The basic theory of bench planes in a nutshell: the longer the plane body, the flatter the surface produced will be. This makes a certain amount of sense. If you have a wavy, curved, or otherwise irregular board and you run a very long bench plane over the wood, the long sole of the plane will rest on any high spot, and all you can do is plane the high spots. The shorter the sole, the fewer high spots you can contact at once, so the plane will start to follow the contour of the wood. Let's say you are making a dining table. A long jointer plane will create accurate edges for joining boards together to make a wide table. Long planes will also ensure that your table is flat, not cupped. But suppose one bit of one board is a touch lower than the rest of the table. Continuing to use a very long plane would necessitate planing down (by hand) the entire table top before you would get to the low point. Shorter planes, "smooth planes," would follow the minor surface irregularities - planing less accurately, but giving you the quality of surface you would need to finish the table top. We're talking minor irregularities, so nobody would notice the lack of uber-flatness anyway. Therefore, using a short plane to clean up those surfaces for visual appearance's sake makes a lot of sense. This is the whole point of a smooth plane. A wooden smooth plane is usually around 7" long and takes over from jointer and panel planes when the surface is flat enough and ready for the clean up before finishing. Cabinet scrapers are essentially planes with a zero sole length; they can follow any surface. Scrapers are good to use after the smooth plane for areas the smooth plane missed.
The smooth plane is especially important when you are in the 17th century and bicycles hadn't been invented for Gilligan to power the generator for running your random orbital power sander and all wood needed to be finished by hand. In modern times wood is typically milled by machine to a high, flat standard so the forgiveness of a short plane is less important. The modern iron Bailey style smooth plane at about 9" long is a little longer than a traditional wood smoother and the sole of both wood and metal versions are flat. Flatness gives you a certain predictability and accuracy in use. A concave sole will never cut a flat plane, but a convex sole will follow small variations in the material and some modern instructions suggest (on a wooden plane) relieving the sole in front and back of the iron. This modification is rare in western planes. We want them flat. However in Japanese woodworking tradition relieving the sole in front and back of the iron is part of their tuning up procedure and why wooden Japanese planes can be made to consistently plane long shaving of absurd thinness. The plane just follows minor variations in the wood and doesn't try to impart accuracy. By the way I am talking about a convexity over the length of the plane's sole, not the width. Typically smooth planes irons in both Western and Eastern tradition are very slightly convex to prevent noticeable ridges at the sides of the cut.
(Smooth planes have other useful applications in the shop, but for now let's focus on their main use).
Question: Why do we not follow the Japanese concept of having a convexity to the sole of a smooth plane.
What do we know about smooth planes from the historic record?
Aside from scant archeological evidence the main source of English woodworking practice is from Joseph Moxon's 1678 "Mechanick Exercises". Aside from brevity and not being a cabinetmaker or carpenter himself, Moxon still has a lot of useful information. Here is what he says about the smooth plane:
This tells us the basics but not much more. Moxon copied his pictures from a French book, André Félibien's "Principes de l'Architecture, de la Sculpture, de la Peinture, &c" (1676) so we can't really be sure if this is the type of plane used in London at the time? England? or whatever. A second 17th century source Randle Holme's "Academy of Armory", published ten years (1688) later starts off with the same picture but seems to have a lot more to say on the issue.
Holme might have gotten his drawing inspiration from Moxon, or from Felibien, or maybe even real life. There are some clues in the text.
Holmes list's the plane, but also mentions that it isn't the same as another smooth plane that he also illustrates later in the book. This plane, he says is of a contrary design to the other, has a flatter bottom, and he hints that the rounding at the ends is a person style of the craftsman. It's the second smooth plane that is more interesting.
First of all the text seems inspired by Moxon. It's not quite a word for word copy (which Holme does in other places in the book) but to me is seems like he thinks that the Moxon style smooth plane is atypical and this rounded up version is a standard style. And, more important he finds it important to mention that the other style is known for it's flat sole, implying that this plane doesn't have a flat sole. Now there are two ways to look at this I think. The first is that as a smooth plane gets shorter it will be more forgiving on surface irregularities but it also becomes much harder to hold it comfortably in two hands. The illustration that Holmes provides suggests that the plane curved up so that it could be longer and easier to hold, but have a fairly small contact area with the wood, giving an effective shorter length. This would make it a more effective smoother. The second way is that the sole of this plane is slightly convex. Unfortunately the text doesn't clarify this, but the implication is that if the other style has a flat sole, this wouldn't. As far as I know no other image of a plane like this exists in print that pre-dates Holme (I could be wrong). So where did he get this image from? Real life experience? That makes sense as his reference to the other flat style plane with the Moxon copied illustration seems to be described as another style, but more craftsman dependent, not usual. By usual I mean usual at least for the planes he saw in his area.
Another important observation that we can make from seeing this alternate smoothing plane is that Moxon and Holme are not definitive guides to early woodworking. What they are are very useful recordings of how two people saw the craft world in their area. Randle Holme (1627–1700) lived in Chester which is on the west coast of England and in the 17th century a world away from London. Travel to London would have been arduous and time consuming. The book, which was probably the largest book printed in Chester up to that time was a huge undertaking. There is no evidence to suggest that either Moxon or Holme did any practical research on woodworking other than have copies of the two other recent titles in the subject. There is no information on how they gathered their material, if they talked to local craftsman only or ventured outside their own areas for different terminology and techniques.
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11/04/2020 Jesse Griggs
Fascinating point in the convex toe-heel smoother. Holmes' picture reminds me of a plane i saw Peter Follansbee use on several episodes of the woodwright's shop. IIRC the pattern was Dutch, and he used it as a scrub plane to hog off material. I've been thinking about making a laminated smoother and will probably try to incorporate those ideas (convex/ longer).