Note the copper will tarnish rapidly. You can get a quart of tinning solution for a few bucks, dip the copper into it and it'll have low resistance properties just like raw copper but less likely to tarnish. And just as solderable as clean copper.

Cheaper yet, polish the copper and give it a coating of mineral oil. The contact resistance will still be OK, and a drop or two after use will keep it OK. Also, I think that copper oxide is fairly conductive..
And even if you ue steel wool on it each time it will still lat many years.

 

Clean with a mix of vinegar and salt.

 

If you chose to ue a stainless steel tube, it would be a simple matter to solder the wire lead to a piece of spring and force it inside the tube. That would solve the problem very well, and without a lot of heat. And it could be changed rather easily when desired.

 

Taking step back
I seem to have missed,
are you sending current around the loop to read, or reading current generated form else where ?

If your sending the current out, then the resistance within limits of the tube / contact does not matter.

 

I am going going to put the extra money and buy the copper pipe to get better results.

I was into these years ago still have Clark's book. The one I made didn't seem to work for me so it was given to a friend. Instead of the copper pipe, I used two wooden dowel rods and wrapped bare copper wire salvaged from some leftover house wiring jobs around the dowels and soldered the flexible wire from the circuit to one end of it.

People saying just tin the copper to keep it from tarnishing seem to forget your are then exposing yourself to the lead solder from the tinning process. That is then going to over time get into a whole other problem.

 

Hello,

How about an expansion bolt inside the tube?
https://www.google.com/search?q=exp...nt=img&ei=KCrfYL_2N4GM9u8P4aCeoAw&safe=images

You could mount an eye on the bolt for the electrical connection.

Bertus

 

Hello,

How about an expansion bolt inside the tube?
https://www.google.com/search?q=exp...nt=img&ei=KCrfYL_2N4GM9u8P4aCeoAw&safe=images

You could mount an eye on the bolt for the electrical connection.

Bertus

I suggested some sort of springy arrangement inside whatever tube is used. Tinning the copper tube makes it much less nice to handle, in addition to the reasons already mentioned. But it could be plated with chrome, nickle, silver, or even gold.

 

The spring and expansion bolt are very nice and fun solutions, you must have very creative minds to think about this kind of stuff
Yes as you said Shortbus I'd like to avoid being in contact with harmful metals since some toxic elements could cross the skin barrier, under the effect of the current and water/sweat.
Rolling a copper wire on wooden rod seems tempting indeed, but I prefer the plain copper pipe to get a nice contact surface with skin.