Spring Marked Planes:An Addendum

by Herbert P. Kean

From Plane Talk, Vol XIII, no 4 (Winter, 1989)

Published by Astragal Press ©1989
and reprinted here by the kind permission of the author and publisher.


In my article "Spring Marked Planes" (PLANE TALK 1988, No.2), I asked the reader to check over their planes in an effort to come up with an additional information about spring marks. With the responses I received, I was able to piece together more of the puzzle of this intriguing aspect of planemaking.

Carl Bopp said that when planes and irons were made with standard heights, the advantage of "less material being used" in sprung planes was lost. However, he countered this with the fact that savings in labor on the sprung plane, both in shaping the sole and grinding the iron, was much more significant. In addition, a blade shaped for a sprung plane would last much longer than one used in an unsprung plane: the reason being the much larger regrind area of the former (see Fig.1).

The quote in my original article form Holtzappfel's Mechanical Manipulations and Turnings, Vol.II, 1856, can be expanded to include his mention of another advantage of spring, namely "The spring is also partly determined by the position which is most favourable to the maintanence of the form of the cutter in sharpening it; as the obliquity [*] of the sole of the plane causes the cutter, when advanced through it, also to shift sideways and cause a disagreement between thir figures." I have to admit that originally I had trouble fullying understanding theis quote, but Carl gave me a good enough explanation so I could produce the sketch below.


I still maintain that springing originated in order to elimitate the scraping difficulties with certain blade countours. But, considering how many planes are sprung that could function just as well unsprung, I have to conclude that other considerations motivated the planemakers to continue its use. The list of the advantage of spring is impressive:

  1. Less scraping on certain profiles.
  2. Less labor in removing metal from the blade, when originally shaping its profile.
  3. Less labor in removing wood from the sole, when making the plane.
  4. Maintaining proper contour of the blade after sharpening.
  5. A wider steel area availlable for sharpening, therefore a longer blade life.
  6. More uniform mouth opening.
  7. Easier to hold the plane in the cut.

With the original article and now this addendum, I feel a lot less puzzled by spring marks. How about you?

UNSPRUNG OVOLO
Showing a "sidewise shift" to the profile when the cutter is reground and "advanced through the sole." Also a "disagreement" in the dimension of the fillet after regrinding.
SPRUNG OVOLO
Showing no "sidewise shift" or "disagreement" of contour after sharpening.
Fig.1
[Full Size]


[* Defined as the quality in lines or planes of being neither parallel nor at right angles but inclined to each other; the angle of divergence from parallelism.]


Spring Marked Planes

Special thanks to Gerry Kmack for his help in scanning these pages.


20Apr01
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