Hand Tools

Cut depth and cap-iron set redux

Patrick Chase
I redid my experiment exploring achievable cut depths as a function of cap iron setback, this time measuring wood removed instead of shaving thickness.

To recap, I used an 8" x 1.5" curly maple [*] specimen, and took increasingly thick shavings until surface quality was noticeably degraded. I measured thickness in a fixed location before and after each pass.

This time around I used a 4-1/2 with a stamped-type cap iron. Bed angle is 45 deg, and the steepest part of the cap iron's leading edge was 50 deg. The tested setback this time was 5.5 mils, measured using a camera with a scale in the frame for calibration. The cutting edge is therefore 5.5*sin(45) = 3.9 mils "deeper" than the leading edge of the cap iron.

I was able to take cuts up to 4.2 mils deep with moderately increased planing forces and without significant surface quality loss. I was able to achieve cuts up to 5.2 mils deep with greatly increased force and modest dulling of the surface.

The upshot is that cuts with the leading edge of the cap iron at or slightly below the plane of the sole again proved feasible and usable, though both planing forces and quality suffered when going significantly deeper. I'm becoming more convinced that profiling the corners of the cap iron can be a reasonable thing to do (though I'm still not doing it myself as I don't want to add another variable to my setup right now).

One interesting note is that the difference between shaving thickness and cut depth proved to be depth-dependent. For example, a 1.8 mil deep cut produced a ~2.1 mil shaving. A 4.0 mil cut produced a 4.2 mil shaving, while the aforementioned 5.2 mil deep cut produced a 5.2 mil shaving (no detectable difference).

[*] Acer macrophyllum as far as I can tell

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