german planes

[bugbear]

Percy Wells and John Hooper in Modern Cabinet Work describe the handiness of having a 'Bismarck' roughing plane in one's kit which by description is clearly a horned scrub plane; there is a line drawing too I believe. If precedence is needed in the British tradition, then, there you have it.

Or it might just be a jack; this Melhuish catalogue caused me to take pause and consider:

post725105.html?hilit=scrub%20textual#p725105

BugBear

The line drawing on the plate on page 8 of the Wells book shows essentially the old Ulmia scrub plane. The horn is the typical one found on ECE and Ulmia planes and not the turned handle of the illustration in Melhuish. They were referring to a German plane.

FWIW, there is a line drawing of a typical English jack plane found on the same plate.

Yes, that's all quite well understood. But the usage in the Melhuish catalogue is quite unexpected.

BugBear

 

[Trafalgar]

Melhuish does say the plane is available with a 'ram's horn' instead of a peg.

Imitation is the sincerest form of flattery I suppose.

Anyway, the British kit has included dedicated scrub planes at points in the past. Too bad Larry Williams doesn't hang out here. He was quite sure that this was never the case. Taken with a grain of salt of course. He doesn't think chipbreakers work either.

 

[Jacob]

In theory the nearer you get to a semi circular trough the faster the rate of removal.

And yet actual evolved-over-time scrubs don't remove semi circles. I think that theory is (at best) unproven. Where did you see it, or did you make it up yourself?

What's the reasoning and/or evidence?

BugBear

Theory is the operative word. In theory the ratio of cross sectional area of removed material to the length of the cutting edge is greatest for a semicircular trough. The shorter the cutting edge the less the effort required. The scrub (and any cambered blade) is towards the semi circle but in practice there are other issues.

 

[bugbear]

Theory is the operative word. In theory the ratio of cross sectional area of removed material to the length of the cutting edge is greatest for a semicircular trough.

Well, that's true. It's not a theory or a hypothesis, it's a arithmetic fact, as far as it goes.

The shorter the cutting edge the less the effort required.

That's certainly not true, at least not without MASSIVE amounts of qulifiying gumph.

The scrub (and any cambered blade) is towards the semi circle but in practice there are other issues.

In any well thought out theory there are other issues, like chip deflection effort and a funny little thing called "grain". Have you noticed that wood isn't homogenous?

Who proposed this silly theory?

BugBear

 

[Jacob]

erewego back to the playground!
No BB, just because you don't understand it, doesn't mean it's silly. You really must try harder.

Consider the following tools for maximum material removal:
turning; roughing out gouge, semi circular.
chopping; adze with deep near semi circular profile
plane; scrub with deep camber verging on the semi circular.
For each of these (depending on the material) there is a maximum size beyond which they are less usable (for max removal) due to the effort required (or power of the lathe).
No doubt other examples could be found.

Conversely for fine finish in all three cases a straight (or straighter) edge.

Think about it BB before you start dismissing it as silly. Or perhaps don't bother, I don't think you will get it.

 

[bugbear]

erewego back to the playground!
No BB, just because you don't understand it, doesn't mean it's silly. You really must try harder.

Consider the following tools for maximum material removal:
turning; roughing out gouge, semi circular.
chopping; adze with deep near semi circular profile
plane; scrub with deep camber verging on the semi circular.
For each of these (depending on the material) there is a maximum size beyond which they are less usable (for max removal) due to the effort required (or power of the lathe).
No doubt other examples could be found.

Conversely for fine finish in all three cases a straight (or straighter) edge.

Think about it BB before you start dismissing it as silly. Or perhaps don't bother, I don't think you will get it.

In the plane case you cited, the notion that the force required is simply proportional to the length of the cutting edge simply doesn't stand up to consideration.

Everybody with a plane knows that despite the blade staying 2" wide, altering the depth of cut has a massive effect on the force required to push it.

Simple, clear, move along, nothing to see here.

(oh, and your last conclusion (maximum size) is quite a separate concept from a semi circle being optimal in some way, is obviously true, and not very relevant to anything)

The leap from "some real world tools don't have straight" and "a semi crcle is optimal" is a leap too far.

