solder and technique recommendation for copper plated pot metal

[Oldbuicks]

I'm needing some guidance on how to proceed with my pot metal parts. My parts have now been cyanide copper plated and are ready for me to fill the pits. Ultimately, these pot metal parts will be chrome plated. There is some good information in this forum regarding what the next steps are but I find myself needing a few more details. Like, what kind of solder do I use to fill the pits? Do I use tin/lead or go lead free? Do I use a tinning paste or just a flux and solid core wire. I think that acid core is not good but what about rosin core? Should I use a solder iron, propane torch, or butane pencil? Is it necessary to use a stainless steel brush before the soldering? My soldering experience with copper plumbing and with electronics tells me that one solder doesn't fit all situations.

My gut feel is that I will be best served by finding a solder or flux combination that easily wets the copper and that the lowest melting point is best so as not to get close to the melting point of pot metal.

Thank you for your help!

[woodjames]

I use 50/50, with a rosin core. Acid core is too tough on the substrate. The hardest part is knowing how to match the diameter to the task at hand. Lead free is a good approach but in all practicality it's difficult to work with. I've used the lead free that Caswell sells and have great luck with it now, but I've got a lot of filling under my belt.
If the copper is free of oxidation, you can go direct with the soldering, but if it's all dark, you want to just give it a rub with a scotchbrite. You can't put more than a few minutes of copper on the parts, so nothing too aggressive (same reason you can't use acid core).
Don't be too concerned about the melting point. Zinc's is a 700 or so, and solder is usually below that by a couple hundred degrees. I've also used a pure cadmium fill rod which is really low in temp and can be used direct on the pot metal.

I don't want to put things on a pedestal, but it's an art form to get solder to work well. Practice now on scrap. Not only depositing the solder, but see how it reacts when you sand it, and lightly sand blast it to, as you'll have to do that on the real piece, and it's real easy to get voids and so on in the solder that turn out to be a bear down the road if you miss them now.

[Oldbuicks]

James, thank you very much - this is what I needed to get started. I never imagined that solder diameter would be an issue but just giving it a little thought, I can now see how it would play a big part in controlling the amount of fill. Also, I see your point on tring to make future repairs atop places that were previously filled - I guess that means to get it right the first time and understand how the solder sands, as opposed to the copper and pot metal.

What do you use as a heat source for your work?

Thanks again,
Joel

[woodjames]

No problem, I learned the hard way, hopefully you won't have to also. Yeah, it's a lot more work trying to re-solder. If you repair pit "x" and plate over it, you can't try to resolder pit "x". The 1st round of solder melts and shifts, and the plate on top breaks loose - trust me it's just a big mess.

As a heat source...couple of ways of doing it, all won't be quite appropriate without experience. Start with baking the part at like 300 degrees for as long as necessary to bring it up to temp - fully up to temp. Then it's only a 5 second pass with a torch to get to the flow out temp, rather than 5 minutes with a torch on a cold part, the way that the temperature gets carried through the piece. That's probably the easiest way, but time consuming.

You can use Propane direct, but you've got to get a feel first how the heat travels though the piece. Get good at the 1st option then move to this one.

After you get down propane direct, go to Mapp, it burns much hotter - but same thing, get experience first or you'll just melt the piece, or you'll have a huge problem directing the solder. Once you get good you'll tell the solder what to do, and where to go - not the other way around (that's the art of it).

Then after mapp, you go to acetylene.

Just remember, it's not going to be the process that gives good results - it'll be your skill. Don't think that going direct to Mapp fixes the problems that you can't work out by pre-baking and propane - if that makes any sense. You'll know when you're ready to move up. You can solder to perfection with the pre-bake and propane - it just takes a while.

I never use an iron - I don't think that would be possible. I use a regular old propane torch most of the time, then I have a jewelers torch that I switch to once the part is hot. I get tons of control with that little torch as opposed to the huge flame of the big one. The jewelers torch flame can produce a needle like hot spot - it's great. You can get them on ebay, or send me $1,000 and I'll give you a signed one right before I head on vacation .

OHHHH YEAH! DON"T "FLAME THE SOLDER!"

[Oldbuicks]

I think I get it - you've got to crawl first, then walk and run. The lessons along the way get you beyond the skill and into the art - you really don't do yourself favors by skipping steps. I'm an old time chemical engineer and while I struggle with the art of things, I've learned to appreciate the dedication of those who achieve that level.

My first hobby is woodworking and for the longest time I prided myself with being able to build the straightest and squarest pieces. Then I realized that beyond the skill was recognition of wood grain, color, contrast, depth and perspective - basically the "art" of the skill.

With the exception of the MAPP setup, I have all of those heat sources including the jewelers torch. I'll get the MAPP so that I can experience the progression and perhaps someday help teach someone else.

Thanks again for taking the time to respond and enjoy your vacation!
Joel

[woodjames]

No problem, glad to help. I'm sure other questions will come up along the way, just keep them coming. That and get rid of the cyanide copper! Most of the time, you can just retrofit on a Mapp bottle, but sometimes the torches get too specific, and the weight of the Mapp causes problems with the torch. So if you can't control the flame, or it's spittin' and sputterin' could just require a different torch.

BTW...the Wood part of WoodJames - I'm a pro cabinetmaker. Seems like there's a lot of overlap there, as a lot of the people that I talk to that plate also dabble a little in wood.