Maybe I'm not too bright, but....

[Hunter Wallace]

So I was grinding my iron for a LN #4 the other day and I
said to myself, "Self, if this iron is bevel down and the
shavings are cut up and over the "back" of the plane iron,
then why, oh why, is there always so much discussion
about the angle??? If the blade is bedded at 45 degrees
then why grind at 25 or 30 degrees? In theory, if you
ground at 40degrees and put a hone on it at another
few degrees then, again in theory, you would have more
material at the blade edge and it should stay sharper longer,
right?"
What does everyone think? Am I missing something here?
And if I am missing something, then what is it?
I understand the principle behind having a specific grind angle
for a blade when used bevel UP, but if the ground/honed
face of the blade in a bevel down application clears the
surface of the wood then wouldn't it make more sense to
keep as much metal at the cutting edge to help reduce wear???
Alright, I just can't wait to hear what you guys have to
offer for advice on THIS one :D

[Steve Clardy]

Sure. I'm interested in the responses too

[Dan Forman]

It's basically a matter of balancing the maximum wear with the keenest edge. If you sharpened a splitting mall up to an 8000 grit waterstone, it would not peel a carrot as well as a similarly sharpened knife, even if the cutting angle were the same. Anyway, that's my story, and I'm sticking to it.

Dan

[Dennis McDonaugh]

Hunter, check out this link.

http://www.sover.net/~nichael/nlc-wood/chapters/caop.html

[Mike Wenzloff]

The short answer is it has to do with fiber spring-back and clearance angles. Add to that, which isn't discussed in the Whelan scans are wear bevels, their rate of growth, shape and, again, clearance angles.

Take care--and have fun!

Mike

[Dan Forman]

I was aware of the clearance angle being one limiting factor, but am I completely off track with the notion that smaller bevel, say about 20*, will have an advantage in taking shavings (though not in durability) over one approaching 45* ? Otherwise, wouldn't we all be sharpening to about 43* ?

It seems that the most common compromise is around 30 to 35*

Dan

[Mark Stutz]

Dan,
I was under that exact impression...that the 30 to 35 deg. angle was mostly a compromise between edge keennes and durability.

[Mike Wenzloff]

20 degrees and it is easy to fracture the cutting edge in a plane with 45 degree or higher bedding.

35 degrees leaves 10 degrees clearance, but I would maintain that edge retention due to the lower wear bevel makes it where one must either hone more frequently or push harder to take a shaving.

And different woods affect the fiber spring back to lesser/great extents.

iI grind at about 25 degrees and add a secondary until it comproses the entire primary bevel and then grind again.

No magic bullet. Another consideration is the wear characteristics of the blades themselves: which kind of steel.

Oh now my head hurts. Making shavings is easier than thining about the dynamics of why it works <g>.

Take care, Mike