flat soles and straight edges. An Experiment

Re: flat soles and straight edges. An Experiment

Andrew F in Australia


>HI David,

It takes a fair while to get the hang of how to produce a jointed board, as you know.

I learnt when I was face jointing 4 by 2 for a job by hand.

I'd contend that it's rather difficult, but can be done - you've got to start with *no* pressure on the rear tote, and finish with pressure on the rear tote only; an extreme version of the way you hand plane normally. And, this only works with a sharp blade (trade sharp). The second the blade blunts, even slightly, you start to crown the surface you're planing.

Probably worth trying once for yourself just to prove that it can be done.

I'd say the crowning effect has something to do with blade sharpness as well as other variables.

Cheers,

Andrew

(who can't be bothered mucking around with this on a daily basis, and instead joints the two edges to within 95 percent by starting in the middle of the board the way you describe, then finishes by taking a single coarse shaving to avoid any of the pertubations you get with a finely set blade. Works for me -> edges match perfectly.)

As an aside, we are trained to use a No6 for most planework, and it's this size plane that I refer to in the above procedure - I think I touched a smoother about two or three years ago. What is your standard 'bench' plane that you reach for in general day to day use.

Re: flat soles and straight edges. An Experiment

David Charlesworth


>Andrew,

I use 5 1/2, for most work, Alan Peters used a 7.

Recently when refinishing a bench surface I found the L-N 8 made things significantly easier.

I still maintain it can't be done, so please humour me and try the experiment, perfect sharpness was assumed!

best wishes,

David

learned something new this week

VTAndy4


>Hello,

In the editor's note in the current _Popular Woodworking_, Chris Schwarz notes that perhaps the oft-repeated pieces of wisdom should sometimes be abandoned. He quotes Michael Dunbar as saying that the repetition (in print) of some woodworking how-to's has resulting in a "contraction" of the variety of methods that are out there.

So, with that in mind, it's great to hear what David is proposing: it really goes against the grain of standard wisdom, and as I've got several boards to joint this week(end), I'm going to give this a shot.

And I'm going to take it a step further. On Thursday I had the pleasure of visiting a cabinetmaker. This is someone who does one-of-a-kind, modern furniture (professionally). His method could best be described as "blended" -- prepping stock with some very fine machinery and then shaping, and finally, finishing with hand tools. Many of his planes were "shop-made", in the Krenov-style. I pointed to a plane about 17" long and asked if that is what he used to joint boards. He showed me a plane that could not have been longer than 9" and said that he usually used it to joint edges, in addition to the longer plane. He explained that he found it easier to joint the edge concavely (exactly as David proposes) with this shorter plane. I was blown away. I explained how I wanted to build a very long wooden plane for jointing edges, and he said that he couldn't see any reason for long jointers unless you were jointing extremely long boards (over 10').

At home, I'm dimensioning boards entirely by hand, so I'm not about to give up using a long jointer plane for that. However, I am now planning to experiment with shorter planes and increased attention to the concave edge. I'm open to all of this, and I'm having a blast!

-Andy

rank beginner extraordinaire

Re: learned something new this week

Warren in Lancaster, PA


>Hi Andy!

Several times I've seen a post on this forum where a worker has just gotten a nice flat jointer plane and is surprised that his boards aren't nearly so flat. It is very much easier for a skilled person to joint an edge with a smoothing plane, than for a beginner to do so with a plane made for the purpose. In fact it might be easier to learn with a smoothing plane because the problems and their solutions are so much more obvious.

I think that with experience we learn to compensate for our tools with our technique. A person who is getting humped boards will alter his technique before he has jointed a hundred boards and a person who is getting concave boards will alter also. A person who uses wooden planes might consider adjusting the sole in response to how it cuts rather than using a straightedge.

I made my first wooden plane in 1975 and I was surprised how easy it was to plane a flat surface with that plane. I then checked my metal plane for the first time and was really shocked at how much out of flat it was. I had learned to compensate so well that I produced a much flatter surface on the plane I made. Of course the metal plane worked better after the sole was worked on, but it illustrates the value of experience and compensation.

