Article And Photos By: Will Ramsey
Originally Published In The February 2013 Issue Of Cycle Source Magazine
In this month’s tech article, I am finishing up the polished aluminum gas tank replicated for Bobby Seeger (Indian Larry Motorcycles). The original tank was designed and built by Lock Baker (Eastern Fabrication). Unfortunately, the tank endured a high speed impact with the pavement and was heavily damaged, but never leaked! Not wanting to cut up Lock’s tank, I decided to replicate the entire tank, holding true to the original design. Last month’s article demonstrated the use of a flexible shape pattern to replicate the two sides of the tank. This month I will show you how I form the center section of the tank and weld the panels together. I chose to use 3003 H14 aluminum for the combination of strength and formability. The proper welding rod for joining 3003 panels is 1100 alloy rod. 1100 alloy will allow for ductility along the weld seam (4043 likes to crack if it is worked) and provides the best color match when the tank is polished. I will be using the TIG to weld the aluminum panels in order to replicate the design of the original tank. There is some debate as to the best way to weld aluminum sheet metal. I often use the oxy-acetylene torch and flux to weld thin aluminum, due to increased workability and weld density, but I also use the TIG welder (with a purification system) when appropriate. Both have advantages and disadvantages and truly deserve a tech article devoted to that debate and the proper techniques of each method … Keep an eye out for that one.
In order to form the center of the tank, the distance between the welds must be measured. The taper will be cut later so for now a 7” wide rectangular piece is cut.
It takes a bit more horsepower to form the panel without annealing the aluminum. This method, however, will maintain the strength of the material so that the panel is not easily dented on the road. Care is taken to form a smooth flowing curve.
The form of the center panel must follow the outside edge of the side panels as closely as possible. Time must be taken here to get a very good fit. The final highly polished finish of the tank will magnify any mistakes in the alignment of the panels.
Once the center panel is formed, the taper must be cut. The measurements illustrated in the first picture reveal that each panel tapers 1.25”. Therefore, with the front of the panel elevated 1.25” off of a flat surface, a height gauge is used to scribe a perfect trim line. The process is then repeated on the other side. When sheared, this results in a symmetrically tapered center panel.
The key to welding aluminum sheet metal is cleaning, cleaning, cleaning! A solvent like acetone (or rubbing alcohol) is used to clean the inside and outside edge of the panels to be welded. A new stainless steel brush is used to scrub the edges of the material to a bright finish.
When the welding rod is formed, it is drawn through a die which has been lubricated with a wax or graphite based lubricant. A brand new welding rod will reveal these contaminants when cleaned with acetone.
The panels are lined up with an excellent fit so that fusion tack welds can be used to hold them in alignment. The tack welds are placed no further than 1” apart. These tightly spaced tacks will help to minimize warping and misalignment along the weld seams.
Once the entire weld seam has been cleaned again with a stainless steel brush and acetone, the final weld can be made. The welds on this tank will not be metal finished so any inconsistencies will be evident to everyone.
After welding all the panels together, the tank can now be compared to the original gas tank.
After welding in the filler neck … and the petcock bung … and spending half a day wet sanding and buffing … the new gas tank is finished!
And finally, a fun-filled trip to Indian Larry Motorcycles (Brooklyn, NY) to mount the gas tank and eat bagels … and pizza … and pastrami …