And I think I've worked out who proposed this theory.

BugBear

 

[Jacob]

.....
Everybody with a plane knows that despite the blade staying 2" wide, altering the depth of cut has a massive effect on the force required to push it....

Yes.
Except if the blade is cambered the cutting edge doesn't stay 2" wide.
A slight adjustment and it will go from a narrow paring from the centre (easy) to a wide full width paring (more difficult).
If the blade is dead straight it will go from easy when it is taking off just the high points, to difficult when the blade is full width engaged. This is one reason why people have so much difficulty with perfectly straight edges - there isn't an in between, it's all or nothing.
I'm talking about "cutting" here, not "digging" where the blade prizes up and brakes out the shaving, as you might do with a plough plane or an over extended plane of any sort.

 

[bugbear]

.....
Everybody with a plane knows that despite the blade staying 2" wide, altering the depth of cut has a massive effect on the force required to push it....

Yes.
Except if the blade is cambered the cutting edge doesn't stay 2" wide.
A slight adjustment and it will go from a narrow paring from the centre (easy) to a wide full width paring (more difficult).
If the blade is dead straight it will go from easy when it is taking off just the high points, to difficult when the blade is full width engaged. This is one reason why people have so much difficulty with perfectly straight edges - there isn't an in between, it's all or nothing.
I'm talking about "cutting" here, not "digging" where the blade prizes up and brakes out the shaving, as you might do with a plough plane or an over extended plane of any sort.

If we continue to consider the case of a straight blade, and avoid changing the subject to general planing technique, my simple point remains perfectly accurate.

I am happy to cede that I should have stated clearly that I was analysing a straight blade, but I thought that was obvious. Still:

Everybody with a plane (with a straight blade) knows that despite the blade staying 2" wide, altering the depth of cut has a massive effect on the force required to push it.

(e.g. when taking a full length full width shaving of 1/100" changing the depth of cut to be 2/100", or vise versa)

We can have a lovel discussion about the advisability and use of a cambered blade for general planing some other time, in a thread of its own.

I wish to bring the discussion of your theory about semi circles to some kind of conclusion first.

BugBear

 

[Jacob]

You haven't understood anything so far. I suggest you go away and think about it for a few days before replying.

Basically a device which cuts (not levers, digs etc) a semi circular groove will remove most material for a given effort as it has the least material to cut (least length of cutting edge) for the greatest cross section area of waste.
Hence the tools mentioned above.

 

[bugbear]

Basically a device which cuts (not levers, digs etc) a semi circular groove will remove most material for a given effort as it has the least material to cut (least length of cutting edge) for the greatest cross section area of waste.

Yes, the maths of that is simple. If (and only if) the force required is directly (and only) proportional to the length of cut, it follows immediately that a semi circular cut of some size will remove the most material for a given force, in the same way that a fence of a given length will enclose the most land is made into a circle.

So the question falls on the axiom - is the force required to make a cut directly (and only proportional) to the length of cut?

The simple example of changing the depth of a normal bailey plane when taking a normal, full length full width shaving (yes, with a straight blade :roll: ) demonstrates clearly that the force required is in fact also governed by other factors (including at least depth of cut).

Thus the axiom is false, and the theory with it.

BugBear

 

[Jacob]

You are getting closer! Well done BB. :roll:

NB I didn't say it was the only factor.
How do you yourself account for the ease of cut and speed of waste removal of a scrub plane? With a narrow blade (30mm ish) you can do a 1/4" deep cut quite easily. Your adapted no 4 (5?) is probably too wide for this.

 

[Trafalgar]

Good Lord surely there isn't an argument going about whether a dedicated scrub plane with a thick iron and curved blade will remove wood faster and easier than a Stanley/Record/Bailey pattern No. 5 jack plane.

 

[woodbrains]

Hello,

The reason behind the cambered blade of a scrub has little to do with the effort required to push it, so the debate is moot. The width of the plane iron regardless of the profile, is what dictates the effort needed to push it, for a given amount of removed material. The reason the scrub is cambered is because we would not want to plough flat bottomed grooves as we work, but a series of overlappable scoops. A shaving of this type will lift up more readily than a flat bottomed one, since the sides will still be attached in the latter case, for a deep cut, the radiussed used ones are free.

