Plane theory (planing)

[Dan Barr]

I'm sitting here thinking; and it occurs to me that planing is not really that.

let me explain

the sole of a plane is flat. as the blade removes a shaving the toe and the heel of the sole are left to rest on a surface that is no longer flat. the surface under the front, at the mouth is still the original height, but, the surface under the rear portion is lower (by the amount of stock removed).

therefore, the length of the sole of the plane cannot, in theory, be resting flat on the surface of the stock. (both the original height and the new reduced height) the results in my mind are multiple.

As the cut is made, the front of the plane can be kept flat with the pre-existing surface (at original height) by bearing down on the front of the plane. in theory, the rear of the plane will remain elevated above the stock by the amount removed for the duration of the cut. yes, elevated off of the surface completely.

Or

as the cut is made, the rear of the plane is brought down (slightly) and now the front of the plane rises up slightly with the arris (edge) of the mouth being the first point to contact the stock. the blade being the next point of contact and the very tip of the heel being the last point of contact. thus, rendering the sole mostly not in contact with the stock for the majority of the work.

other factors:

cutting a shaving just a few thousandths of an inch (~ .001 - .005) might allow the plane to flex slightly, rendering the sole more useful

cutting a larger shaving would seem to magnify the problem

the length of the sole would increase or decrease the noticed effect. (longer sole = decreased effect and vice versa)


Now, i dont notice this effect in actual use.


Here are my questions.

can anyone explain this theory vs. practice?

in depth...

pre-mature wear on the mouth... (if tilting the plane to the rear after beginning the cut)

unintended differences in depth of cut depending on technique...

anyone out there ever thought of taking off some of the material on the front of the sole? maybe a few thousandths or a general measured amount typically shaved off by that type/particular plane? this would only work on the edge jointing scenario. "riding the rails" as mentioned by tom would negate this tactic on wide surfaces unless you went to the trouble of making a specialized surface on the rear of the sole.

etc. etc.



Thanks,

dan

[Tom Winship]

I understand what you are saying, however, the sole of the plane is wider than the blade, meaning the sole rides on a narrow ridge on each side of the blade. This is if the plane if pushed perfectly straight (no skew). If the plane is slightly skewed (as it normally is), then the sole and heel are riding well outside the path of the blade and the removed mateial.

[Dan Barr]

what about edge jointing. that is the idea in my mind. (stock narrower than the blade)

i do understand what you are saying and that adds another element to this.

thanks,

dan

[Joel Goodman]

I understand what you are saying, however, the sole of the plane is wider than the blade, meaning the sole rides on a narrow ridge on each side of the blade. This is if the plane if pushed perfectly straight (no skew). If the plane is slightly skewed (as it normally is), then the sole and heel are riding well outside the path of the blade and the removed mateial.

Are you saying that the blade is captured by the wood that it's cutting so essentially the plane is resting on the sole while it planing? That does make sense. I'm not sure the metal (or wood) to the sides of the blade come into play much -- after a shoulder or rabbet plane works. It's amazing how hard it is to conceptualize something as old and basic as a plane. A powered jointer is a lot easier to understand!

[Mike Henderson]

For edge jointing it would seem that it wouldn't matter how you used the plane since you'll adjust the blade to get the kind of cut you want.

So if you hold the front down, you'll adjust for that. If you push the back down, you'll adjust for that. Either way, the plane will do what it's supposed to do.

Mike

[Tom Winship]

I agree with Mike. If you are edge jointing and removing as much as .005", considering the length in front and behind the blade, you probably would never know the difference. With .002" it would even matter less.
Of course, I'm one who has to "rock" a chisel several times on the sharpening stone to know I have it resting on the bevel.
Tom

[Frederick Rowe]

Dan - I've also pondered this seemingly contradictory set of facts. It seems clear that the hand plane should have two co-planer soles, the sole aft of the cutter level with the cutter. The fore sole set higher by the depth of the desired cut. The identical arrangement as the powered planer.

It seems with the hand plane's soles in the same plane - and only the cutter projecting, that - as you pointed out - the sole of the plane is never fully flat on the surface after the cutter is engaged. I picture it as the plane sole almost pivoting (depending on whether there is equal pressure on he handle and tote) on the cutter area. Granted, only thousandths of an inch, but not flat with the surface of wood being planed.

In his 4/2009 Blog entry, Christopher Schwarz addressed this somewhat in his entry on edge jointing.