Re: I'm lost, any quick drawings?

arw01


>To illustrate the concept?

I'll admit to putting a starrett to the bottom of all my planes, there is no light before I'm done flattening.

Once in a while I can get a really good 90 on a board for edge jointing, but I normally clamp the two into the vise and plane them concurrently so any error is counter-acted.

I will hollow as your video shows just a tiny amount, and I learned to effectively steer the plane with the cambered iron to straighten out any tilt.

So if I understood the message correctly, I take a 5"x20" board and work on the edge. First make that edge flat and true, then make another 5 through passes and check that with a precision straight edge? I should find that it has a high spot, which in corrected by stop shavings to hollow that edge along the length.

Then 2 more, maybe three through shavings and my bump is gone?

Alan

Re: flat soles and straight edges. An Experiment

Dan in NC


>I've convinced myself that I understand this, so I'll take a stab at a physical picture of how this is happening. If my explanation is faulty, I hope someone will point out how.

Assume a straight edge from a powered jointer. We're removing the ripples produce by the cutterhead.

Visualize the handplane as if it were a powered jointer with the outfeed table at the same level as the infeed, and perform these thought experiments:

1 - Maintain pressure only on the infeed side (the knob) straight through the cut. The edge is planed straight until the moment the end of the edge being planed passes the infeed end of the sole. Now the planed edge is pivoting on two points approaching each other as the cut proceeds. The effective depth of cut increases, producing an elliptical profile between this point and the end of the planed edge.

2 - Maintain the pressure only on the outfeed side (the tote). As the edge proceeds through the cut, the amount removed becomes progressively thinner until the end of the edge passes the end of the outfeed. This produces an edge with the elliptical profile on the other end.

3 - Apply a perfect transition of pressure knob to tote, and the removal of material is an interpolation of the two extremes - a convex edge.

Hope this helps.

Re: flat soles and straight edges. An Experiment

Dave Thompson


>Earlier, I had offered that a concavity in the heel of the plane might be desirable as a compromise to the ideal power jointer setup of with an offset infeed/outfeed support. The reason I had explicitly excluded the toe was due to something I had noticed with a very concave transitional. If the portion of the jointer between the front and blade (toe) is concave, then as the plane exits the end of the board, the plane blade will dive into the boad, contributing to round over on the exit end of the board.

I would think the amount of concavity of the heel should match the depth of the blade.

enjoy,

Dave

put another way

Ian (in Sydney, Australia)


>because the cutting edge of a plane extends below the plane's reference surface (the sole), it's impossible to plane to and match the reference surface. To do so would require that the sole pass across the board parallel to and a few tens-of-thou above the edge you're trying to create.

In practice the plane is balanced on the toe and cutting edge or the cutting edge and heel.

David's technique is to induce a deliberate hollow, using stop shavings, which is then removed to get a get a straight edge.

flat soles and cosmic truth

woodburnbob


>David, a bold assertion. But I think you are more right than wrong.

"I still cannot work out the physics of this unfortunate fact, but suspect that the geometry of a plane sole is not correct for producing straight edges or surfaces. Any ideas please?"

My thought is that the depth of cut has to be deepest at the beginning board edge and the ending board edge...given a perfectly flat sole and a cutting edge below the plane of the sole. At the beginning board edge there's no depth stop contributed by the sole behind the blade. At the ending board end there's no depth stop contributed by the sole ahead of the plane. The iterated effect of tiny but fixed variability results in a pattern...in this case a line that should be straight that paradoxically becomes increasingly curved...a sort of fractal, if you've dabbled in chaos theory.

Anyway, David, I remember reading the following Forrest Addy post a few years ago and thinking it was BS at the time. But it stuck in my mind. I now think it's not BS.

