by Christopher Cunningham
Just last year I was hoping to write an article very much like Mark Kaufman’s on making custom hardware, and the approach I had in mind was to make the process and the equipment required more accessible. I happen to have acetylene torches, but they’re expensive and not common equipment in the workshops of amateur boatbuilders. I was hoping ordinary propane torches would provide the heat required for using the silver solder I’d been using for years. Silver solder, like the 45% silver brazing alloy Mark uses, creates a very strong and long-lasting bond and is easy to use. I tried using a single propane torch to solder two short pieces of 1/4″ x 1″ brass bar together without success, then I used two torches, and then two torches with the brass surrounded with fire bricks to retain the heat. I couldn’t get it hot enough to melt the solder and I gave up on writing the article.
When Mark’s article arrived, I was inspired to give it another try. I reread Harry Bryan’s article, “Silver Soldering: A straightforward technique for joining metals,” in WoodenBoat’s July/August 2010 issue. I followed his advice and bought Bernzomatic’s TS 8000 torch with a canister of MAP gas. (The article also mentioned Bernzomatic’s TS 4000—a similar torch without the trigger and at a lower cost, but it doesn’t deliver as much heat.)
The TS 8000 has some very nice features that are a great improvement over my ordinary propane torches. A finger trigger starts the gas flowing and ignites it with a piezo-electric spark. Releasing the trigger stops the flow of gas, extinguishing the flame. That’s safer and less wasteful than a propane torch, which has a valve to control the flow of gas. The TS 8000 has a valve for adjusting the rate of flow, but you don’t need to turn it to light or extinguish the flame. The trigger has a safety lock to prevent the torch from being turned on either inadvertently or by curious young hands. The trigger also has a “run-lock” button to keep the torch operating without having to keep your finger on the trigger. The cast-aluminum body of the torch provides a comfortable grip that’s more secure than holding a gas cylinder.
The TS 8000 will burn both propane and MAP-Pro gas (propylene)—the cylinders for both have the same threads. Propane burns at 3,600° (all temperatures in Fahrenheit) and MAP-Pro at 3,730°, just 3.6% hotter [This calculation of percentage isn’t appropriate. See Comments below. Ed.]. (Acetylene with oxygen, by the way, burns at 5,800° to 6,300°.) I have three grades of silver solder with different melting points: Hard at 1,425°, Medium at 1,390°, Easy at 1,325°. With those numbers, it seemed to me that a propane torch would have been adequate for silver soldering, but it’s not the temperature of the flame that makes silver solder melt and flow into a joint, it’s the temperature of the metal. While the flame is heating the workpiece, the workpiece is absorbing some heat but losing some to radiation, conduction, and convection. To get to the temperature at which a solder will flow, the torch has to deliver heat at a rate that exceeds that of the heat loss.
The TS 8000 delivers that heat. While the opening at the tip is about the same size as that of a small propane torch, the TS 8000 has a much larger flame. It’s also louder and the grip becomes very cold, both indications that it consumes fuel faster and delivers more heat.
Even with propane, the TS 8000 did very well with silver soldering. I could get a 1″ square of 1/4″ brass silver-soldered to a 5″ length of the same material using hard solder. That’s the cooler flame working the highest-temperature solder on a workpiece larger than what I usually make.
I did another test, heating 1″ lengths of 1/4″ copper rod. With a propane torch, the copper came up to a dull glow and maintained its shape with no signs of melting. The TS 8000, burning propane, melted the copper until it turned into a ball, and, when burning MAP-Pro, it turned the copper into a ball that must have been less viscous because it rolled off the fire brick.
After reading Mark’s article I bought some Safety-Silv 45. It has a solidus temperature (below which it is solid) of 1,225° and a liquidus point (above which it is liquid) of 1,370°. Acetylene with oxygen burns at 5,800° to 6,300°. I was pleasantly surprised to see the Stay-Silv flow quickly into the joint between two pieces of brass bar and then built up a fillet as I fed more of the brazing alloy into the joint. Capillary action pulled the liquid alloy up the sides of the vertical piece. I’ll be switching from silver solder to Safety-Silv 45 for my future boat-hardware projects.
I’ve been impressed with the features and the performance of the Bernzomatic TS 8000. It will do a wide range of projects that fall between a propane torch and an oxy-acetylene torch, and for most of my projects I’ll be able to use it with propane at one-third the cost of MAP-Pro gas.
Christopher Cunningham is the editor of Small Boats Monthly.
The Bernzomatic TS 8000 is available at many hardware stores and home-improvement centers and from online retailers. The torch alone can be purchased for about $45, or as a kit with a canister of MAP-Pro gas for about $55.
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