What you have to understand about handplanes is that the tool's cutter sticks out below the sole of the tool. As a result, the tool takes a slightly heavier cut at the beginning of the pass when only part of the plane is on the edge.

Last week I tried to measure this by edge jointing a 30"-long board and then measuring the shaving's thickness at five points along its length. At the beginning of the cut (toe engaged only) my cuts were consistently .0055" thick. In the middle and end of the cut the shaving was .005" thick.

That is not much difference. But it can add up. After several strokes the edge develops a gentle curve to it.Mr. Schwarz doesn't offer an explanation to the difference in shaving thickness at the end of the cut, other than to say it is because the cutter protrudes below the sole.

In the instance of edge jointing, I submit that in theory if the relative angle of the sole remains constant, the shaving's thickness will remain constant. If the angle changes during the cut (as the result of a change in pressure favoring either the tote or handle) the thickness of the shaving will change. I'm at a loss to explain why Mr. Schwarz' results were consistently thinner at the end, other than some slight bias was introduced to the plane during the course of his cut.

[Jamie Buxton]

I've wondered the same thing.

In the case of a power jointer, the knives are adjusted to be exactly in line with the outfeed table. The infeed table is adjusted to be exactly parallel to the outfeed, but lower by the depth of cut. That all seems quite understandable. If you misadjust the knives so that they're above the outfeed table, you produce jointed boards that have concave edges. If you adjust the knives below the outfeed table, you produce jointed boards that have convex edges. (This isn't just theory. I've made both mistakes, and seen the consquences.)

By analogy from the power jointer case, a standard handplane should produce a surface that is convex. I can't say that I've seen this effect. But like you I've wondered what is really going on in hand planing.

[Pedro Reyes]

I think this practice vs theory can be attributed to several things but mostly to the fact that neither the plane nor the wood are perfectly rigid boides.

Perhaps one of those superslow motion close up videos would show how in fact the plane and the wood are angled with respect to each other and that even though apparently both bodies remain in contact only a few spots actually touch, with others being incredibly close to each other.

And then what?

machining the front of the sole by the depth of cut would make a plane funny to start in the middle of a board, sort of like putting a board in the middle of a planer (something I have never done, actually I have never used a planer).

just my $0.02

/p

[Randy Klein]

Yes, no, who cares; it does what it does. It's still up to the user to make things right.

Of course, your theory assumes that you have a perfectly flat piece of wood to begin with. Otherwise the geometry of the wood is more dominant than the planar-ness of the cut.

[Joel Goodman]

I've wondered the same thing.

In the case of a power jointer, the knives are adjusted to be exactly in line with the outfeed table. The infeed table is adjusted to be exactly parallel to the outfeed, but lower by the depth of cut. That all seems quite understandable. If you misadjust the knives so that they're above the outfeed table, you produce jointed boards that have concave edges. If you adjust the knives below the outfeed table, you produce jointed boards that have convex edges. (This isn't just theory. I've made both mistakes, and seen the consquences.)

By analogy from the power jointer case, a standard handplane should produce a surface that is convex. I can't say that I've seen this effect. But like you I've wondered what is really going on in hand planing.

Interesting -- I've noticed a tendency when jointing to produce a convex surface and often take extra shavings in the middle and then plane until I have a full length shaving. I always thought my technique was at fault -- perhaps some of that effect is inherent in the geometry of the hand plane. Anyone else notice this or is it just my inexperience and bad technique?

[Randy Klein]

Interesting -- I've noticed a tendency when jointing to produce a convex surface and often take extra shavings in the middle and then plane until I have a full length shaving. I always thought my technique was at fault -- perhaps some of that effect is inherent in the geometry of the hand plane. Anyone else notice this or is it just my inexperience and bad technique?

Well, that's actually a really good technique to use and one I do on every board, both the face and the edges. David Charlesworth calls it stopped shavings, followed by through shavings.

[Jim Koepke]

This makes me think of a quote commonly attributed to aeronautical engineers, "according to all the laws of aeronautical physics, a bumble bee is unable to fly. No one has figured out how to break it to the bumble bee."

If a plane were taking off as much as 1/64" there could be some sole wobbles taking place. I am not sure how much the wood swells behind the blade after a shaving is made, but if there is not a bevel more acute than the bed angle on the blade, it is going to skid over the wood, not cut it.

