Large Scale Central

Silver soldering: Avoiding Warpage

Tools and Tips
#1

This is the result of my latest 2 step failure in silver soldering. The only thing I ever had done before is a butane tank. That was much thicker copper and I used the oxy-acetylene torch for that and it turned out great. This time I figured thinner stock so I could get away with a map gas plumbing torch. Wrong, Didn’t develop near enough heat. It melted the flux well enough that it got liquid and every thing stuck, but certainly wasn’t soldered. So then (a week later) I got out the oxy-acetylene and gave it another shot.

crispy

So, I obviously got too much heat in one spot and melted the thin tube, but I got the other soldered pretty well. The only other problem is that the whole piece is a bit warped and not flat. I’m very comfident I could get things soldered well on the next shot, but not so sure about keeping it flat. Is .025 too thin? Or do I need the heat to be more slow and even? I default to you, the experts.

#2

You must keep your torch moving, even if you just make a small circle. Do it often enough and it becomes habit. You might have too small a tip and can’t keep the whole piece hot enough. When it is hot enough it’s easier to flow the solder to the flame. A bigger tip with a softer flame.

Apply solder to the thicker part, the thinner will heat faster and solder flows to the heat.

I like Battern’s self pickling flux, it cuts most fingerprint oils. It’s a yellow green liquid, Apply, add heat, evaporates to white then melts, metal looks clean under.

You can make a solder pick from steel wire inserted in a wooden dowel, grind tip to a point. If your solder beads up use the pick to push it down and break surface tension.

Hope this helps.

John

#3

That is pretty thin for a large sheet, I guess I have done it. I use a regular hardware store push to light plumbers torch with the yellow MAPPs gas canister with good results on prices up to a couple of onces. I only break out the oxy acetylene set for boiler work. The mapps heats more evenly. Even heat reduces warpage, but on a large sheet it is a fact of life. Small parts still heat fast in the flame, so I try to heat the big price first.

#4

Thanks guys, I think I knew and was trying most of the things you suggest I think the MAPP may be at it’s limit on this but on that try I was out doors and I didn’t build walls to keep in the heat with the fire brick, so that may have been part of the issue. I like the idea of a pick too, but that’s probably just a fix for not enough flux and poor heat. None the less valuable if needed.

I’m going to get some .030 sheet and solid strip from the store on the way home and give things another go this weekend. I really need to resurrect this phoenix of a project. I’ll report back. Thanks for the advise!

#5

Curious–why the need for silver solder? I haven’t a clue what you’re working on, but can assume it’s train-related, and if you’re using silver solder, my thoughts go towards a live steamer. If it’s a boiler or butane tank, I can understand the need for strength and heat resistance. But if it’s for a locomotive cab or something of that ilk, I’ve found soft solder to be more than adequate. If you have need to keep large plates from warping, I’d look to resistance soldering. That’s my “next frontier” in terms of working with metal. Don’t know when I’m gonna get there, but it’s on “the list.”

Later,

K

#6

Ah, the 24 dollar question. Well, it’s the cab floor for my Ruby bash which also has a new larger boiler (still in various un-soldered parts) I guess I was thinking that on a hot summer day after an hour or so of running, temps might start to get warmer than comfortable for soft solder. But seeing how effective the sheet is a wicking away the heat perhaps soft solder is in order. I used it very successfully on the tender. I’ll be trying something within the next 24 hours at any rate.

Yes, I keep looking at resistance units too. But for this loco it will be built the old fashioned way.

And yes, A build thread is coming with pictures.

#7

I look forward to the thread! I’ve never used silver solder on any of my live steamer cosmetic makeovers (mostly due to a lack of anything that would provide enough heat), but the soft stuff seems to hold up quite well anyway. If it’s something that I might be worried about, I’ll use a small screw to hold things together in addition to the solder, then–if it needs to be flat–file off the heads of the screw once it’s soldered.

Later,

K

#8

Watching, reading with interest here. Keep us posted, Eric!

#9

For this project I’d advise the Silver bearing plumbers solder, it’s a stronger soft solder and your mapp gas will work it fine.

John

#10

Randy,

A couple of observations/comments. If you can find one, a piece of high temperature ceramic to work on would be a good idea. The ceramic will get hot as you heat the work pieces, and retain that heat after the joint is soldered, therefore reducing the tendency to warp due to uneven cooling.

Working small items like you are working on, it would be a good idea to be able to heat the whole assembly to close to temperature before starting (maybe pitting it in the oven at say 400-500 degrees for a bit, again to help with even heating.

When applying the remaining heat, work the heavier part with the torch, but keep the torch moving. On your displayed part, move along the lengths of the stiffeners (I assume that is what they are). Apply SMALL amounts of solder at a time. The solder will wick down the length of the joint. It is surprising how little solder is really required on a tight fitting joint.

When you are finished, an old pot holder tossed over the part will slow the cooling process, reducing warping.

My tuppence, good luck.

Bob C.

#11

Pick

I was bench jeweler for 25 years I always had about 5 picks of different metals on my bench.

In jewelry a minimum of solder is best. I would transfer snippets of melted solder to where needed with the picks. Gold and silver solders may or may not melt (adhere) to the pic. Depending on the transfer each had a use. Sometimes with flux others without, hard too explain old reflexes. Experiment.

Before you think it a luxury… solder can float on flux. A pick is a motivator; Stick dang ye!

You’ve seen the results of more heat… burn the solder and holes.

John

#12

Also I forgot to state “Use ONLY as much heat as required to melt the solder”. Excess heat damages both the solder and the base metals, regardless of what they are. For those here with the resources, another material that can be used for models to an extent is light gauge steel sheet. Can be both silver soldered or bras brazed. The latter takes a bit of practice.

#13

A thought for a ceramic - a pizza stone for your oven. Might be a bit heavy for small parts, but then…

#14

Hey fellas lots of good tip there as well. Just take a while to get the feel, but I did some ace work today. Here is the set up that fixed the the disaster that started this thread. I decided to soft solder it all.

New Foor

It stayed nice and flat. The one on the end did move a bit once the flux melted put i pushed it back with a trusty pick.

I’ll edit this post in a bit, and add a link to the build thread once I start it. You can see what all went on top of this in the thread. Thanks again for all the help guys!

OK, here is the link : http://largescalecentral.com/forums/topic/22725/ruby-bash-1-20-3-0-4-0-build/view/post_id/265826