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Want to dissolve material from inside wall of copper fitting

June 28, 2009

Hi,

I'm building some shelving, and have decided to use copper pipe for the frame. I like copper because it weathers and ages so well and will look good in our house, a 1930 tudor.

An issue I am running into is this. I need copper "Tee" fittings that allow me to pass a copper pipe all the way through the top part of the "Tee."

A Copper "Tee" fitting looks like a capital T (a short one) and is like a "T" intersection on a road. One tube connects on the left to the top of the "T" bar, a second tube connects on the right to the other end of the top "T" bar, and the third tube connects to the bottom, forming the vertical part of the "T".

"Tee" fittings are 1 5/8" wide (across the top of the T) and 1 1/8" tall. "Tee" fittings are designed so that pipe goes in exactly 1/2" an inch.

So inside the top of the tee, the middle part is 5/8" wide (1 5/8" less 1/2" on each end leaves 5/8"). The inner wall of this middle part is thicker, by a very small amount, but just enough to stop a pipe from being able to pass through.

I thought that if I could use a chemical (some kind of acid?) to eat away the thicker inner wall, that would solve my problem and allow the pipe to pass through.

I've never done etching before, but reading about it on this and other sites it looks like I'd want to coat with wax the whole fitting, then expose the part I want gone to acid. This seems like it would be worth a try, but could be difficult because I'm working inside of a small tube. I'm also trying to remove a (relatively) thick depth of copper of a specific area w/o affecting the area around it. Also, I don't know how long it takes. I also saw some other articles about how you cannot ever fully remove all the acid from some metals and they'll continue to be affected, no matter how much you wash them.

That is a big explanation, but I just wanted to be clear about the what and why. My bottom line questions are, is this worth trying or is it very unlikely to succeed? What kind of acid should I use? How long would it take?

Thanks,
Ted

P.S. Below are other things I've tried.

I tried contacting manufacturers to ask if they have "Tee" fittings that allow the pipe to pass through. No responses.

I've tried drilling it out. This was not successful. The small, relatively soft / brittle "Tee" is difficult to clamp securely, and the large drill bit needed tended to just catch on the inside of the "Tee" and bend/tear it.

I've tried grinding it out. With a Dremel [on eBay or Amazon] and some grinding bits, I can grind out the thick part of the tube. This goes through a lot of bits and takes a long time.

My most successful method has been to just remove the middle part. Using a grinding blade on a table saw I grind out 5/8" from the top bar of the tee to approx. halfway through its diameter. Then I use a bench grinder to grind away the additional 1/8" or so needed. After cleaning away the excess metal bits with a wire brush, I can pass a copper pipe through the top of the "Tee." This works well enough, and does leave the fitting structurally strong enough for my needs, but I'd like a solution where I can leave the "Tee" intact more.

Ted Fines
hobbyist - Falcon Heights, MN, USA

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June 29, 2009

Hi, Ted. I think you were closest with the drill. They may not be easy to find, but there are all kinds of bits besides high speed metal drilling bits: end mills, abrasive bits, etc. The bit you used is designed for pulling the drill into the metal, and ripping the metal out and conveying it along the flutes, but that's not what you need.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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First of three simultaneous responses --

A 1/2" cylindrical double-cut carbide burr would be just right.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
June 29, 2009

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Second of three simultaneous responses -- June 29, 2009

The best way would be to use a hone, but that is slow and rather expensive, although you can get drill motor powered ones at some stores.
The best way would be to buy a reamer, this is normally a hand operation. Since it is tapered, you should ream from both ends a little at a time until you get a perfect snug fit.
Reamers used to come with different diameters and different "slopes" so look around to see what is available on the internet.

James Watts
- Navarre, Florida

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Third of three simultaneous responses --

Use a hand reamer.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
June 29, 2009