Plane soles, why flat?

[Bob Glenn]

Reading the recent "Plane Physics" thread got me to thinking about plane design. We go to great lengths to have our plane soles as flat as can be, however, a powered jointer has the leading table lower than the trailing table which determines the thickness of the cut.

I don't care to experiment with one on my hand planes, but, why wouldn't the same principle apply to a hand plane?

[Prashun Patel]

I thought about this too. I think it has to do with the depth of cut and how they're used in practice.

A stationary jointer is designed to take a few, relatively deep passes over an entire length and width of a board. In this instance, good fore and aft support is required.

A handplane is designed to make bunch of relatively thin, overlapping passes over portions of a board at a time. In this instance, it's better (and easier) for the front and rear parts of the sole to be close to coplanar.

I suspect that when we take the cleanest snick pass with a #7 jointer, the board is not in strict contact with the entire length of the sole at any point in time, but the depth of the pass is so small in comparison to this that it's not a practical problem.

[Sean Hughto]

The sole of a handplane is effectively a jig bridging the points on a board to allow the projecting blade to cut all points down to a single level.

If a powered jointer had coplaner tables and a projecting blade, the cut portion of the board emerging on the outfeed side would be unsupported.

[Bob Glenn]

I think you're probably right about the way the plane rides on the surface of the board, not being in complete contact. Thinking about that, in an exagerated case, only the area in front of the blade, the blade, and the heel of the sole are in contact with the wood. That explains the heavy wear in front of the blade.

Let's say we made a plane with the rear of the sole lower than the front to equal the depth of cut. Theoretically, both front and rear soles would ride on the wood, possibly creating a burnished surface.

[Bob Glenn]

The sole of a handplane is effectively a jig bridging the points on a board to allow the projecting blade to cut all points down to a single level.

If a powered jointer had coplaner tables and a projecting blade, the cut portion of the board emerging on the outfeed side would be unsupported.

So, Sean, by this your saying only two points of the plane are in contact with the wood, plus the blade? Why then do we need a flat sole?

[Sean Hughto]

No, I didn't say two. Think of the sole as a reference surface.

[Sean Hughto]

The 75 is the way your suggest, by the way. As Patrick explains:
#75 Bull nose rabbet plane, 4"L (4 1/8", 1936 on), 1"W (1 1/16", 1936 on), 5/8lbs, 1879-1973. http://www.supertool.com/StanleyBG/75.jpgThis is a cheap, little rabbet plane, that is very useful in the shop. It has a top section that arches forward of the blade to form the front portion of the sole. This section is adjustable, forward and backward, to regulate its mouth. This is done by means of a simple screw, which is threaded to lower section, the rear portion of the sole, of the plane. A washer sits under the screw, with the earlier examples having a brass washer. The plane does not have its number cast into it. The lower portion of the plane's sides is machined, with the rest above the machined area japanned.
The lever cap has a thumb screw to hold it and the iron in place (earlier examples will have a slotted screw). There are two lugs cast into the top section under which the lever cap fits. Sometimes the lever cap is snapped and repaired. The plane can choke easily since the lever cap serves as the chip breaker and it sits well back from the cutting edge. Despite the tendency to choke, the plane is useful for trimming and odd rabbeting. I found it very useful when cleaning up years of grunge and paint within the window frames of double hung sash.
The section of the sole ahead of the iron is not co-planar with the sole behind the iron. The plane is purposely made this way to assist it with its cut (you guys what owns the 'lectrical jointahs should know why the plane's sole is the way it is) so there's no need to practice sole lapping on it.

[Andrew Pitonyak]

If a hand plane were setup the way your jointer is setup, then you would probably have the blade level with the rear of the plane. You can then argue if the front of the plane would go up or the rear would go down. One disadvantage is that you would not be able to start a cut in the middle of a board with a hand plane.

