're literally wedging the nipple into the fitting. To fill the gaps, you need either some tape or pipe dope, or, even though it may be tight, there will be a path through the threads for it to leak.

 

[Nevets01]

Your description is somewhat confusing. Are you trying to connect fittings to BOTH ends of the cut off piece, or just the end of the pipe that was threaded? If you are saying that the threaded end doesn't fit, then you have damaged the thread. If you are trying to use BOTH ends of the piece, it will NEVER work.

Ok yes.....I was trying to use both ends of the piece...and why wouldn't it work? the threads seemingly go in the same direction of rotation....I mean I know it doesn't work I tried 3 times each time with a different threaded end piece....can you explain why it will never work?...really would be appreciated....thnx....

This type of threaded pipe is tapered, as opposed to a straight thread like on a bolt. So, the end that goes into the fitting will have a smaller OD than the top of the threads.

If you need two things connected by a short nipple, they sell what is called a close nipple...essentially, it's a short piece of pipe with the correct threads on both ends, i.e., the outer ends are smaller. WHen tightening up this type of threaded fitting, you're literally wedging the nipple into the fitting. To fill the gaps, you need either some tape or pipe dope, or, even though it may be tight, there will be a path through the threads for it to leak.

This type of threaded pipe is tapered, as opposed to a straight thread like on a bolt. So, the end that goes into the fitting will have a smaller OD than the top of the threads.

If you need two things connected by a short nipple, they sell what is called a close nipple...essentially, it's a short piece of pipe with the correct threads on both ends, i.e., the outer ends are smaller. WHen tightening up this type of threaded fitting, you're literally wedging the nipple into the fitting. To fill the gaps, you need either some tape or pipe dope, or, even though it may be tight, there will be a path through the threads for it to leak.

Thnx...yes I do know they sell this part..I wanted to make one myself and thinking nothing of it...I tried and to my disappointment I couldn't make one...

 

[Nevets01]

Your pipe die may be wrong. Is that die marked as NTP? Are you running the pipe through the die to where the open end is completely out of the die?

Are you saying that the pre-cut end of the pipe goes into your fitting, but the newly-cut end does not?

Ok...I didn't use a die...I just simply cut it off with a hacksaw...and yes the newly cut end does not thread as it seems like it should as the direction of rotation is the same...what am missing here or not getting...perplexed...

 

[Nevets01]

I think I just figured it out...on the newly cut end the spiral even though its still going clockwise the pitch or whatever is going in the opposite direction in other words the newly cut end looks to be spiraling down when it should b spiraling up...well thanks guys y'all made me take another look at this and now it all makes sense....

 

[hj]

It does NOT ""Make sense". It will never work because the threads taper from the end of the thread and get "wider" as they approach the "pipe" end of the thread. So it enables the joint to become tight and not leak. You are trying to screw a fitting on to the widest part of the thread, which is where a fitting should never be able to reach without major over tightening and stretching the female portion.

 

[Nevets01]

Dude...did u read my initial thread...I was using threaded pipe that wasn't flared nor tapered....nevertheless i figured out and realized that its impossible...when trying to thread into a fitting with the newly cut end I found even though its a clockwise rotation the pitch of the threads are reversed making it impossible....there is an upward rotation and a downward rotation the cut end is a downward rotation trying to thread into an upward rotation of the fitting rendering it impossible so it could NOT start on the flared end anyway...it just won't let you...I feel a little bit on the air head side now but glad I figured it out thanx to y'all I took a second look at it..was ahaa moment.. and had to laugh at myself....it's all good my friend...thnx...

 

[hj]

quote; when trying to thread into a fitting with the newly cut end I found even though its a clockwise rotation the pitch of the threads are reversed making it impossible....there is an upward rotation and a downward rotation the cut end is a downward rotation trying to thread into an upward rotation of the fitting rendering it impossible so it could NOT start on the flared end anyway

I have NO IDEA what that all means, but it is "nonsense". The cutoff thread DID have a taper, and if the OTHER END had a taper also it would have worked, but YOU do not have the equipment to create that taper. And before you reply that I do not know what I am talking about, I will place my 65 years experience against whatever you have as a plumber.

 

[Jadnashua]

WHen you cut NPT threads, one side of the die has a bigger opening than the other. IOW, as you cut the threads, it's cutting more and more off of the outer edge of the pipe than on the inner end of the threaded portion...it creates a tapered end on the pipe. It isn't a huge taper, but it's there. You cannot try to start the thread with putting the die's smaller opening on the end of the pipe...it just won't go, which is the same as what you're trying to do by just cutting off a threaded section of pipe. If you look at it carefully, it should become obvious that the threads are deeper towards the end than they are further up.

