Last winter I built a bunch of display cases so the Hamilton Museum could show off more of their wood type collection. I looked at the Wish List a while ago and saw a need for strong tables for workshop areas. I figured maybe I could make some.
I know wood working well enough to make some tables, but strong tables made out of wood would probably be quite heavy. So I thought I should try making a table out of steel to see what design would work to be strong and light weight.
I joined a hackerspace in Chicago two years ago. It’s a place with lots of tools and benches where members can work on whatever kind of building project they like. It’s sort of like having your own shop but quite a bit bigger. The tools include every kind of power tool there is, from metal cutting bandsaws, lathes and welders to wood planers and table saws.
I got a short introduction to arc welding four months ago. Then I practiced for a month and decided I liked welding enough to get my own welder. I bought a good welder along with a helmet, a leather jacket and gloves. The helmet protects my eyes from the intense ultraviolet light generated by the welding arc.
Welding is dynamic compared to woodworking. Things are melting and flowing at very high temperatures. It’s fun to watch welding, even as I’m doing it. There is a good deal of science in welding but the people who need to know that are the ones who build welding equipment. In short, what happens is the welder makes a short circuit on purpose to make a high temperature electric arc and that melts the steel.
The practical side of welding is it melts steel instantly. To do this the welding arc temperature is around 5,600 degrees. The electric arc is shielded from the air by two inert gases, argon and carbon dioxide, which spray out to keep the weld from rusting. A weld will rust as fast as it forms if it is done in the air. A rusty weld is worthless, like full of holes. It can just crumble away. After doing a weld, it takes the parts a while to cool down, so I don’t rush to pull the clamps. I need a lot of clamps to hold the parts in place so I can weld them together. I got eight Vise-Grip clamps that have great big jaws and no teeth to hold the cross bracing in place.
I have been welding for a couple months now and I can see the welds in progress as the steel builds up across the joint. Now I can tell if a weld is going well or if it looks bad. When a weld looks weak I just weld over it to add more steel. Some welds get to be downright ugly by the time they are finished, but ugly welds hold just as good as pretty ones.
I built the table frames using three shapes of steel; flat strap, angle and square tube. The square tube is very strong and won’t flex at all no matter how much force is applied. I designed the frames to be as rigid as possible. Moving the legs in from the corners by a few inches helped increase the rigidity at lot.
Tensile strength is one of the strength tests of metals, where a piece of steel is stretched between two points. A tensile strength rating for common steel is 45,000 pounds per square inch. Steel is very strong. The kind of welder I have will work with steel up to 1/4 inch thick. The steel I used for the table frames is 1/8 inch thick and 1 inch wide.
I ended up making twelve tables 40 inches square and four tables 40 inches by 8 feet. After I got going and gathered the tools and clamps I needed, the actual production went fast. I made three of the 8 foot frames in two days. I took the frames up to the museum and cut sheets of plywood to size to make the tops. It has been a real fun project and I’m sure I’ll keep welding other things for my own use.