03 February 2014

Kato and Kawai video

Like many others I have seen the Kato and Kawai video.  The video looks at a usable back iron set between 0.2 and 0.1 mm for shavings of  0.05 and 0.1 mm And if I go directly for the end conclusions:
1. for shavings of 0.05 mm and less there is no tear out even without back iron. 
2. the back-iron must be set proportional to the shaving thickness
3. a steeper back iron angle gives less tearout.

I looked in an earlier post at the Howal Universal Plane, the back iron has a minimal set compared to the Howal values between 1 and 0.3 mm for the back iron setup.  I have also seen descriptions of jack planes favoring a back iron set at 2 mm.  Here the Howal description, that I dated back to the seventies:
1. Schrupphobel  (scrubbing plane):  Use the rounded blade and open the mouth
2. Schlichthobel (jack): Mouth to 2mm
3. Doppelhobel (double iron jack): back iron at 1mm, mouth at 1.5mm
4. Putzhobel (smoother): back iron at 0.5mm, mouth 1mm
5. Reformputzhobel (high angle smoother): back iron at 0.3mm, mouth at 0.5mm and raise the bedding to 49°

What I missed in the Kato and Kawai video was one more test,  they tested on shavings of 0.05 mm and 0.1 mm,  I wanted a test on 0.2 mm shavings.  Just to see how in their setup the ideal distance for a back iron relates to the thickness of a shaving.  But they do mention it in their end conclusion 2. talking of a distance proportional to the thickness.  At first sight Howal also proposes a linear increase with the thickness.  I have read people favoring a nearly static setup as opposed to this linear setup: "1/64 ( 0.4 mm) is at the outer edge of what will actually reduce tearout" I see this as a static setup as Kato and Kawai conclusion 1. sets 1/128 at the inner edge. So setting the back iron close to 1/128 (0.2 mm) would be the only useful position. That idea probably works, but is rather strange as the back iron would protrude under the sole for thicker shavings making it a giant scraper.


I talk about their setup as it misses a mouth. This gives a tightly rolled shaving.  That's different from normal planes where the shaving would come in contact with the mouth that redirects the shaving backwards,  as if confronted with alternating irons. So conclusion 3. is not necessarily the whole story as there are alternatives to a high angle on the back iron to increase the downward pressure on the shaving.  A mouthed plane a well set back iron can give a tell-tale straight shaving.  But any irregularity in this shaving chimney will ask for a lessened back iron position.

My conclusion,  very watchable (... maybe not with the family) video.  And by lack of bevel up planes, more or less setting up a back iron is part of the fun.


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