Anyone who has had a plane with a wavy, convex or concave sole and then lapped it flat knows the difference a flat sole makes. Surely, the force of a blade cutting into the wood can cause some flexing. One block plane of mine had a convex sole that could not cut worth a darn until the sole was lapped. It also flexed before being lapped. It likely flexed after lapping, just in a manner that rendered better results.

jim

[Leigh Betsch]

Just as I thought. It's physically impossible to get a plane to work right.

[Keith Christopher]

I would think it works because the blade is protruding below the toe of the plane and is going to trim a portion of wood lowering the surface, while the toe and blade remain on the same plane. the area directly behind the blade to the heel will be lower, riding on the new surface X (.005 in the example) below the toe and cutting edge. with the tote being on the back of the plane the natural motion will push the heel of the plane downward riding on this surface. As you reach the end of the cut you release pressure on the knob and glide the plane off the piece sliding completely on the rear of the plane.

I would think beginning shavings are slightly thicker because the plane is not held level at the entry point due to the short surface (balance) area of the toe compared to the sole from just behind the blade to the heel.

[David Gendron]

What about japanese planes that have a hollow in between the toe and the mouth and in between the back of the mouth and the heel?? How does that work? One thing I know for sure is if you want to take realy fine shavings you must have the front of the mouth in contact with the wood!

[Jeff Willard]

Methinks this is an over analysis of a non-existent prollem :D.

[James Taglienti]

http://www.freepatentsonline.com/0502906.pdf

Here you go. The iron ones look even groovier

[Tom Adger]

Dan, you may be doing too much of what you said you were doing in your first sentence.

[Richard Magbanua]

Maybe your thinking relies on the assumption that wood is a constantly rigid and flat surface like metal. In contrast to a flat metal or glass surface, wood is not flat. it also springs back just after the blade's edge passes over it, requiring a relief angle in the design of the plane blade.

As far as making the planes sole higher before the blade by the thickness of the cut it may sound good in theory but you'd have to have a different plane for each depth of shaving you wanted to take. Or, you can have one able to be set to the depth of that particular cut for the finish you want. Which, unlike metal, can vary according to the type of wood, moisture, grain direction, etc.

The other thing to consider is that despite your best efforts, the wood will not become truly flat over the length of the piece. This really isn't the goal anyway. Such a goal would drive you to insanity I would think, especially for a hand tool user. You want to create relative flatness and allow for future wood movement. The more important factors for that would be quality of stock and design of joinery etc. Besides, some think hand tools should leave their mark. The marks of a hand plane can be very nice, esp. to the trained eye such as ours.

This is one of the great reasons why hand tools has opened my eyes. When I used only power tools, I was so overly concerned with everything being adjusted to the Nth degree and now I don't worry too much about that. Kind of liberating.

[Bob Strawn]

Typically I skew my whole plane when I am working a board. This means the two level effect cause by planing is ignored because the functional shoulder is often twice as wide as the functional width of the blade.

Longer planes will tend to reduce the angular change quite a bit. Only when making thick shavings will the two step change be very noticeable anyway.

If you are using a rabbet, which has no functional shoulder, then the lowered back end will make a possible difference in the planes plane angle. This may explain some of the instability and chatter common to rabbets.

A skew rabbet has a shoulder on one side, so it might be more stable when the surface is wide enough for the shoulder to make contact. A skew rabbet tends to pull into the corner, so it is also guided by a second plane that tends to remain stable.

If I am stuck in a corner, then I tend to use a skew rabbet, despite having several more typical rabbets. I find that a skew cut has much less chatter, and the blade lasts much longer when used on knotty juniper.

Since I like to use a Japanese Skew Rabbet, analysis may be a bit more difficult. The Japanese Skew, by design and careful bottom scraping, allows a certain amount of 'English' to be applied. When a shaving is .003" or less, and the plane is 4" or more, then the angular change is quite small when compared to the flex, angle and pressure variations that the user can apply.

Bob

[Jim Koepke]

http://www.freepatentsonline.com/0502906.pdf

Here you go. The iron ones look even groovier

Makes me think of another old axiom, "Just because it is patented doesn't mean it is good for anything or works."

jim

[Jim Koepke]

When a person is planing wood there are a lot of things taking place.

Some of these can be explained by the science of physics.

The rest remains in the realms of skill, craft, artistry and the person using the tool.

