How flat can you plane your work? With a flat plane?

[ivan]

There was some mention of this in a related thread on flattening plane soles, where someone mentioned that a plane will flatten wood only until toe, cutting edge, and heel are just touching. In short, producing a shallow curve through these three points. This is sometimes shown as a diagram in text books. However, I believe this is wrong.

Why? well consider the process of taking stop shavings*, also often quoted as a good way to ensure a flat surface. This makes the surface very slightly hollow (2 or 3 thou or so) to allow subsequent use of a square with no possibility of it rocking.

You keep taking stop shavings until the plane does not cut - nothing coming out of the mouth. It is at this point you have produced the slight hollow as defined in paragraph one above. You have planed a hollow of a shaving's thickness over the length of the plane (or 2 shavings thickenss over twice the length etc.)

Then you take full passes (ie. over the full length of the timber) until you get a continous, full length shaving. At this point the surface should be still slightly hollow, but less hollow than as described in paragraph one above.

The effect of a convex sole will be to increase the depth of the hollow produced by this process by roughly the amount of the convexity. A hollow, concave sole reqires the iron to be set further out before it cuts full shaving, and the above process may produce a convex surface, which you don't want.

At this point we'd better consider the bending of the sole under planing action. My Record No.8 will deflect** between 1 and 2 thou under firm downward planing pressure, and my Clifton 6 about 1 thou. In practice a well set plane requires little pressure to maintain a cut, and a firm downward load is only applied as the toe leaves the end of the board. However, the possibility of sole flexing suggests a slight hollow in the length may be less of a problem in a try plane.

From this you can see roughly how flat a plane's sole needs to be. Your best smoother, probably as flat as you can*** if you like a planed (no sanding) finish, and your try plane not more than a thou or so hollow.

It looks to me as if the old addage of para. 1 is only half the story; maybe the rest (if my thoughts are correct!) got lost in the rapid decline in handwork as working wood became industrialised.

* Stop shavings: start and finish planing about 1 cm from the edge of the work to introduce a hollow over the length. Repeat this till plane stops cutting. Now take full length shavings until you get a continuous ribbon from edge to edge; then stop.
** plane resting on mouth and heel, measured by clock gauge about half way in between, with load on the tote.
*** wet/dry or lapping film on cheap granite surface plate.

 

[Paul Chapman]

At this point we'd better consider the bending of the sole under planing action. My Record No.8 will deflect** between 1 and 2 thou under firm downward planing pressure, and my Clifton 6 about 1 thou.

I'm always rather amused about all this talk of planes flexing. While it has been shown that they can flex with enough pressure, do you really lean on your planes that hard while planing :? If you need to, it's probably time to sharpen your blade :-k

Cheers :wink:

Paul

 

[woodbloke]

..flatten wood only until toe, cutting edge, and heel are just touching. In short, producing a shallow curve through these three points

A plane sole should touch in three points, not two as described. Toe, immediately in front of the cutter and at the heel, but that aside if I worried about the absolute flatness (or not) of a bit of wood I'd never get anything made. As long as the timber can be prepared to my requirements so that I can make stuff, I'm happy Whether it's flat to within a gnats dooberie is purely academic - Rob

 

[xy mosian]

woodbloke - Rob, I agree entirely. Is it fit for purpose? This is my own over-riding test.

xy

 

[David C]

Well,
Ivan's post almost exactly describes the technique which I demonstrate in my second DVD, for flattening a component which is roughly the same order of magnitude of length as the plane.

I will be talking about this and demonstrating "precision planing" at Westonbirt. Courtesy of Mike Hancock.

Slightly convex soled planes (in the length) work fine but significantly hollow planes do not.

We had two current Stanley No. 5 planes in the workshop this summer and they were both about 6 thou" hollow in length. With a two or three thou" shaving set, neither was capable of planing a straight edge.

best wishes,
David Charlesworth

 

[woodbloke]

We had two current Stanley No. 5 planes in the workshop this summer and they were both about 6 thou" hollow in length. With a two or three thou" shaving set, neither was capable of planing a straight edge.

best wishes,
David Charlesworth

Back in the 70's I saw a Record No5 that was about 1 or 2mm concave...and it wouldn't take any sort of shaving - Rob

 

[Caruso]

Back in the 70's I saw a Record No5 that was about 1 or 2mm concave...and it wouldn't take any sort of shaving - Rob

I would call that a compass plane.

 

[bugbear]

There was some mention of this in a related thread on flattening plane soles, where someone mentioned that a plane will flatten wood only until toe, cutting edge, and heel are just touching. In short, producing a shallow curve through these three points. This is sometimes shown as a diagram in text books. However, I believe this is wrong.

It's the most concave surface a plane can make.

A plane can work a remarkably convex surface (and beginners often do...)

Further, working in "japanese smoother" mode (i.e. simply taking a uniform thickness shaving all the way), a plane will obviously maintain a flat surface.

