Full Chisel Blog

December 24, 2008

Twas The Night Before Christmas…

and all I can think about are hand planes.  All of this came about because of the Coffin Smoother that I recently finished and the second Smoother (after Moxon) that I started.  There are two issues; the first I feel is of great importance and forgive me if I am stating the obvious and the second issue may only be important to me.  The first is sharpening plane blades and the second is the Mass and Center of Gravity of hand planes.

With a bevel up hand plane, the angle of the grind of the bevel would effect the cutting angle of the plane.  The bed (frog) would remain the same and that angle together with the angle of the grind of the blade would result in the cutting angle.  Changes in the grinding angle would change the cutting angle of the plane.  Therefore much more care needs to be given to bevel up plane irons (blades), when grinding and honing.  Being as grinding is done only initially, then honed and with each subsequent honing the angle of the bevel up will change, if only slightly.

If there are many honing episodes between grinds, the performance characteristics of the plane will change with each hone, if just a little.  Sharpening bevel down plane irons therefore given the fixed bed, the grind angle only needs to be enough to clear the wood on the back side of the blade. (The perfect angle being say 30 degrees).

Given that, the number of honing episodes would not effect the cutting angle of the plane in any manner.  I have a hollow plane (or is it a round?) that has been ground, sharpened and honed enough times that the bevel just clears the wood on the back side (next to the bed), probably 45 to 50 degrees.  I thought about a re-grind, but the blade only needed a slight touch up on the stone, a bit of a stropping and it worked just fine.  Another similar plane had a much more shallow angle 30 degrees or so.  Both planes do what they do equally well, so the angle on a bevel on the bevel down plane doesn’t matter as long as it clears the wood.

This doesn’t mean that they would be easier or harder to sharpen or whether the edge last longer but try the old iron with the steep grinds first, before you think you have to grind them to the ‘perfect’ angle.  Looks like people in the past just kept honing and didn’t waste the irons with a lot of grinding.

It just occurred to me that this would only apply to parallel, rather than tapered irons.  Old laid steel/wrought iron plane blades are tapered, much thicker at the cutting end and thinning out considerably towards the end (where one would place the sneck).  Grinding to the perfect angle (30 degrees) to maintain that angle may remove excess metal from the iron.  This would explain why many old irons don’t have that perfect angle but are much greater, perhaps their owners didn’t want to waste the tools or didn’t want to change the cutting angle.

So think about those angles when you are grinding and honing your plane blades, new or old.

The second matter will have to wait.



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