[Malcolm Schweizer]

Starting a cut in the middle as Andrew just said is one reason. Another is the fore of the sole needs to press down on the chip ahead of the cut to prevent tear-out. Having the nose elevated even a tiny bit would have the same effect as having too large of a mouth. (On the plane, that is!)

[Reinis Kanders]

Sean is spot on, thus the name for the tool.

[Winton Applegate]

Hey Bob,

Have you been having other great ideas?
Did you write them down ?
Do you remember any one offering you, oh I don't know, a brownie ?

Skip ahead to time signature 16:28 or so here (https://www.youtube.com/watch?v=FOdzdfc2Vas).

Come on I'm just fooling around. Don't take that seriously.

[Kees Heiden]

No, plane soles don't need to be flat :D Have a look at the Japanese with their hollowed soles. On some of their planes they only have two points contacting the wood, one point just in front of the mouth is always one of them.

What you really don't want is the sole behind the mouth being higher! So, nothing like an electric jointer. A bulge behind the mouth is always a good sign of inabality to take fine shavings. The higher sole behind the mouth tends to lift the cutter out of the wood and makes the plane behaving digitally: thick shavings or no shaving at all. I guess, if the bulge behind the mouth would be exactly the shaving thickness, then it wouldn't matter. But in a plane, which you use with variable shaving thicknesses depending on the job, that would be very inconvenient.

Planes weren't born in an industrial design shop. They are the result of thousands of years of evolution. Planemakers tend to continue the development based on what came before. There is hardly any science in these things. They just work. But who knows? Design a plane like that Stanley 75 bullnose. Make the edge exactly equal to the rear part of the sole and adjust shaving thickness with height of the front part. Then let us know how it works ;)

[Brian Ashton]

By it's design a blade that protrudes below the bed of the plane will create a concave surface that is proportional to how far the blade protrudes... but, because of the nature of hand planing, as opposed to running a board over a jointer, a relatively flat surface is created. I.e. you can start a plane anywhere along a surface to eliminate any concave or convex portions that arise over the job,which are inevitable.

Also, if a hand plane were designed to have a lower trailing bed it would be very expensive to produce. but would, when set up accurately, would produce a very flat surface. It could also start a cut mid board simply by puting all the weight on the front, but it wouldn't be as flexible in use as a plane with a flat sole. and would be a real buzz kill as it's set up every time you sharpened the blade would be a real pain. Far more work that it would be worth.

[ian maybury]

It's actually a dead interesting subject. If i'm to be honest i have a Makita power planer, but have never had much luck in getting precision out of it.

These tools (set up as they are) are in truth more like a very short and hand held power/machine jointer than a plane. They theoretically cut in the plane of the front part of the sole, but in practice are hard to get accuracy out of because they need to start from the edge of a board with the short front section of the sole/base flat on the surface, and the plane doesn't always end up always accurately aligned in the line of the required cut in the course of this. (no surprise since it's so short, and because the starting surface may not be all that flat or regular) I guess a hand plane set up that way would likely suffer from the same problem?

It seems as though they are basically set up to peel a layer off the edge of an already flat/machined and aligned surface like say a door.

Wonder how one would work if it was set up like hand plane, or why this isn't done? With both sections of the sole in the same plane, and with the rotating cutter projecting a hair? Thought about as an option for fine finishing it'd quickly run into a requirement for camber on the cutters (x 2 or 3), but even without it should make it a very useful tool for hogging material off a fairly large out of flat surface. In that it'd give control back to the operator.

You'd have to make sure it had stopped before putting it down - maybe safety is another reason why they are set up as they are.

Am i missing something? I wonder if anybody has tried setting one up in this way?

[Jim Matthews]

It's important to remember that the two devices work differently.

The rotating blade is also trying to lift the work off the reference surface.
The weight of the material (and user) are all that keep it in contact.

A plane is held to the material by gravity and user input.
That allows the user to bear down and take a (slightly) thicker shaving.

In practice, a plane body uses reaction force (upward) to counter the cutting force (downward)
to generate shear and take off a slice rather than cut through the wood.

