Hand Tools Archive

Traditional cap iron construction

Steve Voigt
Here's something that can be filed under "totally esoteric stuff that no one cares about."
Last week, I made my first traditional cap iron, and I'm making another today. By "traditional," I mean the type used with tapered irons in wooden planes. The bend is about 5/8" from the bottom, and the end is shaped in a gentle radius, whereas modern cap irons are bent in the middle, and often just have a flat bevel.
Before making one, I measured of bunch of old ones I have, and more or less copied the dimensions. There was one thing that really struck me though, which is the location of the threaded hole.
On a typical old chipbreaker for a 2" iron, the length will be about 4 3/4", and the hole will be about 2.75" from the bottom. From an engineering standpoint, I would think you would place the hole right at the midpoint, which would be 2 3/8." You would get more pressure right at the cutting edge that way. However, none of my old chipbreakers do this.
The only explanation I can think of is that they didn't want to get too close to the bottom of the slot, but on every iron I have, many of which are full length (or very close), the hole could easily be placed 1/4"-3/8" closer to the edge.
I'm not suggesting that they "did it wrong;" in my experience there is always a good reason things are the way they are on these old planes. I just don't know what that reason is.
If anybody is still reading this and hasn't lapsed into a coma, do you have any theories about this? If you do, I'm all ears.

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