Sunday, March 20, 2011

Using Tool Steel

Yesterday I forged a slitting chisel and an opening chisel for the fly press for a future project. I chose H-13 tool steel for the job. The only alloys I buy are H-13 and S-7. From time to time there are opportunities to pick up free of charge some used trenching bits for hardy tool blanks or some coil spring or a torsion bar but I don't buy them. Years ago I placed a couple of orders from a major supplier and paid the premium price but in recent years I have always been able to find what I need at a tailgate sale for a very reasonable price.

I picked a 1" round bar of H-13, heated it in the coal forge and forged the shape of each chisel in a single heat on the power hammer. The rest of the work was done with the bench grinder, flap disc and belt sander, silicon carbide wheel and finished with the hard felt wheel dressed with chromium oxide polishing compound.

I welded it to the fly press top tang in proper alignment. I first tacked it in one edge spot with the MIG welder with a short bead which I can bend cold while the tool is in the fly press adjusting it's position before the final welding. When it was finished I heated it up above critical and let it air cool.

The tool steel probably cost $2 and it took about a half hour to complete. The process is really so quick and economical it is reasonable to plan on making exactly the right tool for each job.

That leads to the issue of dedicating tools. I have a number of items I make time and again so it seems easiest to dedicate the small tools, jigs, blanks, etc. and store them together until the next time I need them. If I know the tools will be used infrequently for short runs that leans me toward using my "free" tool steel for the edge tools. Many don't need any heat treatment but occasionally one needs an oil quench to harden enough. For the swage type tools water quenched mild steel works well in most cases.

For completeness I should add that I did buy some 4140 annealed die stock for my Smithin Magician and have made several custom dies. The instructions for heat treating came with the material and are as follows.
Normalizing: Heat to 1600/1650°F (871/899°C), hold for 10 min. and air cool.

Annealing: Heat to 1550/1600°F (843/871°C), pack in lime or wood ashses until cool.

Hardening: Heat to 1550/1600°F (843/871°C), and oil quench.

Tempering: After hardening, heat to a temperature 400°F to 500°F and air cool.
I'm sure that's really useful to anyone who has a heat treating oven but I don't. The dies I've made have enough radius on the edge that hardening hasn't been much of an issue so just heating and oil quenching by guessing has worked OK. Some call that the SWAG method, the educated guess, intuition or just guerrilla metallurgy.

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