Planing - exact relationship between depth and effort?

[Corneel]

When you really want to measure planing forces you need to measure in two directions. The horizontal pushing force, but also the vertical force on the edge. It can either pull the edge into the wood or push it out. That is important for the planing experience too.

That's what mr. Walker and mr. Goodchild did back in 1960. And that is still the way everyone measures forces in woodcutting experiments.

 

[Dangermouse.]

I don't know and I don't care ! (hammer)

 

[Phil Pascoe]

That's OK - I suspect the OP didn't have you in mind when he posed the question.

 

[RossJarvis]

I think you may need to rethink a bit on the mechanical forces and think more about the source of labour, in this case bloke-power. With a lot of the force calculations etc the input effort is related to machinery. With blokes, other factors come into play, such as tea and hob-nob consumption and the "getting knackered differential".

In my experience, although doubling the effort by increasing depth of cut by "x" for instance may mean that 4 passes of the plane equal 8 passes at setting "Y", I find that I can plane all day at the lighter cut, but only for 3 minutes at the harder cut. So the result of taking a greater cut may appear to be equally efficient, in actuality it isn't.

However, bearing in mind I only use a Record 5 1/2, despite possessing three No 4s, A 4 1/2, A wooden 4ish and a wooden 5 and a bit-ish, plus all the others I've forgotten about, also means picking the thing up nearly kills me. (But, once it starts it'll go further than anything else).

Furthermore, If you accept Schroedinger's theories, you'll find that if there is a cat inside the box you are planing, it will be very difficult to be certain about the outcome of any experimentation regarding depth of cut anyway (or is that Heisenberg?).

 

[MickCheese]

Now I too think this is crazy, do you have OCD?

But

I will wade in with a suggestion :?:

Pull the plane with a spring balance like they test brakes on a motorbike for the MOT. That should give you a reading at every depth you chose, but so many variables like sharpness.

Mick

 

[Random Orbital Bob]

sharpness?? Did someone mention sharpness. Sh.

 

[tobytools]

I enjoy the forum and the threads but this is so OTT

This is plane mad

Coat.....

TT

 

[SammyQ]

Come on chaps! This thread dug up some nice science for BB and like minded others, so Poo on all you Philly-stines.............geddit? Philly? Planes? Wot Bugbar said? I'm off...

Sam

 

[Jacob]

When you want to know something about plane cutting forces, have a look here:

http://www.amgron.clara.net/sciencereport16.html

For normal cutting angles there is a 1:1 relation between cutting depth and cutting force in the horizontal direction. The force you feel when pushing against the plane.

Can't be true, or there would be no point in ever adjusting depth, or in camber, or in scrub planes etc etc. Obvious nonsense.

 

[Corneel]

Huh? Don't understand you Jacob. Cutting force increases with cutting depth. That's pretty obvious. Doubling cutting depth doubles the horizontal force, more or less. I have the entire article and it is universal for all the woodtypes they tested. It's the same for cutting width. Double the width of the cutter and the force doubles too.

They didn't test the effect of camber so you can't draw conclusions about that.

 

[Jacob]

Huh? Don't understand you Jacob. Cutting force increases with cutting depth. That's pretty obvious. Doubling cutting depth doubles the horizontal force, more or less. I have the entire article and it is universal for all the woodtypes they tested. It's the same for cutting width. Double the width of the cutter and the force doubles too.

They didn't test the effect of camber so you can't draw conclusions about that.

It contradicts everyday experience i.e. that it's quicker and easier to remove material with a deeper cut.
Two thin shavings require much more effort than one thick one as there is twice as much plane movement (the heavier the plane the more the effort) and also twice as much friction. Other factors too I expect.

They didn't test the effect of camber so you can't draw conclusions about that

I can draw the conclusion that they didn't do a meaningful test of planing action and that their conclusions are wrong as far as actual plane use is concerned.
In fact, as we all know, cutting force required for removal of a given volume of material, when actually using a plane, reduces with depth of cut, up to a point.

 

[Corneel]

Well Jacob, I really wanted to prove you wrong, but I think you are onto something. Walker meassured cutting force on the blade and they did that perfectly allright. On closer inspection of the curves I see a shallower line. For example the 52.5 degree cutting angle. The gradient is 1 : 0.8 Only at a higher cutting angle you come close to 1:1. But jackplanes are 45 degree cutting angle.
A second point, Walker only mesured up to 60 um which is just over 2 thou. Jack plane shavings are much thicker. I looked for other literature and found Porankiewicz, main and normal cutting forces by machining wood of pinus sylvestris. He describes a parabolic curve for a cutting depth of 0.1 to 0.5 mm. It's a slower curve then a linear one. Going from 0.1 to 0.5 mm I see a 1 : 0.5 gradient. This is at a 60 degree cutting angle. Lower angles would have an even slower rising curve.

Btw I think the frictional influence is small as long as you keep the plane sole waxed.

Us being weak humans I think the most important thing in jackplaning is choosing a cutting depth that is easy to maintane. 0.5 mm thick shavings wear you out too soon. Something around 0.2 is much easier to do over a longer period of time.

Edited for a calculation error