Making Small Tools

Jennifer Shirley wrote: I got my tool-making supplies, and headed for the shop. I discovered that I had bought air hardened drill rod. What I'm attempting to do is make a few gooseneck scraping tools out of some of it. Like the small Sorby ornament tools. No bits attached, just grind the drill rod to be used as the scraper, then bend the gooseneck into it . My question is: since this is air hardened, does this mean that after heating it to red hot and bending the gooseneck that I just let it air cool? No oil or water quenching? And refresh my memory: that process, the quenching or air cooling, is called tempering? or hardening? Or are those one and the same?

Raymond Overman in SC: I just made this small boring bar with ¼" x ¼" x 8" M2 bit from WT Tool. I recycled the handle from an old beat up second hand gouge. I rounded over the corners with a belt sander. Total cost: $1.35 + tax

I've got another piece of it that I'm going to heat about half an inch below the tip and add a 45° end to. Since it's M2 already, I shouldn't have to temper and harden the tip I hope.

Ken Grunke from SW WI: Jennifer, the quenching is called hardening, which leaves the metal in a very brittle state. So it has to be tempered to take the brittleness away by gently heating at a low temperature, in the range of 400 to about 600° Farenheit depending on the desired hardness. The temperature is judged by the oxidation coloring on the metal's surface as it's being heated, ranging from a very light yellow, through brown, to purple.

So, after the hardening quench, first thing you should do is check to see if the air-hardening steel actually was hardened. If a file skates across it without biting in, you're good to go. If it bites in, there's no sense in proceeding with the tempering, you'll have to try another method of hardening which I'll go into below. But first I'll describe the tempering process.

Polish the metal with a scotchpad or fine sandpaper so you can see the oxidation colors. Then heat slowly, gently, and evenly with a propane torch or a gas burner on a kitchen stove, using a low flame. It must be done slowly to allow the heat to penetrate into the middle of the piece, not just on the surface. Otherwise the outside may be tempered but the core will still be brittle. You need a good light to see the colors well. For a woodturning tool, a dark yellow, not quite brown, is appropriate. It's still quite hard and will keep a good edge but is much less brittle. If you get to blue, you've gone too far and must start over with the hardening. Once you get to the desired color, quench in water to halt the progression of heat, and you're done.

Now, if the hardening was not successful, you could start over and try water or oil quenching. Air-hardening steel is not so drastically different from water- or oil-quenching steel that these methods won't work, so it's worth a try. Water quenching is likely to cause cracking of the metal, but oil quenching is more gentle and less likely to cause cracking. Alan Lacer used olive oil when he demoed hook tool making for our club, any vegetable oil will work but olive oil is less likely to catch fire. Just don't use motor oil, it's bad stuff for this.

And if this doesn't work, your best bet is to get oil-hardening steel, you should be able to get that locally if you're in or near any city that has a machine shop who can refer you elsewhere if they don't stock what you need.

One note about heating metal red hot for hardening: If you don't heat it hot enough and long enough, you're wasting propane or whatever you're using. A rule of thumb is to hold the heat for 1 hour per inch of thickness so a ¼" rod should be held red-hot for 15 minutes to allow the heat to reach into the core. How red-hot? Just past the point when the steel loses its magnetivity and not much higher, or you risk burning the steel. A bright orange is close to being too hot.

John Lucas: What follows is for oil hardening or water hardening and may not be accurate for air hardening. I agree with Ken or whoever said it that you can't hurt anything by trying the techniques mentioned on the air hardening stuff. This steel is good enough that even if you don't do anything it will still hold a half way decent edge. I've never kept a tool that hot for 15 minutes. I heat it until it's non-magnetic and then quench it. Takes less than 30 seconds with a MAPP gas torch. Ken's method may be the official way but I've made lots and lots of tools using this technique.

To temper the metal I find it easier to just put it in the oven at 425° and let it sit for 30 minutes per ¼" of thickness. At the end of the 30 minutes just turn off the oven and let it cool.

It should come out a nice straw color. If you want to heat it with a torch I do it one of two ways. I heat it very gently until it turns a light straw color or I heat it more aggressively about 1" from the tip. It will start to turn yellow and then purple. Watch the yellow creep toward the tip and then quench it. That's the blacksmith way of doing it. I still prefer the oven.