As I said earlier, NPT threads are NOT like a bolt where you can run a nut up/down it anywhere and it doesn't tighten up...the NPT threads are tapered, so as you screw it into a fitting, it acts like a wedge and tightens up.

So, if you need a short (close) nipple, the threading operation needs to be started from both ends so that each end is tapered and it will tighten up. If you were to just run the die all the way through the pipe's length, it would cut the threads evenly, and it would never tighten up and likely leak, but you'd be able to screw things on. The pipe would likely bottom out in a fitting without being tight or secure.

 

[Nevets01]

It does NOT ""Make sense". It will never work because the threads taper from the end of the thread and get "wider" as they approach the "pipe" end of the thread. So it enables the joint to become tight and not leak. You are trying to screw a fitting on to the widest part of the thread, which is where a fitting should never be able to reach without major over tightening and stretching the female portion.

quote; when trying to thread into a fitting with the newly cut end I found even though its a clockwise rotation the pitch of the threads are reversed making it impossible....there is an upward rotation and a downward rotation the cut end is a downward rotation trying to thread into an upward rotation of the fitting rendering it impossible so it could NOT start on the flared end anyway

I have NO IDEA what that all means, but it is "nonsense". The cutoff thread DID have a taper, and if the OTHER END had a taper also it would have worked, but YOU do not have the equipment to create that taper. And before you reply that I do not know what I am talking about, I will place my 65 years experience against whatever you have as a plumber.

Ok please if you have no idea just take the newly cut end and put it side by side with a factory end meaning not cut and look closely u will see the factory end has a clockwise direction going up and the newly cut end has a clockwise direction going down...so it is impossible...look very closely at the threads...now if you have a tool that can change that fine because u will need it otherwise it won't work!! and let me quote you...you said you have no idea what all that means...if you have 65 years or 65 hours it doesn't matter...it won't work...maybe you will have to bench test this or again look closely at the threads when they are side by side..the newly cut..put that end up and the factory end...put that end up...now put them side by side...threads are going in opposite directions but both still going clockwise...NOT GOING TO THREAD into a fitting....just look or even try it!!!

 

[Jadnashua]

The outer, threaded end is smaller in OD than the pipe further up the pipe. It's not a huge amount, but it is there. That's so it can thread into the fitting and tighten down as it is threaded in. It is TAPERED, again, it is NOT like a bolt that has straight, even, threads all along its length. You can't put the wide end of a wedge in and expect it to do much...you put the narrow end in first...you need to do that with an iron pipe threaded connection, too. YOu might need a micrometer to tell, but it is there.

NPT thread is tapered at 1" in 16", so it's not a steep taper, but it's there. A typical threaded connection isn't inserted far before it tightens up, so the difference in the end verses where it tightens isn't all that far so the difference isn't that much.

 

[Reach4]

Ok please if you have no idea just take the newly cut end and put it side by side with a factory end meaning not cut and look closely u will see the factory end has a clockwise direction going up and the newly cut end has a clockwise direction going down...so it is impossible...look very closely at the threads...now if you have a tool that can change that fine because u will need it otherwise it won't work!! and let me quote you...you said you have no idea what all that means...if you have 65 years or 65 hours it doesn't matter...it won't work...maybe you will have to bench test this or again look closely at the threads when they are side by side..the newly cut..put that end up and the factory end...put that end up...now put them side by side...threads are going in opposite directions but both still going clockwise...NOT GOING TO THREAD into a fitting....just look or even try it!!!

While there are pipes with clockwise threads on one end and counterclockwise threads on the other. However they are special purpose. You probably don't have one of those.

 

[Cool Blue Harley]

Priceless.

 

[Jadnashua]

Priceless!

You can’t cut the end of a threaded pipe to create your own close nipple, taper or no taper.

The threads on a nipple oppose each other.

You need a special chuck to hold it, but the same die is used to make the threads on both ends. While something like a turnbuckle will have a left and right hand thread on opposite ends, a nipple has exactly the same threads, but you can't just start at one end and run to the other then cut the pipe off...you have to turn the thing around and start on the other end once you thread it half-way in the case of a close nipple, or as far as normal for a longer length one. The threads are identical on each end, but taper towards the middle getting larger in diameter.

Not sure what the confusion here is...to insert a pipe nipple into a fitting...you must insert the smaller end, not the larger end since it plain just doesn't fit and won't wedge itself tight even if you could get it started.

 

[Cool Blue Harley]

You are correct.
The tapers oppose each other.

 

[hj]

Francis Bacon wrote, "A man convicted against his will is unconvicted still" so you can just go on believing what you wrote, whatever it means, because it is nonsense.