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Old 02-27-2011, 08:40 AM
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silverbear silverbear is offline
The Boy Who Never Grew Up
Join Date: Jul 2009
Location: northeastern Minnesota
Posts: 8,131
Default Re: Tinsmith's in frame gas tank for cantilever Schwinn.

We have cut our long top pieces on the sheer and then mark the spot where the gas filler will go. Dan is going to the right side of the tank as the others have been and I'm doing mine on the left side. He punches a hole for the brass bung, but doesn't have a punch large enough. The ideal would be to have a 3/4" punch and in a few seconds a clean hole would result. Instead he uses the largest punch he has and then reams it out to size using a cone shaped metal bit. While he opens his to 3/4" I do the same with a Dremel type rotary tool and a grinding bit.
Dan tins the brass bung where it will be soldered to the tank and also tins the copper at the hole it will fit in to.
He places Big Bertha on the top of the brass bung to heat it up to the point the solder flows... and waits...
As we wait Dan talks about how the copper is different from the tin. His area of expertise is tin work, but has worked with copper off and on a bit through the years and knows the soldering process is different due to the difference in metals. The tin heats up quickly and allows you to get in and out quickly enough to get the job done before too much heat migrates to other areas of the tank, possibly melting previously soldered joints. The copper tends to suck the heat out from where you want it and kind of generalizes the heat. It is one reason we are doing the bung on the top piece before it is joined to the side pieces. You can see the logic in that there is no danger in melting seams if the seams have not yet been made.
We are still waiting for the solder to flow as Dan remarks on another difference between copper and tin. The tin bends are more crisp while the copper makes a more rounded bend, I'm guessing because it is more malleable and is more willing to stretch.
Dan decides that Bertha is not up to the task of heating the solder enough to flow... the brass is dissipating the heat before it can get to the lower portion of the bung and make a union with the tank.
This is the one time in this tank making that Dan fires up the propane torch and applies the flame directly to where the bung joins the tank. Done in a few moments with a solid joint.
Now we can start putting the tank together... coming up.
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Someday when I grow up I will probably lose interest in toys with wheels, but until then...
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