RileyG
Woodcarver who has worn groves in knives from working the wood.

I truly agree with mr Porcaro, but i wish to add some thought on back bevels.
One as many knows back bevels could be used to increase the effective pitch on BD planes to emply them as scraper planes
On the other way and my favorite one is to use back bevels on bevel up miter planes to get a low pitch and clearer cut on end grain surfaces, but be wared, if you have got a 20º bevel and add 5-10º back bevel everybody can guess this is too risky to long life cutting edge and it is stupid to use it with figured and exotics species, so the focus is to create a keen edge balancing the upper and back bevel of the blade and not to forget the wood in our hands.
The key to sharpening success is the pressure my dear buddies

It seems to me that the sharpening angles you are mentioning here would lead to a very fragile edge. Certainly the 20 degree included angle from the top of figure 84, but also with 23 and even 25 degrees I would expect micro-chipping or folding over of the edge (ie. rapid dulling). Can you comment on the durability of these edges?

Yea, I think a back bevel is helpful with bevel-up planes, particularly because it is a faster way to remove the wear bevel on the bottom (“back”) of the blade. That wear bevel is, in my opinion, the chief disadvantage of BU planes.

But, a couple of additional points:

1- The back bevel has to be small enough to be contained in the part of the blade that is extended into the throat. This should be easy though. Otherwise, the support of the blade on its bed, one of the big advantages of BU planes, is compromised.

2- For a 12 degree bed BU plane (which is most of them), a 5 degree back bevel yields a clearance angle of only 7 degrees, which is not much. This may interefere with the plane’s function, and at least will tend to aggravate wear on the back of the blade.

That is one of several reasons why I think most BU planes ought to be bedded at 18-20 degrees, not the usual 12 degrees. Interestingly, Karl Holtey has sells a BU plane at 18 degrees, and the L-N #9 is 20 degrees, and, of course, there are plenty of block planes at 20 degrees.

I really think the reason 12 degrees is usual for block planes is that the 20 degree models aren’t as easy to grip, but that is not an issue with BU smoothers, jacks, etc.

But that’s another can of worms.

Thanks for your post.

Rob