Addy Addy's assertions on WC in 2003

I was thinking again about it this summer when the topic of smoothers came up on WC. I decided to break with habit (hypnotic pursuit of flatness) and re-tuned a few old smoothers and block planes "out of flat"...that is, a flat toe but spoon shaped heel per Mr. Addy. I was alternating between using spotting/metal scraper and handfiles. I was pretty surprised how much better the planes worked even if I let the toe acquire some longitudinal radius. I've taken this up to #5s and still not noticed I'm creating any problem. Granted, this may not be a good idea with jointers.

Besides Bailey-oids and Bedrocks, I've bought quite a few "project" infills and rehabed them over the years. I noticed early on that the soles were consistently slightly convex. I thought it was wear or abrasive "sole flattening" by previous owners...degradations from the original perfect flatness. These were some of the victims I spotted and scraped "flat" over long hours in the basement. I now wonder if I hadn't been a complete moron.

The whole thing makes me smile. Over the years here, and on BP, one of the more hotly debated recurring issues has centered on whether a flat sole is all that important. As best I can tell, both camps, those who argue yes and those who argue no, maintain full armies of combatants lying in slumber simply awaiting a new call to arms.

Did you hear something?

Re: flat soles and cosmic truth

Joe Rogers, Northern Virginia


>This whole thread and the Forrest Addy link should be included in the afticles section. This is a proof on the sprung joint theory in a lesser sense.JR

sprung joint theory

woodburnbob


>My left knee has been killing me since mixing and pouring a bunch of concrete last weekend.

I'd be interested in hearing about what the sprung joint theory is and where it comes from. I've never heard of it before.

Re: flat soles and straight edges. An Experiment

Frank D. in Montreal


>Dave,

Doesn't concavity of the heel have the same effect (of creating a convex surface on a board)? If the heel is slightly concave, the blade will rise slightly when the heel embarks upon a board toward the beginning of the cut, producing a convex surface. When the plane exits the board, any concavity of the heel, will once again cause the plane to dive as the toe comes off the board (the blade will start to lower again), rendering the board convex at the exit too. I guess what I'm saying is that any concavity on the heel (only) or the toe (only) in effect renders the whole sole concave, thus creates a convex surface on a board.

I totally agree with Mr Charlesworth on this. It's hard for me to know what exactly comes from my own experience and what I learned from Mr. Charlesworth since I have been steeped in his books since I became serious about woodworking. I do know that I have a concave jointer with which it is impossible to create a flat board, and one that is slightly convex that I use on a regular basis with success. Stopped shavings followed by one or two full-length passes is the technique that I use the most when planing.

This is why I also think that using sandpaper on glass to flatten a sole is an appropriate technique.

My View of the Physics

MarkBSmith


>David,

First, let me rephrase the issue to see if I understand it. Your contention is that with a perfecly flat sole and a plane iron that projects beneath the sole by a small amount, an fixed thickness of shaving should result. Furthermore, this thickness should be the same no matter how close the end of the board because the geometrical relationship of 2 paralled lines (the board edge and the plane sole) and the plane iron does not change.

I think the part that you are missing involves the force applied by the plane iron. The plane iron, in the act of taking a shaving, exerts a small downward force on the plane due to the angle of the cut and the resistance of the wood to the cut. In other words the whole plane is pulled against the board by the plane iron digging into the wood.

This is why jointers work better than smoother to produce a straight edge. With the long length of sole, the force applied by the plane iron does not result in a large deflection. It's a lot harder to push a 28 inch piece of metal against the board than a 10 inch piece of metal.

At the ends of the board, the resistance to the downward force of the plane iron is reduced by approximately half since a large fraction of the sole is no longer in contact with the board edge. Thus, the plane iron can dig deeper into the wood. In essence, at the ends of the board, the jointer plane is reduced to being a smoother.

I hope this analysis is helpful.

Mark

Re: flat soles and straight edges. An Experiment

Pam Niedermayer - Austin, TX


>I find it interesting that almost all my Japanese planes look like a power jointer turned upside down. None of them are configured with a third coplanar area behind the blade, although some other people report adding this third area. To me it seems the only significant difference is that the blade edge is below the toe level in the hand planes; but I don't know that the power jointer's best setting does not have the knife edges protruding a very small bit above the outfeed table's sole.