If a plane worked perfectly the very first time one took to squaring an edge, that person might be thought of as gifted. Most of us struggled, some more than others. Over time, our bodies have made adjustments. Some have become able to just naturally feel if the edge is square and true.

So, my conclusion is that what can not be explained by the physics of the wood and metal involved must be due to the skill of the artisan using the tool.

jim

[John Coloccia]

When I'm planing, especially edge jointing, I'll typically plane a gentle, concave curve in the piece. Then I'll finish it off by planing the full length. When I've taken a full length shaving, I'm nearly always dead straight. I can't get to straight without doing this, probably because of all the reasons listed above and my own lack of skill.

[Leigh Betsch]

I'd be surprised if some egghead hasn't applied for a National Science Foundation grant to study this. There is probably some tax subsidized research project going on right now at a cost of a half a billion dollars to figure out if wood can be planed. Probably a couple of PHD dissertations in the works right now.:rolleyes:

[Allan Froehlich]

I understand what Dan Barr is saying because I pondered the same question some time ago.

One aspect to keep in mind is that wood is somewhat soft and it changes shape under the weight of the plane. Theoretically, it would be possible to remove some of the wood if the tip of the blade was set exactly to the bottom of the plane. This would be due to the wood raising in the opening of the plane. You would not get shavings from this, just fuzz.

[Danny Burns]

If you have use of a really good micrometer, then try looking at things from the POV of the shaving.

Take one long continuous shaving, and then measure it's thickness at regular intervals.
Then try to check the shaving at the point that your plane shifts into the 'wheelie' state.
Also try a short plane, and then a long one.

I think you will find that looking at different thicknesses of shavings might be interesting, as the plane angle changes more.
If you made a hand-plane like a jointer bed with 2 different heights, then you would be locked into a certain shaving thickness better than others, and some, that are thinner than the bed differences, would not work at all.

[Jim Koepke]

I understand what Dan Barr is saying because I pondered the same question some time ago.

One aspect to keep in mind is that wood is somewhat soft and it changes shape under the weight of the plane. Theoretically, it would be possible to remove some of the wood if the tip of the blade was set exactly to the bottom of the plane. This would be due to the wood raising in the opening of the plane. You would not get shavings from this, just fuzz.

This makes for interesting images in the imagination. The plane's sole is ever so slightly deforming the wood's surface. As it swells back to its original shape, the blade is sheering the "hump" which causes the blade to also lift the wood a little. (think about tear out)

Another image comes to mind that many of us have experienced. It may relate to this. Most of us have probably experienced cutting grass with a flat deck style mower. If the grass is too long, the front of the mower pushes it over and holds it down so the blade never touches it. Think of the front of the mower as the mouth of a plane. The mouth needs to be opened up or in this case, the front of the mower has to be raised above the grass and weeds being mowed. They are definitely two different tools, but they do share the commonality of shearing action.

jim

[Bob Strawn]

I understand what Dan Barr is saying because I pondered the same question some time ago.


When I was first tuning planes I worried quite abit about just this problem. I glued a shim to the heel of a plane just to see if I could fix the problems I was encountering while planing. The shim did not help at all.

In retrospect, the plainsawn, knotty wood I was working with at the time was not going to be easy to work with. Some wood was meant for high angle planes and scrapers.

Bob

[Dan Barr]

does anyone actually know the consequences of this? any data on how this impacts planing?

maybe there is a study, given grants, with numerous plane scientists? LOL

The article mentioned in FWW or whatever seems the only examination of the phenomenon. anything else out there?

maybe an adjustable plane with height adjustments so that the toe can ride by depth of cut higher than heel. ???

i think this would call for a V shaped heel. with the point being at the end of the heel. the V being narrower than the width of cut by 1/8" or so. this could compensate for panel planing and jointing.

call me crazy.

i know... i can get great results without this. just throwing the idea out there.

cheers,

dan

[Jim Koepke]

Because of my intention to sell off a Stanley #75, I was looking at Blood & Gore. It seems this plane is purposely made with a step between the nose and the heel.

jim

[Dan Barr]

can you describe this "step"?

is it the same as what were alluding to in this thread?

cheers,

dan

[Jim Koepke]

can you describe this "step"?

is it the same as what were alluding to in this thread?

cheers,

dan

Alas, the sole on my #75 has been lapped.

Check Patrick Leach's site and read what he says > http://www.supertool.com/StanleyBG/stan10.htm#num75 <

jim