Last month I talked about electric arc welding machines and broke ground on TIG welding with the Lincoln welder that my local EAA Chapter (494) won at Oshkosh. Like many machine tools, the mere act of obtaining a welding machine only opens the door for the potential to start welding. In order to actually weld anything, and in particular in order to practice and learn to TIG weld, some extras goodies are required. Aside from the obvious, such as a welding helmet, TIG gloves, and some welding rod, you will need a stable, flat, and non-flammable metal table. (Seriously. The original Black & Decker Workmate had die-cast magnesium legs.)
Your local welding supply shop will have everything you need except a table. If you ask to see welding tables for sale, they’ll probably give you a funny “what’s wrong with you” look. Call it tradition or rite of passage, but virtually all welding tables are made by their owner/welder, and they’re all different. If your projects tend to be small, then your table can be small. If your projects tend to be big, then your welding table should be bigger.
A table is an ideal first project for beginner welders. The construction is simple, so you can focus on basic elements important to any project: organizing the material, creating a cut list, prepping the joints, and determining the correct sequence for tack and finish welding.
This project bench has a 42×22-inch top and is 30 inches tall. The design was based on the 1/4-inch-thick aluminum plate I found in the “rem” bin at my local metal supply store. I was looking for anything in the general size of 36×24 inches (either steel or aluminum). Since the rem I found happened to be aluminum, that’s what I used. Basically, anything that is conductive and reasonably flat is good for a welding table. Thickness is a matter of practicality. Plate material is never perfectly flat, but shimming a 1/4-inch thick top is a lot easier than a 3/8-inch, or thicker, top.
With the top in hand, I sketched out a base that would allow three inches of overhang around each edge (for clamping future projects) and was 30 inches tall. The frame and legs are 1-1/2-inch, 0.120-wall 1020 steel square tubing. 1020 steel is often called mild steel. Most metal suppliers stock a variety of sizes of mild steel tubing in round, square, and rectangle shapes. The standard length is 20 feet, but the dealer will cut it for a nominal fee. In my case, I purchased two 20-footers and requested they be cut into 80-inch lengths.
Unlike 4130 aircraft tubing, which comes clean and dry with a dark “mill finish” to prevent oxidation, mild steel tubing is usually coated with grease to protect it from rusting. This coating inevitably gets all over everything and makes a mess, so I like to clean it off as soon as possible using Simple Green, which is as good as any petroleum solvent and doesn’t have a nasty smell or flammability issues. It may take several paper towels and some elbow grease to get the material free of all grease and oils. You’ll know the material is clean when you can make a crisp line with a Sharpie or marking pen.
Once the tubes are marked, it’s off to the saw to rough cut to length. The closer you can get to sawing straight and square, the less cleanup is required.
With all the tubes rough cut to length, the next step is to mill the matching parts to equal lengths. Square up and clamp the parts and then mill the other ends to length. I milled two at a time, but if your vise is big enough to handle three or four at a time, that can expedite the process.
After the tubes are squared up and milled to length, the stretchers each get drilled with a small vent hole a few inches from one end. A vent is necessary on any tube that is to be welded closed at both ends. The final step before welding is to chamfer the edges. Chamfering is often used when welding thick material to get deeper penetration in the weld joint. The chamfering can be done with a file or any kind of grinder. I happen to have a disc sander, so that’s what I used.
The first welding step is to tack the assembly together. Tack welds are small spot welds used to hold parts in position. The idea behind tack welding is, because tacks afford some measure of pliability, you can tweak the alignment to adjust for weld distortion or small joint alignment issues. Tack welds also make the worst-case scenario fixable because they are easily broken and ground off if you need to redo the joint.
One thing you will notice when welding a multi-part assembly is how much welding affects the alignment of the parts. No matter how straight and square you clamp things up, welding, even tack welding, invariably knocks things off square (see detailed explanation). On a structure such as a bench, which isn’t going to the moon, it’s just something you deal with as best you can. On critical structures such as an airframe, the designer will have a welding sequence to follow in order to minimize the issue.
Start by tack welding one corner of each joint, checking for square and then tack the other corner to secure the joint. Then move on to the next joint until the whole assembly is tacked.
Once the assembly is completely tack welded, you can finish weld each joint. The sequence is a bit like lighting a birthday cake: start at the far end and move toward you. Do this mostly to avoid getting burned by having to reach over a hot joint. Never quench or spray the weld with water to cool it off. Let the welds cool down before flipping the project or re-orienting the work to weld in fresh areas. Once the frame is welded up, fit the top to the bench with some countersunk flathead screws and you’re ready to roll!
Tack welding the long cross stretchers to the top caused the assembly to warp out of alignment. It was necessary to add some clamping pressure to realign the bench for the final tack welds.
Bob Hadley is the R&D manager for a California-based consumer products company. He holds a Sport Pilot certificate and a Light-Sport Repairman certificate with inspection authorization for his Jabiru J250-SP.