Hand Tools Archive

Subject:
To completely get rid of the rounding *PIC*
Response To:
Digging in to the issue ()

Winston
In the picture of my blade, the worn area on the back is about .005". Removing that by honing the other side of the blade requires removing a lot of material. Assuming a 30-degree bevel and doing a little trigonometry, to completely remove that area by honing the bevel, that involves removing .005" / 2, which equates to removing about .0025" of material from the bevel side.

Here are some pictures from Kato & Kawai. (Not really important for the purposes here, but the picture on the left is what happens to the blade when the cap iron set very close, the other is with the cap iron set further back.)

The upper side in the photos corresponds to the the upper side of a blade when it's installed in the plane, and the shaving passes over it. In a bevel-down plane, that's the back of the blade, and the other (lower) side is the bevel.

Now, if you only remove material from the bevel side, this is how much stuff you need to get rid of, in red.

If you remove material from the bevel (lower) and the back (upper), then this is how much material you need to remove.

(Note that you could remove more material from the bevel side, and that would reduce the amount of material that needs to be removed from the back side, if you go far enough.)

In practice, it's much easier to remove material from the bevel side, because it presents much less area to the stone than the back of the blade. But I don't generally remove enough material from the bevel side alone to fully remove the worn area on the back, and that's why there remains the tiny little rounded off portion near the edge. (I know I'm not the only person who has noticed this -- others say they've seen it as well.)

What I'm trying to do is make it faster and easier to completely get rid of the worn edge. Japanese blades are made with a hollow for this reason.

Regarding burrs: I think it's possible, even with a slightly rounded back, to form a burr and remove it, and it helps if you apply extra pressure at the edge. But there are burrs, and there are burrs. It's still possible to have a burr that you can't see with the naked eye, and can't feel with your fingers, but which will still have an effect on the planed result. And even if you are able to completely remove a burr, it's still nice to make that process faster.

(I realize that all this may not be of too much interest to members of Practical Planers Anonymous, but I find it worth exploring.)

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