I've just been experimenting for the first time making tension wrenches. This is what I've learned...
Hex or Allan Keys (Allan wrenches... whatever you prefer) are good BUT my first attempt failed. I used a grinder to flatten out the wrench and didn't bother to take the time to quench it as I went along. Long story short, the steel turned blue and that was the end of the strength. As soon as I tried to use it with any kind of tension at all, it started to bend.
Shortly after that, I downloaded Pyro's video on pick making (found the link here somewhere by searching) and watched him make tension wrenches from junior hacksaw blades. Well this was too cool to pass up, so I zipped down to my local "sells everything hardware related" store and bought some of these. My first attempt at bending them failed quite miserably as well. I got the metal good and hot (glowing bright orange) and made the bend, then quenched very quickly in water only to discover that the resulting tool was extremely brittle. After several more failed attempts, I discovered that my problems lay in overheating the metal. It would appear that if I heat the metal strip (after grinding off the teeth and sanding - it's much easier to sand while it's still flat) just to the point where it starts to turn the lightest of orange colors (ie, just hot enough to actually make the bend) and quench immediately, I get a very nice tool that is both hard and stable. I haven't yet successfully put the 90 degree "twist flex" into the tool, though I will keep working on it.
I hope this post saves some of you some scrap metal.
