>Scenario: you cut grass with a sickle. If you move the sickle slowly the grass will just roll over and not be cut. If you swing the sickle the way it is designed for, the grass will get cut cleanly (my first analogy had something to do with samurais, and was a lot more gory :-) ...
Has anyone ever studied this phenomenon with regard to planes? Seems to me that planing with a very fast stroke can lower the occurence of tearout, all other things being equal... Obviously, a light plane will help obtain the fast stroke here...
I was at the Ottawa Wood Show this afternoon, and at the LV booth I had the opportunity of playing with all their planes. One was the low angle block plane with the tote and knob attachments. To me it looked kind of goofy in picture, but in person it looks OK. Anyway, they had a nasty piece of Claro walnut to play with, grain going in all directions, and it had to be attacked from both ends with a high angle blade in the heavy smoother to obtain respectable results.
Some time later I came back to the booth and gave that idea of mine a try. Going with very fast strokes with the souped up block plane, I got results no worse than with the heavy smoother used at a normal speed (with a 37 degree effective angle...). And direction of cut seemed to matter less. Now, that plane setup weighs in the vicinity of two pounds, so that helps a lot...
I can't vouch for the degree of sharpness of each plane blade, I was just using what was there (and so did a lot of people, I'm sure).
>One way of looking at it is that the idea behind the cut is to concentrate as much energy at a single point as is possible. This totality is often refered to in knife circles as "cutting power". Many things go into this but obviously a increase in speed is one of them. Japanese planes are specifically designed this way, according to some sources, and some Japanese carpenters plane with a very quick stroke.
The sticky wicket is that speed can affect your accuracy, causing the plane to loose contact with the surface being planed, of course it's easy to tell when that happens, and all one need do is optimize the results.
People often have unrealistice expectation about how much speed they can control. An example of that was the speed increase required to make a 14 oz titanium framing hammer hit as hard as a 21oz one. Just for fun I once worked that out, and it was the same speed increase required to make the difference between drives hit by a level par golfer, and the leading distance drivers on the PGA tour, at the time. So what seems like a simple task, in this case increasing hammer speed by 22%, may be a very significant increment.
>As Thom says, the speed has to be controllable. In those situations where it's very important to keep contact for a while, say in planing contests and other edge work, I go very slowly. But for shorter work, whether from scrubbing to initial flattening as well as final smoothing on long pieces as well as all work on short pieces, I tend to move the planes very fast. Also as Thom says, Inomoto-san, the master dai maker, says that you're supposed to plane very fast. So I suppose the goal is to also do long work with speed, but I'm not there yet.
>The analogy to grass or heads will not work for wood, unless you do not clamp down the wood you are working on. If you set a piece of wood on the bench loose, and you had to plane it, your planing speed would have to be very fast so the board is planed before developing inertia from the applied force and started moving in the same direction as the blade. This is what happens to grass being cut. Normally, a board is clamped to the bench, and the wood fibers are effectively held in position while being planed because they are surrounded by other fibers.
>I remember an excerpt from "the workbench book" by scott landis where Toshio was trying to show scott how he used his planing beam for long stock. He typically does the move so quickly (including the footwork) that it was hard for him to slow down to show scott what he was doing. (just looked it up, page 154-155)
>Has anyone ever studied this phenomenon with regard to planes? ... very fast stroke can lower the occurence of tearout ... Any thoughts on this?
Intriguing thoughts, Denis. Generally, I share your impression that stroke speed may matter. But I do get a little bogged down though trying to recall college equations for momentum, force, kinetic energy, work and power. Yet I think I still understand the gist of Newton's Law of the Conservation of Energy.
So any significant analysis of the dynamics probably would have to be in these sorts of terms. As well, there are probably some prinicples of engineering and materials science here...(for instance, an individual blade of grass is basically a vertical beam of cellulose fibers attached at the bottom end to the ground...not unlike a miniature telephone pole...a VW bus at 4MPH wouldn't slice many telephone poles, but a Maserati at 200MPH might). Actually, the blade of grass seems like a pretty fair model to me for a whole bunch of cellulose fibers glued together (wood) and attached to the ground via clamps and a bench, rather than packed dirt and roots.
Maybe, Denis, you should set aside some time and put down your ideas in an article on the topic, if no one can cite a reference that's done it already.
In Thomd's comments about "energy" concentrated at a tiny point (actually I'm thinking of a very fat lady who came to the house and walked around on my southern yellow pine floors in her stiletto heels a few years ago), this energy can be force, as in pressure or push (pounds per square inch), or force as in kinetic energy...slicing at high velocity (a petite young lady in stiletto heels jumping from the second floor balcony). I'm having a flash back to the last paper cut I gave myself. Indeed, any valid theory on planing ought be be able to be generalized to grass cutting, paper cuts, and how axes work at different velocities.
Oh, that's right, momentum is mass X velocity, kinetic energy. Isn't that right? Add a force to raise or lower the velocity of the mass and it accelerates or decelerates, adding or removing kinetic energy.
Anyway, Denis, I think you are correct. Faster ought to mean a "cleaner" cut. Whether it means less tearout, I'm not sure. Let's see: Tearout is splitting fibers from substrate ahead of the cutting edge. They split and fracture and tear in a haphazard, ragged pattern above and below what will be the planed surface. All the fibers separating below that surface will be "tearout". The fiber fragments still attached to substrate after fracture will be cut by the edge, provided they don't bend over like a piece of grass...perhaps depending on sharpness, velocity of the blade, and so forth.
I suspect the major portion of tearout is cause by bundles of fibers splitting away well ahead of the blade, analogous to splitting firewood with a wedge and maul. I'd guess it is about tool angles and the physics of an inclined plane (a ramp, not handplane). I doubt velocity has anything to do with it. You'll recall grandpa splitting wood with momentum, and then the salesmen at HomeDepot demonstrating very slow moving pressure with a hydraulic firewood splitting machine.
Incidentally, I'd guess this probably has been worked out by the forestry and manufacturing industry to answer the question: At what RPM should we be running the 4" diameter planer knifes to minimize tearout in these gorgeous furniture woods from the decimated rain forests of S. America?
>It is difficult to hand plan reversed grain oak without tearout. I only occasionally get tear out on oak with thickness planer. With a molding machine (cutter speed even faster) tear out is almost nonexistant.
>While I don't know how blade speed affects tearout, I do know that thinner chip/shaving thickness reduces it. In thickness planers and molding mahines, higher RPMs result in thinner cuts at a given rate of feed. This could account for less tearout at higher RPMs.
I hear that comparison a lot (planes vs. planers, the difference being speed) but wonder if there is more at work than just cutter speed, namely planing angle. A power planer attacks the wood at almost a right angle, not the same as a handplane which has a much lower pitch. Oak with reversing grain can easily be planed at angles over 50 degrees, especially with a scraper plane. I honestly wonder if any electric planer can give as smooth a surface free of tearout as my 112 (I don't think so). I also buy difficult tropical woods that have been thickness power planed, and alwayd get better results with my hand tools; granted I am finish planing, not thickness planing, but power planers can ruin a surface faster and more extensively than any hand plane.
Furthermore,when I didn't have as much experience with hand tools, I often used to try accelerating my planing strokes when my blade started to get dull (at the first signs of tearout) in the hope of delaying sharpening till after the board was finished. The results were very consistent: tearout was massive, deeper and much more extensive than the previous, slower strokes.
I doubt that speed has much effect on surface quality at the speeds we use hand planes. Skew IME has proven much more effective. Power also might help more than speed (power=mass*acceleration).
>another thing is that most well tuned production planers have a spring loaded chipbreaker bar very close to the cutting action. This helps immensely to reduce tearout, though I believe it can't be equated to tight mouths in a plane, it's function is more effective.
>Frank, skew is just another way of increasing cutting power, or effective sharpness, by lowering the wedge angle. I have seen countless examples of higher speed yielding better surfaces, whether hand planing, or super surfacers, which are just giant motorized hand planes. It's easy to demonstrate just by speeding up your planing. Whether the tactic is worth it depends on what one likes. I don't find it as hard to plane fast on an inclined board. There is something about the hand position change that seems to reduce my otherwise tendancy to twist the plane. Not that I use this position except for strips.
Tear out is another mater though part of the original question. My basic answer is that tear out is less if it would also be less with a blade that was sharper. Tear out occurs in a variety of ways and there are many ways of attacking it. Sometimes the grain is so loose almost anything will knock some out. But at other times the lower drag of a sharper blade might help, and a fast blade has more cutting power than one pushed slowly.
