Repair of a-3 mandolin pickguard clamp

[Zigeuner]

Hello all.

I am the proud owner of a 1917 Gibson A-3 Mandolin. I inherited this from my late uncle in Columbus, Ohio in 1983 and first saw it in 1967 on a visit when he promised it to me. It's in great shape and has a wonderful "A" tone.

At that time the original pickguard and bracket, made from cellulose nitrate tortoise material had already deteriorated to dust. I've since replaced it with a unit from eBay and it looks great.

The original pickguard clamp, the one marked "Pat. July 4, 1911" was in the case pocket loose but had several nasty cracks in it. I used some low silver content brazing rod to repair it and was successful but the material I used was a bit close in melting temperature to the base material which is high copper content material called "German Silver" or nickel-silver.

I recently bought another clamp from a member here that's in much better condition than my original and was quite pleased to get it. Which brings me to my question:

Do any of you have a suggestion for a lower temperature soldering material and flux that I could use to repair two small cracks on my replacement clamp?

Any suggestions would be gleefully accepted. #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

[Paul Hostetter]

I have never seen a Gibson clamp that wasn't nickel-plated brass. Conversely, I haven't seen one that was nickel silver through and through. In either case, if you felt an urge to silver solder (braze) fissures, you a) need to make sure it is chemically 100% clean and resolderable, b) use only HARD or EXTRA HARD silver solder, and c) replate it afterwards because a correct soldering will destroy the plating.

I've never heard of "low silver content brazing rod" but anything short of hard or extra-hard solder (applied in paillons) employed with 100% effectiveness will permanently contaminate the area and prevent doing it over right. You might as well use electrical solder or Krazy Glue. In other words, there is no low-temperature solder worth considering.

[Zigeuner]

I have never seen a Gibson clamp that wasn't nickel-plated brass. Conversely, I haven't seen one that was nickel silver through and through. In either case, if you felt an urge to silver solder (braze) fissures, you a) need to make sure it is chemically 100% clean and resolderable, b) use only HARD or EXTRA HARD silver solder, and c) replate it afterwards because a correct soldering will destroy the plating.

I've never heard of "low silver content brazing rod" but anything short of hard or extra-hard solder (applied in paillons) employed with 100% effectiveness will permanently contaminate the area and prevent doing it over right. You might as well use electrical solder or Krazy Glue. In other words, there is no low-temperature solder worth considering.
Thanks. It sounds like I will use some high silver content solder. It's available, for example, in 50/50 tin/silver and has a high melting point.

Silver-bearing brazing rod is available at welding outlets such as Airgas and Praxair. I have quantities of it in my welding shop. The rods I have are 90/10 copper/silver and 95/5 copper/silver. There's also a trace of zinc and tin in the rods as well.

I won't be using superglue. #http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

[Paul Hostetter]

No superglue please! http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

Real silver solder, as used in jewelry and other refined applications, is usually sold in sheet, from which you cut little chips called paillons. These wick into the cracks by capillary action when the heating is done just right. It comes in three main grades: easy, medium and hard. The preferred term is “easy” so it doesn’t get confused with soft solders which contain tin. Once you’ve used tin, you’re finished: the metal is contaminated, and you can’t use real silver solder anymore.

- Easy Grade is 65% silver, 20% copper and 15% zinc, cadmium free and has a 1240°F melting point and a 1325°F flow point.

- Medium Grade is 70% silver, 20% copper and 10% zinc, is cadmium free, has a 1275°F melting point and 1360°F flow point.

- Hard grade is less standardized, and can run from 80-90% silver, which means it melts around 1365°F and up, barely flowing before the surrounding metal melts too. This is the stuff you really need when there’s work to be done: carbide teeth, prongs to hold diamonds in settings, broken mandolin tailpieces and pickguard clamps, whatever. It also takes the most skill and precision to be used effectively.

All these solders are really brazing alloys, and the process is technically brazing. All of them depend on super-tight tolerances and absolutely clean surfaces, they don’t fill gaps well. And they're nothing like the stuff you're using.

Whether a clamp is true nickel silver or plated brass, the solder choice is hard (also known as hard/hard!). But if you've used anything with tin, the effectiveness is permanently compromised, and the joint strength is a fraction of what it would be with a more substantial silver brazing.

[Zigeuner]

Thanks. I will get a sheet of the "easy" grade. I've seen it on eBay. The clamp has two fine cracks on the area where there are two screws that secure the clamp to the edge of the pickguard. It won't take much to do a nice repair job. The clamp is otherwise good.


Regards. # http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif