Chasing threads using a tap?

ranzerox

I have some rusted threads inside a coupling and I'm thinking of cleaning it out with a tap. Anyone try this? Thanks!

ratio

Might be cheaper to buy a new coupling, a big NPT tap will be expensive; but chasing threads (technical term) is a real thing.

retiredguy

Instead of a tap, which can enlarge the the socket point too much, you could try to clean the threads with a copper fitting brush. I normally carried them in sizes up through 2". I would cut off the handle and put them into a drill to hasten the job. You can sometimes find these brushes in larger sizes. I carried pipe taps from 1/8" through 2" and had a place near me that would rent 3" and 4" until I convinced the boss to buy the larger sizes.

Bob Vennerbeck

Of course it would be best to replace with a fresh clean fitting, but there are times when that's not going to happen....
I second the notion of doing a clean-up pass with a fitting brush, but have also had good luck starting with a 'not-so-sharp' scraper/tap made by filing a groove across the threads of a scrap nipple.

EBEBRATT-Ed

You can also make your own fake "tap" tool. Buy a long nipple the same size as the threads you want to clean up.

Clamo the nipple in a vise vertically (don't out of round it). Take a hacksaw and cut down vertically across the nipple (like you going to split it in half) until you get to the end of the threads. Turn the nipple 90 degrees and do that again.

Heat the nipple with a torch until it is red hot and tap the metal on the right side of the cut in 1/16-1/8". turn the nipple and do this 4 times

ChrisJ

EBEBRATT-Ed said:

You can also make your own fake "tap" tool. Buy a long nipple the same size as the threads you want to clean up.

Clamo the nipple in a vise vertically (don't out of round it). Take a hacksaw and cut down vertically across the nipple (like you going to split it in half) until you get to the end of the threads. Turn the nipple 90 degrees and do that again.

Heat the nipple with a torch until it is red hot and tap the metal on the right side of the cut in 1/16-1/8". turn the nipple and do this 4 times

Why heat the nipple until it's red hot 4 times?

Daveinscranton

15+ years ago I plumbed my propane lines with 3/4” black pipe.  No leaks.  Lot of joints too.  I had the bright idea of plumbing air in my shop everywhere with the left overs.  All went well until the new batch of fittings showed up (off shore manufacture).   I ended up chasing every female thread.  And discovered the miracle of at least wire brushing every male thread.  Pipe dope and big wrenches took care of the rest of it.

EBEBRATT-Ed

@ChrisJ

A small nipple you can probably heat in one shot. A larger one you might have to do the "teeth" individually.

They are good for cleaning rust and gunked up pipe dope out of old threads if you don't have a tap

ChrisJ

EBEBRATT-Ed said:

@ChrisJ

A small nipple you can probably heat in one shot. A larger one you might have to do the "teeth" individually.

They are good for cleaning rust and gunked up pipe dope out of old threads if you don't have a tap

I'm confused as to why you're heating the nipple though?
Does it help soften junk / rust etc up etc?

Corktown

@ChrisJ , I read him as saying you do this so that you can then push in on the right side of the tab that's been created previously 1/16 to 1/8", I'm guessing so that the right side 'digs in' more than the left as you turn the newly-created 'tool' in. The left side would be a 'relief' area where any debris could move into and collect during the turning in process.

O.k., @EBEBRATT-Ed, how wrong did I get this?

EBEBRATT-Ed

Yes @ChrisJ I think @Corktown figured it out. I sometimes can't explain what I mean. Making a "temporary" or "substitute" tap out of a standard pipe nipple. Not a real tap but something that can clean out rust and pipe dope and possible straighten out a dinged up thread.


Put a nipple in a vise vertical and make a saw cut like your splitting the nipple in half lengthwise. Cut straight down cutting the threads at 12 oclock and 6 oclock at the same time. Stop cutting when the threads stop. Turn the nipple 90 degrees and do it again cutting what was the 3 oclock and 9 oclock threads

With the nipple still in the vise heat the metal on the right hand side of the saw cut red hot and tap the metal in with a hammer a 1/16"or so. Do this on the other 3 saw cuts as well. When done tapping all 4 heat the entire end of the nipple red hot and toss it in a bucket of water. This will harden the metal. The side of the saw cut that was not tapped becomes the "cutter"

Use pliers obviously

Pumpguy

After reading @ranzerox post, I get the feeling he already has, or has access to, taps for the pipe sizes he needs to clean out.

I use taps all the time to clean out pipe thread tappings in old cast iron pump housings. There's a big difference in torque needed to clean out corroded threads vs going deeper, at least when dealing with tapered threads and not straight pipe threads. I'll sometimes go maybe a 1/4 turn deeper just for good measure.

Never tried the wire brush trick, but then I don't have the type of wire brushes needed.

retiredguy

@Pumpguy, I used copper cleaning brushes and cut off the handle. Sometimes I would buy a metal boiler brush that I could adapt to fit my drill.

hot_rod

The tricky part is holding the coupling to thread the tap into it, without squeezing it out of round

Thread files are another option, they are usually for the male thread

ranzerox

Here are some after snaps of using a tap, it actually worked out well as I was able to thread a bit deeper. I probably made 4-5 attempts at using the tap. Each attempt checking if I messed up.

Thanks all very much for the shares and tips! much appreciated. Going to do another badly rusted coupling and I'll share the before and after.

ranzerox

Here's another coupling I was able to take care of the corroded threads.

EBEBRATT-Ed

Some may not know this but I will just tackit on here. Rigid brand pipe taps are the best and cost$$$$$ if I really had to tap any holes for real I guess I would use them

BUT

McMaster Carr has decent off brand pipe taps and they look good. And considering 90% of all I ever used pipe taps for was cleaning old threads I can't see paying $$$$

ChrisJ

EBEBRATT-Ed said:

Some may not know this but I will just tackit on here. Rigid brand pipe taps are the best and cost$$$$$ if I really had to tap any holes for real I guess I would use them BUT McMaster Carr has decent off brand pipe taps and they look good. And considering 90% of all I ever used pipe taps for was cleaning old threads I can't see paying $$$$

Off brand?!?!
I'm sorry but Widia isn't an off brand tap.

If you want a real good tap look at the ones McMaster sells for stainless steel.  I think they're 2 or 3 flute.  

EBEBRATT-Ed

@ChrisJ

I have no idea what brand they were but I bought some years ago and the price was good. Seems like they had several selections and they were a good deal for the $$$ considering what Rigid charges at a plumbing supply house

ChrisJ

EBEBRATT-Ed said:

@ChrisJ I have no idea what brand they were but I bought some years ago and the price was good. Seems like they had several selections and they were a good deal for the $$$ considering what Rigid charges at a plumbing supply house

Here's some of their taps listed for stainless steel

They're a very well known brand for taps

ChrisJ

@EBEBRATT-Ed


I'm doing a Yamawa order this morning and wanted to show you these.

If you want to try a really good pipe tap this is what you want. They have NPT taps for other materials, but these are specifically for cast iron.