>Thom, as I stated in my original question, "all other things being equal". That includes blade composition, hardness, and sharpness.
The only difference I'm looking for here is, if whether a faster stroke can reduce tearout. My feeling is yes, but I'm asking, so that experienced people can help answer this question. And I value your opinion BTW...
>Denis, I think planing speed is a minor factor in surface quality. If the plane be well set up and the iron sharp there will be no tear out, but I think speed gives a little more shimmer and sheen to such woods as white pine and yellow poplar.
>I think that planing speed does make a difference. But, whether or not a human powered plane can get to a speed that makes a difference is a different issue.
A typical portable planer has a 2" cutter head running at 10,000 rpm. If you work though the math, these plane blades are traveling at close to 60 mph. Another example is a wood lathe. I'm a raw beginner at turning, but I've been able to turn oak and basswood without tearout. For the 6-9" bowls I've done, the wood is also moving at a speed of close to 60 mph.
Now I can hand plane the edge of a 12" long board in about 1 second or so. I'm sure that if I moved fast, I might be able to double or triple my speed. But here we are talking about speeds that top out at 2 mph.
>By shimmer, I meant something akin to a mild chatoyance, a liveliness and depth that is killed by sanding. I used the word sheen to mean that slightly burnished look. The shimmer might be enhanced if there is more sheen. This stuff is rather intuitive; you can't put it under a microscope and measure it. Speed is not necessary to avoid tearout, but if you ask does it enhance the surface, I would say yes, somewhat, especially on softwoods.
>It appears to me as if even the STEM (science, technology, engineering and mathematcis) community does not quite agree on the influcence of cutting speed and cutting force and surface quality. Here's a bit of a summary of the reference I read about during the last few years (meaning [1-3] are cross-referenced in [4]).
Is anybody bold enough to estimate the cutting speed/cutting force of a hand plane? Are data of super surfacers even remotely applicable for hand tools?
1 Rotary Cutters
1.1 Dependence of Cutting Force on Speed:
� for Finnish birch there is not significant correlation between cutting speed and cutting force [1]
� for beach, fir and poplar the minimal cutting force is at cutting speed of 40 m/s (1,575 in/s) [2]
1.2 Dependence of Surface Quality on Speed:
� surface quality improves with increase in cutting speed, but the improvement is offset by fiber damage through rotary cutter) [3]
2. Linear Cutters (after [4])
Measurement conditions for super surfacer:
Skew angles 10, 30 and 50 degrees
Knife projection below sole: 0.05mm (0.002in)
Mouth width: 0.5mm (0.02in)
Blade angle: 30.8degrees
Bed angle: 35 degrees
Chip breaker angle: 35.3 degrees
Distance cutting edge to chip breaker: 0.25mm (0.01in)
Cutting speed: .25 m/min (0.16 in/s or 0.0093 miles/h), 0.5 m/min (0.33 inch/s or 0.019 miles/h) and 0.75 m/min (0.49 inch/s or 0.028 miles/h)
2.1 Dependence of Cutting Force on Speed:
� for fir, there is not significant correlation between cutting speed and cutting force
� for beach, there might be a reduction of cutting force with increased cutting speed (the measurements were not conclusive and could be a results of uncertainties in the measurement setup)
2.2 Dependence of Surface Roughness on Speed:
� there is no measurable change in surface quality of fir and beach for different cutting speeds.
Sources:
[1] Kivimaa, E. Die Schnittkraft in der Holzbearbeitung. Holz als Roh- und Werkstoff, 10 (1952) 3, S. 94-108
[2] Pahlitzsch, G., Jostmeier, H.; Untersuchungen beim Fr�sen von Spanplatten und Schichtstoff-Verbundplatten. Moderne Holzverarbeitung, 3/66- 7/66
[3] Fu�, M. Fr�sen von: Holz und Holzwerkstoffen - Verbesserung von Zerspanungsleistung und Wirtschaftlichkeit, Dissertation, TU Braunschweig, 1995
[4] Fischer, R.: Verbesserung der Oberfl�chenbearbeitung von Holz mit Geometrisch Bestimmten Schneiden durch lineare Schnittbewebung. Final report, AiF-Vorhaben-Nr. / GAG, TU Dresden, 1998
