Soft Soldering Tutorial

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Soft Soldering Tutorial

Postby blond.chap » Tue Jan 08, 2013 4:08 pm

Soft soldering is (in my mind), the best way to put a copper still together. If you're like me, it can seem a bit intimidating when you haven't done it before, but it's quick to learn and pretty fun when you've got it worked out. "a few safety things"
- Make sure your soldering area is clear of anything flammable (wood, spare butane containers, >40% ethanol, running still, etc.)
- Wear safety goggles, solder occasionally spits
- Wear closed shoes

1. Dry fit parts and make sure that you can keep them in the required position while soldering
2. Clean joins well (using rasp, rotary tool, grinder), finish with emery cloth to rough it up a bit
3. Apply flux onto both pieces at the point that they’ll join, leave for a few minutes before applying heat
4. (optional) to stop the solder flowing into places you don’t want, draw a line with a graphite pencil (thick builder’s pencil), solder won't want to pass over this line.
5. Start heating the pieces with a butane torch. Never heat the fluxed join directly or you’ll get little burnt bits of flux and the solder will not stick. Heat the larger of the 2 pieces about an inch away from the join, constantly move the heat around the piece so that you evenly heat it.
6. Once the flux starts evaporating you’re getting close to it being hot enough, place the solder at the join on the piece you expect to be coldest (if you've mainly been heating the larger piece, place it on the smaller), and continue to heat the piece that you’re not touching
7. Once the solder starts melting, slow down your heating by moving the torch further away from the piece, heat very gently from now on (if you over heat the solder won’t flow properly).
8. When the solder has flowed into the join, move the heat around the piece to a place where there is no solder, a light touch with the solder should now have it flowing easily
9. Once there is solder all around the joint, remove the heat. Then take a wet rag and gently wipe it around the join to remove excess solder.

If the solder isn't flowing into and sealing the join properly, one of the following is likely happening:
Problem 1: One or both of the pieces aren’t hot enough. Solder is sticking to one, but not the other, or not melting at all
Solution 1: Keep heating gently by moving the torch around the piece. If there are 2 similarly sized pieces, spend about 50% of the time on each. If one is significantly larger, spend 95% of the time on that, 5% on the other. The larger piece will heat the smaller

Problem 2: One or both of the pieces are too hot. Solder is flowing too quickly, and pooling at your feet.
Solution 2: Let the pieces cool, heat more gently and check frequently whether solder melts at any point. Make sure you’re using a butane torch (Map or oxy heat too quickly)

Problem 3: One or both of the pieces wasn’t cleaned and fluxed properly. Solder is flowing ok but is only sticking to some places and leaving gaps at others
Solution 3: Heat the pieces to melt all the solder, and separate them using pliers (not fingers). If there are beads of solder, get a wet rag and wipe them off while hot. Reclean the piece with rasp, benchtop grinder or rotary tool as appropriate. Finish with emery cloth to get it a bit rough. Reflux and start heating again gently. Don’t waste your time and solder trying to get more and more solder into a dirty join, trust me it doesn’t work

Problem 4: The piece was cleaned and flux properly, but you’ve burnt some flux Solder may be sticking to some places, but leaving gaps, you can see some black bits on the join that weren’t there when you started heating
Solution 4: Reclean as above, when heating next time keep the flame a bit further away from the join and be very careful not to pass it over the join

Problem 5: You’ve got the wrong solder or flux. The flux isn’t melting when the solder does, or the flux is burning before the solder melts (even when you’re careful about heating)
Solution 5: Make sure you have the right flux for the solder, e.g. don’t use a silver brazing flux with soft solder, or silver brazing rods with solder flux.
If you’re still getting troubles, try different brands of flux and/or solder. Aquasafe solder (made by consolidated alloys) with Bakers liquid flux works for me. Bernzomatic plumbing solder also works ok with their paste flux.

Problem 6: The gap between the pieces is too wide The solder may be melting fine but falling through a largish gap.
Solution 6: Solder is meant to flow with a very small gap (<1mm is preferred, but can work up to max 2-3mm in my experience). Either:
- Try to reposition the pieces to get a smaller gap;
- Cut a thin strip of copper to place in the gap; OR
- Remake the piece that is too small
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