Hand Tools

Followup Question from PPA

Bill Tindall, E.Tn.
If the plane bottom is a uniform arc up xxx" in the middle I can imagine the plane would plane an arc on what began as a straight board edge. And if one were to continue planing, for some reason, the arc would grow. But unless doing a plane blade test there is no reason to keep planing beyond getting the fist full length shaving. So we only need to consider this defect as potentially significant.

I once had a plane bottom surface ground. The machinist doing the work did a lot of fixturing to make the bottom rigid before grinding. He either believed or tested that the bottom of a Stanley #5 was sufficiently flexible that stiffening was essential before grinding.

I have been told that planes wear near the blade because the plane bottom is flexible and gets pulled into the wood surface at this point, resulting in more wear. Seems reasonable explanation for wear at this point.

So, what happens if I am planing the edge of a 2' long board with a plane whose bottom is 0.0015" up in the middle in a uniform arc? I can see that the plane will have a tendency to plane an arc. But when the board edge is just shaved end to end, the arc on the board will be no more than 0.0015" convex, and it will be less if the bottom is flexible under the conditions of shaving thickness. So what?

If the above assumptions are reliable, what is the significance to edge planing? The potential significance is edge gluing this board into a panel. I have glued hundreds of panels and never had one fail. I will venture that no one on this Forum has glued as many panels as I have. While I am a novice at planing I am not at panel making. I feel I have ample experience to know what is significant to worry about when it comes to edge straightness.

Edge gluing a 2' long board 0.0015" convex does not present a problem assembling a panel from it. I don't think I could even detect this lack of straightness. Even when gluing 8/4 panels the boards are sufficiently flexible to pull bow out of boards vastly more than a few thousandths of an inch. The glue line will even successfully bridge this sized gap if it was not pulled out. The whole reason Franklin recommends 150 psi clamp pressure is to ensure less than straight boards are pulled into submission and the excess glue is squeezed out.

Why is this discussion worth having? Because woodworking should not be sold as being more difficult than it needs to be. Doing so discourages new comers to woodworking, hand tools, planing, take your choice. I've been there and I was misled.

I remain open minded about the significance of the bow in this plane. So far I have not been shown where it matters for practical woodworking, either because I have yet to understand something I don't know, or its not. Appreciate that 100 Forum observers are off to measure the bow in their planes, more or less reliably. They then may launch into needless and RISKY grinding on them. Been there and done that too. Don't mislead them.

© 1998 - 2017 by Ellis Walentine. All rights reserved.
No parts of this web site may be reproduced in any form or by
any means without the written permission of the publisher.