Plane soles, why flat?

[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.

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.

[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.

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.