Woodworking with Diego de Assis

  Shop-made Thread Cutting Tools for Wood 3 of 7  

I used a piece of an old file. Files are made of good high carbon steel, and they can be used to make various cutting tools, such as gouges and chisels. There are several types of scrap steel with high carbon content that can be used, but how does one measure it?

A quick test is to grind the metal and observe the sparks it gives off. High carbon steel gives off many sparks. Just touching it to the grinding wheel produces a small “explosion.” Low carbon steel, in contrast, gives off few sparks. In the photos I compare an ordinary bolt of low carbon steel (above) with a piece of an old file (below).

Another test to heat the metal to the point at which it loses its magnetic attraction (cherry red), quench it immediately in oil or water, then try to file it. If after this hardening procedure the file skips, as if it were sliding on glass, it is high carbon steel, which can be hardened and tempered.

To test for the desired temperature, simply touch it to a magnet while it is still cherry red. When it does not stick it is hot enough to harden by quenching.

In an improvised forge made of bricks and a propane torch I heated the metal to the cherry red non-magnetic point, then let the piece cool in the air, without quenching. This anneals the metal, so that it can be easily worked.

To shape the “V” in the cutter blank I clamp it in a vise and begin with a shallow hacksaw cut to guide the triangular file used to finish the job. Then the external shape of the “V” is formed. Interestingly, the metal is very soft, making it impossible to sharpen the edge.

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Starrett Tools



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