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Old 02-14-2011, 08:54 PM
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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.

In the time since our last session Dan cut out a second tank slightly smaller than the first one and came up with a better way of assembling the tank. I have misplaced a photo disc and may return to the business of assembly later when I can better illustrate what I'm talking about, but most basically he fits the tank sides and top long piece together, sandwiches it between two wooden forms, clamps it together with large C clamps and solders it together. I don't have the photos to show the removable tin spacers he has placed to the inside of the tank to help it keep it's shape under the force of the clamps. As I said, I'll return to this idea later when I have the photos to show. It is a great idea and does two things. First, it aligns everything together for a perfect, symmetrical fit. Second, it leaves both hands free for the business of soldering.
Another improvement over tank number one is the bung for filling the gas. I have been using a simple and inexpensive 3/4" male copper plumbing fitting on my V8 gas tanks with a brass hose cap and it has worked fine. The threading is slightly off, but it works and seals up. Dan was going to pick up an extra fitting at his local old time hardware store since he wanted to cut down the length of the fitting and remove the first few threads, thinking it would look better. The elderly woman who owns the hardware wondered why he wasn't using a brass hose coupling to go with the brass cap. She showed him one, Dan brought it home with him and the threading of course is perfect. This makes a great and inexpensive gas tank bung and cap. It needs to be modified, however, so that the hole it fits in to can be snug against the bung. Using a belt sander, Dan removed the threading from half of the coupling. It only took a couple of minutes and did a nice job. Brass bungs made for gas tanks are pricey. This home made one is less than ten bucks including the cap. I like it.
One of the photos shows the tank with the forms on it and it is being drilled out for the filler bung. Dan is using a cone shaped bit/grinder and we did the final grinding with the more precise Dremel tool. The final pictures show the bung being tinned to prepare it for soldering to the tank. This is an important step. The difference in how much heat it takes to bring the brass up to temperature compared to the tin it is going to be soldered to is considerable. The tin heats up in no time while the thicker brass will take much longer. If Dan were to try to bring the brass up to the temperature it needs to accept solder flowing into it... by then the tin around it would be so hot that his other soldering of the nearby seams would be coming apart. The tinning of the brass solves this problem. Here's how. Dan heats up the brass by itself to the point that it can be coated with tin (fluxed first of course) which penetrates down into the brass. This isn't just a glue on the surface, it goes into the brass on a molecular level. He then puts the brass bung into the gas tank hole. Now when he goes to solder the bung to the tank what he is doing is just heating it to the point that the solder flows into the tin and into the tinning on the brass bung. All it has to do is flow into the solder on the brass bung. If this isn't clear, maybe Dan can explain it better. This allows you to join the bung to the tin gas tank without all that extra heat which would wreck your soldered seams. This is an important thing to understand and will make the difference between success and failure. Thank you, Dan!
Someday when I grow up I will probably lose interest in toys with wheels, but until then...
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