Broaching

[mrrec]

Bob:
I've seen untouched blocks with no apparent machine marks like yours. I've never liked the term "broach" as I don't think it applies to a one dimensional removal of material - keyways or holes are broached. My educated guess is that the "broach" marks everyone talks about are actually the machine marks left by a planer.

Unlike a rotary milling cutter (which were certainly in use prior to the 70's), a planer has a moveable bed which can be quite large (10'x 50' or more) so that a large number of blocks can be planed at once. The cutting tool(s) is fixed and the work piece (block) moves in relation to it. The tool "shaves" the iron in a straight line parallel to the crank. This method was apparently more economical for large production runs than milling using a rotary cutter in years past. Planers were widely used from the 1800's through WWII and are almost non-existant in production in any industry today.

I believe the planer (broach) marks could and did vary considerably depending upon the cut, tool profile, etc.

Dave