Ideally a scrub should cut right to its edges, or neat enough, or we might just as well use a 25 mm iron. so a plane cutting right to its edge of the iron, whether flat of cambered are to all intents and purposes equal, for such a narrow blade. So arguing about which is easier to push is a bit academic. We might have to think more in terms of volume of wood removed in shaving, which will be hard to calculate in a meaningful way.

 

[Carl P]

On a more practical note, how does this relate to an ideal camber on a scrub? Has anyone tried using a semicircular profile? Would a 'U' shape with a flat bottom be as effective?

Cheerio,

Carl

 

[woodbrains]

On a more practical note, how does this relate to an ideal camber on a scrub? Has anyone tried using a semicircular profile? Would a 'U' shape with a flat bottom be as effective?

Cheerio,

Carl

Probably, the shaving would be released at the edges, so it would work well. I doubt the shape of the scallop would have any advantage over the standard scoop, and the blade would be a little fussier to sharpen, so it is unlikely to be useful.

It is the release of the heavy shavings that makes a scrub efficient, not its ease/difficulty to push. It is for the same reasons roughing gouges, carving gouges, trimming axes, whatever are radiused, any other discussions are incidental.

Mike.

 

[bugbear]

Good Lord surely there isn't an argument going about whether a dedicated scrub plane with a thick iron and curved blade will remove wood faster and easier than a Stanley/Record/Bailey pattern No. 5 jack plane.

Good $DEITY, No!

Scrubs are great.

The "debate" is about a trivial (and invalid IMHO) little piece of mechanical analysis.

BugBear

 

[Jacob]

Hello,

The reason behind the cambered blade of a scrub has little to do with the effort required to push it, so the debate is moot. The width of the plane iron regardless of the profile, is what dictates the effort needed to push it, for a given amount of removed material. ...

Nope. You try scrubbing with narrow rebate plane frinstance. Impossible.
Interesting that so many people go on for years about camber, scrub planes etc without the foggiest idea of how/why they work. Well now you know! :lol: (except it'll take bugbear some time to catch up).

 

[bugbear]

NB I didn't say it was the only factor

You said:

The shorter the cutting edge the less the effort required.

I didn't see any qualification, although plenty is needed, as I've been carefully pointing out.

Since blade length being the only factor affected the force is required for the "semi circle is optimal" theory
to be true, I guess the theory is now dead.

BugBear

 

[woodbrains]

Hello,

The reason behind the cambered blade of a scrub has little to do with the effort required to push it, so the debate is moot. The width of the plane iron regardless of the profile, is what dictates the effort needed to push it, for a given amount of removed material. ...

Nope. You try scrubbing with narrow rebate plane frinstance. Impossible.
Interesting that so many people go on for years about camber, scrub planes etc without the foggiest idea of how/why they work. Well now you know! :lol: (except it'll take bugbear some time to catch up).

Hello,

Jacob, this is what I just said, it is clear you do not understand the points written. The scrub works because it releases the shaving, which is why it was designed like it is, NOT to make it easier to push, a plough of a similar dimension COULD be pushed, but it wouldn't release the shaving. if there is a minuscule and immeasurable advantage in pushing a scrub it is entirely beside the point.

Mike.

 

[Jacob]

...I if there is a minuscule and immeasurable advantage in pushing a scrub it is entirely beside the point.

Mike.

There is a huge advantage in pushing a scrub plane - which is the whole point of using it. It's easy to take out a deep shaving with a scrub, but not with a rebate plane.
Keep thinking about it I'm sure you will get there in the end. Dunno though, maybe you won't!
Anyway I've explained it and I can't be bothered to keep repeating myself so I won't post again in this thread. Cheers!

PS :roll: except to say - yes a scrub plane "releases" the shaving as you term it. But so does a shallow cambered plane. But the scrub plane shaving is fatter - more wood removed for the same effort (AOTBE).