Thursday, November 15, 2012

The law of the hammer

This law is from the psychology of science and was first stated by Kaplan as: "Give a small boy a hammer, and he will find that everything he encounters needs pounding." I have fallen victim to it. Now that I know how to make a frustum of a cone with hand tools, I see the need everywhere. Let me explain.

I couldn't pass up a rusty 1" firmer chisel I found at a garage sale for $.50 even though it lacked a handle and was rusty. To my surprise, it cleaned up well with an abrasive pad and some WD-40 and I was able to get the pits out/back flat without too much effort. In fact, the back was nearly flat to begin with. It had obviously been used to open paint cans and pry out nails, but it sharpened to a keen edge quite easily.

Turns out that these cast steel tools made by William Butcher have a long and interesting history.  William Butcher made tools in Sheffield, England beginning in the early nineteenth century using the then new technique of casting steel, that is combining molten iron and carbon in a crucible at high temperature.  The steel is poured into ingot molds and then rolled into bars.  The process represented a huge improvement and led to the emergence of Sheffield as an industrial center.  (This information is from my friends at Woodnet.)  

This chisel is definitely a keeper so I needed to make a handle.  Since I don't have a lathe, I had to shape it by hand from a scrap of hard maple, not the best choice but what I had.  I watched an excellent podcast by Bob Rozaieski, showing how to do it, but guess what I thought would improve the shape:

Yup.  A cyclinder and a frustum stacked up.  I know, pretty standard, but not something I would have attempted a month ago before I learned how easy it is.  If you have never tried it, I urge you to and I will provide a brief description of the process below.

One of the nice things about making your own handle is that you can shape it to your hand, intended use and preferences.  Since I am going to use this chisel for paring, I wanted to be able to grasp the chisel firmly and push with the heel of my hand so I custom sized it.

Here's how to make a cylinder for those who are unfamiliar with it.   Start with stock  that has a square cross-section equal to the diameter of the cylinder you want and the length you want.  1 1/4" x 1 1/4" x 4" seems fairly typical for chisel handles.  Draw two circles the diameter of the cylinder on both ends.  Plane off the corners of the square until you are tangent to the circle on both ends, being careful to finish with a continuous shaving from one end to the other.  At this point the stock will be approximately hexagonal in cross-section.  Then use the plane to round over the corners of the hexagon down to the circles.

This procedure illustrates the flexibility of a hand plane.  Many of us think of using planes to, well, work on planes when, in fact, they have broad utility for shaping surfaces that are straight with the grain and convex across it.

The procedure for a frustum is essentially the same except that the circle on one end of the square stock is smaller.  Surprisingly, it is not much more difficult.

I basically combined these procedures to make my handle.  I used the method just described to make the square stock hexagonal in cross-section   I then drew a smaller concentric circle the inside diameter of my ferrule on one end and marked a line around the workpiece where I wanted the frustum to begin.  Then I used a chisel and a block plane to taper from this line on each of the eight sides down to the small circle.  Finally, I used planes to round the edges over.  I held the workpiece in a handscrew clamped in a vise.  

Incidentally, I have found that if a hexagon is what you are after, it is best to strike 45 degree lines across the corners on both ends of the workpiece tangent to the circles.  When you are making a cylinder, it doesn't matter if you don't plane off the opposite corners quite parallel and I have found that when I do it by eye I am always a little off.  Maybe your eyes are better.

1 comment:

  1. Don't think I've ever encountered "frustum" so many times in my entire life as recently and then never since high school.

    Jim B