Three points need to be in the same plane for a handplane to function -

The frontmost 'toe' the land just before the mouth of the plane and the abaft "heel" of the plane.

We grind or lap cast iron plane bodies flat because that's the easiest way to get these three
points of contact aligned. Remember that if you're having trouble getting the body squared away
that the blade and frog must be attached and 'tensioned' as cast iron can flex.

I have a few wood body planes that have some measure of twist, but still get a clean surface with them.
I think the appeal of cast iron body planes is their stability and solid blade holding mechanisms.

[Pat Barry]

It must be the middle of winter with everyone suffering the effects of cabin fever to even be discussing something like this. Sheeeeeeesh.

[John Coloccia]

I've wondered about plane geometry too, and the conclusion that I came to is that they're flat so that they're not convex, which would lead to wobbling. Japanese planes have practically nothing extending past the rear of the blade. Just how does that work, hmmm? With skill, that's how, just how it works with western planes. Sean has it right. The sole just bridges points, effectively preventing the blade from cutting the low parts of the board, and requiring the blade to cut the high parts. If you think about it, then, there will be an interesting relationship between the length of the sole, the protrusion of the blade, and the best case flatness that is achievable by blindly making passes. I think what ends up happening with most people, though, is we develop a good memory for where the high and low spots are, and we just target those, and then make some cleanup passes with a very light cut. I've never had good luck with relying on the plane's geometry to magically flatten or straighten anything. I always need to think about it.

[David Ragan]

I've wondered about plane geometry too, and the conclusion that I came to is that they're flat so that they're not convex, which would lead to wobbling. Japanese planes have practically nothing extending past the rear of the blade. Just how does that work, hmmm? With skill, that's how, just how it works with western planes. Sean has it right. The sole just bridges points, effectively preventing the blade from cutting the low parts of the board, and requiring the blade to cut the high parts. If you think about it, then, there will be an interesting relationship between the length of the sole, the protrusion of the blade, and the best case flatness that is achievable by blindly making passes. I think what ends up happening with most people, though, is we develop a good memory for where the high and low spots are, and we just target those, and then make some cleanup passes with a very light cut. I've never had good luck with relying on the plane's geometry to magically flatten or straighten anything. I always need to think about it.


Seems to me like, then, you're referring to the length of the sole giving a particular plane it's purpose, right?

The point about Japanese planes having no behind the blade is worth considering (I did not know that), but then, how do they use them like we do our long jointers?

[John Coloccia]

Seems to me like, then, you're referring to the length of the sole giving a particular plane it's purpose, right?

I wasn't thinking in those terms specifically, but that's a consequence. My only point was that planes don't really work by magic, and actually the geometry works against what you're trying to achieve, but we achieve it anyway because people get an intuitive understanding of how things work and just do it without thinking about it. For example, when I'm jointing an edge, I almost always make it slightly concave first, and then do a couple of light cleanup passes to really get it dead straight. That's working WITH the geometry of the plane, as opposed to fighting it. I suspect most people do the same thing, whether they do it consciously or not. That's for Western planes, anyhow. My personal experience with Japanese planes is that they tend to want to make concave surfaces, so I tend to try and take less from the center then from the ends, and everything works out.

[Michael Ray Smith]

Three points need to be in the same plane for a handplane to function -

The frontmost 'toe' the land just before the mouth of the plane and the abaft "heel" of the plane.

We grind or lap cast iron plane bodies flat because that's the easiest way to get these three points of contact aligned.

