Hand Tool SIG May 2010 Meeting and Field Trip

Sunday May 23, 2010

Heat Treating & Tool Making – Part I by Walter Murphy

This past May, Walter Murphy invited the KCWG Hand Tool SIG to his shop (Home Team Solutions, Kansas City, KS) for a demonstration of basic heat treating for woodworkers. Walter provided handouts detailing the relationship between the steel composition, temperature and resulting hardness or workability. As with all relationships, it’s all about the compromise.

In addition to cramming a semester’s worth of metallurgy and materials class into 30 minutes Walter also tipped us in on where to find material. Here we see an example of using the “spark test” to decide if you have high or low carbon steel.

For more information on how to interpret the sparks, see this Wikipedia article: “Spark Testing” (http://en.wikipedia.org/wiki/Spark_testing) . For the beginning blade hacker, Walter recommends purchasing O-1 tool steel from a supplier. The steel will be of a known quality unlike guessing at the composition of 25¢ garage sale mystery metal.

A very brief review of the steps:

Anneal the steel – this makes the steel ductile and easily worked. The steel is heated to its hardening temperature and then cooled slowly. We skipped this step as it is a bit like watching paint dry. Instead, if you purchase your tool steel from a distributor, it will likely arrive already annealed. Knowing how to do anneal is important because if you make a mistake during the tempering process, you can always re-anneal the steel and start over.

Shape the steel – now is the time to work the steel into shape, make the tang on the chisel or form the scoop of the gouge for instance. An important tip from Walter concerns inside corners cut into the blank. Relieve the stresses caused by the cut by drilling a hole to radius the corner first. Otherwise you run the risk of warping or even shattering your project later.

Hardening – return the steel to the hardening temperature and then quench it quickly to “freeze” the crystalline state. In the case of O1 steel we quench in oil. Used motor oil works but a gallon of peanut oil would smell less like a burned out Ford and more like your favorite drive-in on onion ring Tuesday. The steel is now as hard as it will ever be but much to brittle to hold a sharp edge. Here we see John Johnson and Anthony Ingo helping by holding a pair of MAPP gas torches.

A small forge made from a few refractory bricks makes the MAPP torches work more efficiently by reflecting heat back onto the workpiece. The simple test for knowing that the workpiece has reached its proper temperature for hardening is the steel will loose its magnetic property. Keeping a small magnet (with a large handle) handy lets you test the steel. When the magnet no longer sticks, the steel is ready for the quench. This quench must last for a pre-determined amount of time. This time will be given by the supplier of the O1 tool steel, another reason for purchasing steel of known quality when starting out.

We also see another of Walter’s tips in action. Use vice-grips to hold your workpiece, but even more important, always have TWO vice-grips handy. One pair to hold the workpiece and a second pair for gripping the piece during repositioning. This isn’t the time to be testing the thickness of your calluses.

Tempering – the final step where the steel is again heated but to a much lower temperature to relax the crystalline structure just enough to get a workable compromise between too brittle and too soft. Lacking any special equipment for monitoring the temperature, the hobbyist can use the colors that appear on the surface of the steel to gauge its temperature. A chart outlining the relationship between color and temperature will be posted in the KCWG shop. Here we see how the colors have been “frozen” by the second quench and the sample chisel blade is ready for final sharpening and the addition of a bolster and handle.

Thanks again to Walter Murphy for his demonstration and shop tour! In the very near future the Hand Tool SIG will have Part II of Heat Treating and Tool Making where we will be fabricating the blades for our own marking knives.

Rob Young
rwyoung@ieee.org
785-218-5636

Additional Photos by Rob Young