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I'm trying to solder a soft copper coil to a regular fitting and its not working, (I did already a lot of soldering and never had a problem) is there any tips or tricks for soft copper? Do I have to work with it in a special way?
Thanks for any reply.

  • Does it fit nice and snug? There are different types (size schedules) of "soft copper". – Jimmy Fix-it Sep 28 '16 at 4:26
  • @JimmyFix-it The schedules effect the wall thickness and inside diameter but not the outer diameter. 1/2" copper tube for plumbing is 0.625 (5/8) inches outer diameter no matter tube type such as K, L, M, etc. The copper tube handbook from copper.org can confirm this. – Mister Tea Sep 28 '16 at 12:20
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    What does "not working" mean? – isherwood Sep 28 '16 at 12:57
  • Check that the section of tubing is round. I have had trouble with copper tubing getting small flat areas on the outer edge of rolls, or getting deformed when cutting. If its deformed that could explain the issue. – user2448131 Sep 28 '16 at 13:34
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    I use a swaging tool to fit soft copper on HVAC systems. The sizes are not measured the same (id for hard copper pipe and od for soft copper). because of the small surface area in contact I use silver solder and flux. There are lower temperature solders but they wont hold up to vibration as well. – Ed Beal Sep 28 '16 at 13:42
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My guess is either the joint wasn't cleaned enough and/or not fluxed properly. I have had problems when my old tub of flux got dirt in it. When heating, the dirt burned and ruined the flux preventing a good solder joint. Check your flux and flux brush for dirt and replace or clean as needed. Then clean all of your joints thoroughly with one of those wire brush cleaners for copper tube or scotch bright.

  • I did a few joints after that one with the same flux and cleaned with brush and emery and all of them are good. – aofkj Sep 28 '16 at 15:20
  • @aofkj As others have stated above, check for deformation of the tube ends. – Mister Tea Sep 28 '16 at 15:34
  • also ... compared to the other joints that came out ok, were any of them as heavy as either of the 2 parts you are currently soldering? the more material, the more heat you would need on the larger part to form a equal temp between the two parts and a good bond. – noybman Sep 29 '17 at 4:10
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File the soldering points, and use a 1300W iron. If you can’t use leaded solder, go higher. Preheat the pipe for a minute.

  • Silver solder would be better than regular solder . however regular solder works well with a torch but it is not strong enough for HVAC. I know the OP did not say what this was for. – Ed Beal Sep 28 '17 at 23:16
  • @EdBeal Yes, it’s also poisonous. – user2497 Sep 28 '17 at 23:18
  • Silver solder is not poisonous and there is regular solder for plumbing ,,, I was not referring to electrical grade 60/40. – Ed Beal Sep 28 '17 at 23:20
  • @EdBeal I meant regular solder was poisonous. I agree with you. In any case leaded solder should only be used inside enclosures. – user2497 Sep 28 '17 at 23:22
  • What does go higher than leaded solder mean? Octane? Sorry, just joking. Please clarify. Also note there are different mixes with different melting points. As otherwise hinted here, clean the pipe with a brush or better yet a 800 grit wet paper. then use flux. VS. just "heating for a minute" heat the pipe just until you see the flux steam/bubble then introduce the solder to the point of pipe and iron with it applied to the pipe. Be sure both joints were prepared and heated evenly before applying solder. – noybman Sep 29 '17 at 3:25

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