Hand Tools

Support for Warren’s analysis *PIC*

Wiley Horne--So. Calif.
Hi all,

Warren’s explanation of the combined effect of chipbreaker setting and geometry seems to be borne out by studies done by Professors Kato and Kawai of Yamagata University. A few years ago, Bill Tindall arranged for Ms. Mia Iwasaki to translate one of the 1989 papers into English. Bill and Steve Elliott edited and published the translation on Steve Elliott’s website:


The data were generated by a machine planer, taking 0.002” (2 thousandths) shavings from a birch species, with the cutting iron bedded at 40 degrees, and the chipbreaker set back to 4 thousandths or 8 thousandths. The control was ‘no chipbreaker’.

Figure 6 below shows the horizontal and vertical forces at the cutting edge. The horizontal force, P-sub h, is the force required to take the shaving—in a hand plane situation it would be the pushing or pulling force. The vertical force, P-sub v, acts downward initially as the sharp blade is pulled into the work, then goes positive, as the blade dulls and must be held in the cut.

In the legend, the chipbreaker setback distances of 100 and 200 um (micrometers, or microns) are approx. 0.004” (4 thousandths) and 0.008” (8 thousandths), respectively.

The upper part of Fig. 6 shows the horizontal forces, for setbacks of 4 and 8 thousandths, and for 40, 50, and 60 degree angles on the chipbreaker face.

In general, there is a sharp increase in ‘pushing’ force in tightening up from 8 thou to 4 thou, but as an exception note that the pushing force for 4 thou/40 degrees is quite close to the force required at 8thou/60 degrees. These specific figures are of course particular to the Kato/Kawai setup, but qualitatively they seem to bear out the more general principle Warren stated—that the shaving is hitting the breaker higher on the bevel at 8 thou than it is at 4 thou.

Warren also made the point several days ago that you want to use the farthest setback that works. Note in the horizontal force data that there is a sweet spot around 8 thou, while the pushing force increases by about 50% (with the exception of the 40 degree bevel) when the setback was tightened to 4 thou.

As a side comment, the vertical force data seem to show that the 4 thou setting led generally to faster dulling, as the cutter stopped pulling itself into the work quite a bit sooner at all the 4 thou settings, except the 4 thou/40 degree setting where there was less breaking effect.

Pardon this long post, but I was struck by how the data lined up with Warren’s analysis.


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