metal

This is a weld-on tank bung; a means of attaching pipe threads to a vessel. It is intended to be welded onto the wall of a tank or pressure vessel, providing solid pipe threads in a material typically too thin to be tapped for pipe threads. On some occasions I've used them for that purpose. On others, I've found that they make a great component in pneumatic cannons. More on this obscure part after the jump.

Since we inaugurated Guess This Tool, you've all proven way too hard to stump, so for this week's contest, we're mixing it up a bit and giving you a mystery part rather than a tool.

Take a piece of tissue paper. Support the edges and press down on the center to form a bowl. The ripples that will form are extra material with nowhere to go. Now imagine the tissue was metal and you see one of the essential difficulties of putting compound curves (as opposed to a simple curve, aka a fold) into sheet metal when you need a little impression and don't have a stamping machine handy. But if you know exactly where and how to hit, you can do it with nothing more than a mallet and a tree stump.

Bent tubing is key. Roll cages need it. Tube frame chassis need it. Even the storage arrangement for my welding clamps needed it. There are a number of ways to go about bending tubing. Rotary draw benders like the Hossfeld Universal bender make a tight bend at one point. Three-roll benders create more gradual curves. But none of them compare to this automated CNC tube bender that just spits out steel in any shape you want. I could watch it all day.

Whenever you run into a snag on a project, it's a pretty safe bet that somewhere there is a grizzled old man who's solved it many years before you and will be happy to tell you it. That's why I never miss the chance to chat up the old guys working at or just hanging around lumber yards, machine shops and scrapyards. I always walk away smarter.

One recent example: While helping PopSci's John Carnett with his Green Dream house, we had to make a number of bolt holes in thick structural steel. (I would have preferred that the beams had come from the steel yard properly cut and drilled, but sometimes things don't work out as we'd like.) The drill just wasn't cutting it, so I turned to the oxy-acetylene cutting torch. It would easily pierce the thick steel, but I wasn't sure it'd cut clean holes. Then I remembered a great trick for burning accurate holes that I learned from an old-timer at the structural steel yard.

A metal that reacts with seawater to produce an electric field may help keep sharks at bay. But the idea isn't to protect humans from shark attacks. Just the opposite: scientists hope the metal will save sharks from senseless deaths in fishing nets.

An estimated 11 million to 13 million sharks die each year as "bycatch," collateral damage in the hunt for other fish. Sharks grow slowly and can take many years to reach reproductive age, so their populations are being severely impacted by fishing.