Pam

Re: sprung joint theory

thomd [email protected]


>The theary is that if there is more assembly pressure at the outer ends it will be less likely to separate if the boards loose moisture. More to the point, since it is the nature of planes to prepare wood this way, and it uses less clamps to make fast the joints it is not a bad way to go for purely practical reasons.

It's also easy to go from the sprung shape and back out the curve to a fairly straight shape if you want to do a rubbed joint.

Re: Arts and Mysteries

thomd [email protected]


>- I use the power jointer in the exact same way. If I think the edge is curved up I just apply the middle third of the joint until that won't cut anymore, I apply the middlw 2/3rd, and so forth until I have all but the ends not cutting and then I do a full pass.

- The japanese jointer is the main Japanese plane that does have after blade contact, and so it will cut the same way. Polishing planes don't need to cut this way, however if they are set extremely fine they will not take a shaving off a concave surface, this is the advantage of having a shorter sole you can get down in there.

I think the main problem with the texbook vision of how a jointer or plane works, by removing an even parallel slice, is that it only works on boards that are already flat. How do you get from various non-flat conditions, and how do you do it while using the plane as your only reference point and not have to grab a lot of marking tools for checks along the way.

This hollowing technique has always been used. I first came across it in the College of the Redwoods tape, so I suppose they teach it there. It remains largely unknown, and arguments break out when you mention it, I got into a big dustup on another board about it.

Well the dustup is one thing, but I just figured everyone knew.

Re: Curved bottom

thomd [email protected]


>Here is how the curved sole will create a flat surface through hollowing out. Of course in this extreme you wouldn't have any pressure at the mounth, we are only talking about a few thou here the thickness of a shaving.

Re: Arts and Mysteries

Pam Niedermayer - Austin, TX


>The japanese jointer is the main Japanese plane that does have after blade contact, and so it will cut the same way.

Thanks, Thom, I just asked Dave about this on the Hiraide forum. I haven't tried to joint using Japanese planes and don't have any Japanese jointers, nor have I tried to joint using the Japanese smoothers. I simply think it's intersting how the smoother profiles match that of power jointers.

Pam

Huh?

Pam Niedermayer - Austin, TX

Re: A lot of waffle.

thomd [email protected]


>Well they really don't: On the Japanese smoother the outfeed is lower than the blade or infeed height; On a power jointer the outfeed is level with the "cutting height" of the rottary blade and higher than the infeed.

When you set the blades on the power jointer you set them so a board placed on the outfeed will be pulled towards the infeed when the blades are rotated by hand. So the outfeed seems lower than the blade, though not lower than the infeed. But in practice what happens is that the blades cut a waffle pattern on the board, and if everything is perfect the high points on the waffle will equal the outfeed height. It's just that the blades are flickering past the boards, not a solid edge so the high point of the blade arc is the low point of the waffle on the board... One has to think about it for a moment.

Re: Huh?

thomd [email protected]


>DC made some mention of a longi hollow plane bottom creating a flat surface, and this minus the "shaving" is the geometry.

Re: A lot of waffle.

thomd [email protected]


>"Well they really don't: On the Japanese smoother the outfeed is lower than the blade or infeed height; On a power jointer the outfeed is level with the "cutting height" of the rottary blade and higher than the infeed."

This assumes one is looking at both bottom up. It's hard enough to explain without getting twisted...

I see, thanks.

Pam Niedermayer - Austin, TX

Re: A lot of waffle.

Pam Niedermayer - Austin, TX


>On the Japanese smoother the outfeed is lower than the blade or infeed height; On a power jointer the outfeed is level with the "cutting height" of the rottary blade and higher than the infeed.

This is what I said, Thom, except I said it as "same as Japanese planes upside down, except for the blade edge protruding slightly on the Japanese planes."

Pam