Thanks, Jim. I've often wondered about the question asked by the OP and in particular wondered if all the work that goes into making a plane sole flat and smooth is a bit misplaced. But I've never really taken the time to try to understand the geometry and dynamics. Your observation that the goal is to make three parts of the sole coplanar makes sense to me, but I'm not sure I understand exactly which three parts you're talking about. By the "frontmost toe" I can imagine why one of the sections should be near the front of the plane, but I don't see the need for it to be right at the toe of the plane. In fact, I've lapped the soles of enough old Stanleys to observe that the toe on most of them was a bit "higher" than the rest of the sole, and I doubt that was just an accident or artifact of manufacturing. I suspect it was intentional to allow the plane to glide up over high spots in the wood, like the runners on a sled. Granted, the distance between the front area of contact and the back area of contact is, in a sense, the "true" length of the sole, and the farther the two are apart, the more the plane will bridge the low spots in the wood rather than following the contours. That's why jointers are long and smoothers are short. Am I thinking correctly so far?

Mike

[Bob Glenn]

Hey Bob,

Have you been having other great ideas?
Did you write them down ?
Do you remember any one offering you, oh I don't know, a brownie ?


Skip ahead to time signature 16:28 or so here (https://www.youtube.com/watch?v=FOdzdfc2Vas).

Come on I'm just fooling around. Don't take that seriously.

Winton, be careful or I'll send the dog army after you! Read the above posts......I'm not the only one pondering the great questions of the universe!

[David Ragan]

I wasn't thinking in those terms specifically, but that's a consequence. My only point was that planes don't really work by magic, and actually the geometry works against what you're trying to achieve, but we achieve it anyway because people get an intuitive understanding of how things work and just do it without thinking about it. For example, when I'm jointing an edge, I almost always make it slightly concave first, and then do a couple of light cleanup passes to really get it dead straight. That's working WITH the geometry of the plane, as opposed to fighting it. I suspect most people do the same thing, whether they do it consciously or not. That's for Western planes, anyhow. My personal experience with Japanese planes is that they tend to want to make concave surfaces, so I tend to try and take less from the center then from the ends, and everything works out.

Well,. hey, on a good day I will realize that I don't know squat.

Recently, I asked for information to clarify the physics of handplanes. On comes the deluge of technical information. I had to cry uncle.

[Steve Rozmiarek]

I'm sure you guys are aware of the Hardt patent planes. His claim to fame was to adjust the depth via adjusting the sole rather than the blade. I don't own one, so I borrowed a photo from Meekers site. $6k will buy the plane, just FYI if anyone wants to review it. This particular example has the conventional depth screw as well, some of the models don't. PTAMPIA shows three models.

http://www.patented-antiques.com/images/2010WRIT/2010Tools/Hardt/MVC-002F.JPG

[Pat Barry]

I'm sure you guys are aware of the Hardt patent planes. His claim to fame was to adjust the depth via adjusting the sole rather than the blade. I don't own one, so I borrowed a photo from Meekers site. $6k will buy the plane, just FYI if anyone wants to review it. This particular example has the conventional depth screw as well, some of the models don't. PTAMPIA shows three models.

http://www.patented-antiques.com/images/2010WRIT/2010Tools/Hardt/MVC-002F.JPG
Is it just me or does that one appear to be set incorrectly?

[Steve Rozmiarek]

Is it just me or does that one appear to be set incorrectly?

Yeah, I'm pretty sure that one won't cut as set. Kind of amusing. Similar to getting a chuckle out of haw many old molding planes you see with the wedge/iron reversed.

[Jim Matthews]

As best as I understand this, we see it the same way.

I heard Jim Tolpin talking about how it was possible to get an entire door flat with a block plane,
and how nobody did that more than once. Longer planes describe a longer arc that the cutting edge could follow.

A short body has the two limits of the plane (the plane sole and the cutter depth) relatively close together.
A long body has the two limits relatively far apart - a 4 thousandths thick shaving is relatively smaller than longer body.

In practice, I don't much like planes longer than 9 inches. Beyond that size, I'm using a jig or shooting board to keep things aligned.

******

You're absolutely right about the relieved front and rear projections on cast iron plane bodies.
I was taught to lightly 'feather' the front and rear half rounds along with the sides to about
2 thousandths and smooth the edge of the casting so as not to mark the work in careless handling.

I'm mostly working with wood body planes these days, so those considerations are less important.