BugBea

 

[ivan]

I don't think flexing is important either; I just put it in because someone raised it on another thread. It took less than a couple of minutes to put a clock gauge on my No8, and see that it did give as described. The downward pressure I used was about what you'd use on the tote at the end of a stroke as the toe leaves the work; not very significant. (If you were to press Very Hard All The Time, you'd just reduce the effective length of the plane)

Stop shavings are a very very old technique, but I have not seen the link between them and the incorrect ,oft repeated addage, that a plane aways cuts hollow, mentioned anywhere else. As Bugbear says, it's the most concave surface that plane can give you. This has the advantage of repeatability, so the technique gives you consistent results at the bench. If it doesn't work, you can also estimate what and how much tuning up you have to do!

Woodbloke, I believe you may be missing the point. It's when the plane stops cutting that toe, cutting edge and heel are just touching. And a plane sole is flat enough if you can use the stop shaving technique and end up with the work a couple of thou hollow. It's the wood wot gives the answer!

 

[woodbloke]

It's when the plane stops cutting that toe, cutting edge and heel are just touching.

Ah...I see your drift now. Agreed - Rob

 

[David C]

My experience is that if one starts with a straight edge, it will become more and more convex as one takes repeated through shavings. The more shavings taken, the worse the convexity becomes.

I would be very interested to hear from anyone who is prepared to try this simple experiment. My results are based on an edge about 15 to 20 inches long, using a No. 5, 5 1/2, or 6.

If two edges are prepared the need for an accurate straight edge can be avoided.

Planes do not maintain flatness. We always have to work with "stop" shavings to preserve it.

This is in stark contrast to a well set machine planer, which can maintain flatness.

Best wishes,
David Charlesworth

 

[xy mosian]

I am reading this thread with a great deal of interest.

Mr. Charlesworth, you have reminded me of a niggling thought. That is as everyone knows. The effective plane sole before the cutter is not co-planar with the effective plane sole behind the cutter on a planing machine. I have been trying to find a scruffy old plane to achieve the same effect on a hand plane. In use I would set the cutting edge of the plane flush with the rear bed.
Now I do not mind the hand work in removing some of the sole but doubt that I can do this with any great degree of accuaraccy.
I can imagine a hand plane with an adjustable sole. Of course it would have to be in the form of a rebate plane to avoid problems. In fact a hand electric plane with a fixed blade and quieter having no motor.

xy

 

[bugbear]

I am reading this thread with a great deal of interest.

Mr. Charlesworth, you have reminded me of a niggling thought. That is as everyone knows. The effective plane sole before the cutter is not co-planar with the effective plane sole behind the cutter on a planing machine. I have been trying to find a scruffy old plane to achieve the same effect on a hand plane. In use I would set the cutting edge of the plane flush with the rear bed.
Now I do not mind the hand work in removing some of the sole but doubt that I can do this with any great degree of accuaraccy.
I can imagine a hand plane with an adjustable sole. Of course it would have to be in the form of a rebate plane to avoid problems. In fact a hand electric plane with a fixed blade and quieter having no motor.

xy

You would need a different "sole step" for each depth of cut!

BugBear

 

[Paul Chapman]

I have been trying to find a scruffy old plane to achieve the same effect on a hand plane.

People have experimented with this in the past but it's never got anywhere. As BugBear says, you'd need to keep varying the front sole as the depth of cut varied.

Stop shavings are a far easier option - and it works :wink:

Cheers :wink:

Paul

 

[xy mosian]

Good points fellas. Although I was not aware of previous trials, which of course suggests failure. I had got around to thinking that a maximun thickness for a hand driven cut would be not much more than 10 thou, 0.25mm, and that in softwood. That puts my adjustable sole in the bin, it would be very difficult to organise a range of adjustment between 0 and 10 thou.

Right back to sleep for me then.

xy

 

[bugbear]

Good points fellas. Although I was not aware of previous trials, which of course suggests failure.

It suggests no improvement over "normal" planes. I think "failure" is a little strong!

BugBear

 

[ivan]

It's not only beginners who can produce a convex edge! I find it quite hard to start a cut "correctly" with shorter planes, even a 5. You haven't got that much toe to set the level for the first few cms of the cut

Perhaps it's time to think a bit more about Alan Peters technique - use a No 7 for everythng. Perhaps the real old timers used longer planes than we think, like the bloke in the background of the archive film on tv*. For all that, past generations of handtool craftsmen using the stop shavings technique would stop taking through savings when the first or second continous shaving appeared. This sugests they expected their plane to gradually turn slightly concave into unwanted convex.



* using tryplane with lenght of over half his height

 

[xy mosian]

Bugbear, sorry this was shorthand for "Failure to be an improvement", which I assumed was the purpose of the exercise.

xy

 

[Karl]

Perhaps it's time to think a bit more about Alan Peters technique - use a No 7 for everythng. Perhaps the real old timers used longer planes than we think, like the bloke in the background of the archive film on tv*.

* using tryplane with lenght of over half his height

I find longer planes much easier to use than, say, 5 downwards, even on shorter stock (shorter than the length of the plane, that is).

I am in the process of building a long wooden jointer, and originally cut the stock to 36". I have trimmed it down to 30", but now wish that I had left it at its original size and tested the performance of a 36" jointer.

Maybe if this one turns out ok i'll make another :shock:

Cheers

Karl

 

[Paul Chapman]

I have trimmed it down to 30", but now wish that I had left it at its original size

But Karl, it's still longer than Rob's, so you are in the lead in the "Size Matters" stakes :lol:

Cheers :wink:

Paul