Thread: Low angle vs. High angle Planing

I am sticking my neck out here, but I think there are mistakes in Derek's and IanW's posts. Derek said that "these are bevel-down planes" referring to the LN 164. As I understand it, it is in fact a bevel-up plane, and I think that is what Derek meant to say, since he goes on to say that the effective cutting angle depends on the angle of the bevel that you hone on it.

Second, as Silent C correctly understands, the cutting angle (in a bevel-down plane) is the angle between the plane's sole and the top of the blade (assuming no back-bevel), not the angle between the perpendicular to the plane's sole and the top of the blade, as IanW's diagram shows.

IanW's point, about there being a lot of blade 'floating' in bevel-down planes with a thick blade, has been addressed in the Veritas planes, where the frog actually extends downwards through the sole of the plane in order to provide maximum support for the blade.

Rocker

IanW's post shows the cutting angle as it's defined in engineering terms:

cutting angle = rake angle (alpha) = back rake angle (USA nomenclature)

OK, well it all sounds like semantics to me but the thing that really has me confused is Derek's statement that...

... low blade angle planes are not really low blade cutting angle planes!! These are bevel-down planes, and the effective cutting angle is around 45 - 55 degrees (depending on the angle of the blades bevel).

Maybe I'll have to wait until the sun comes up in Perth to find out what he means. Not having read anything much really about this stuff, I am relying upon my intuition (possibly a bit too much). Given the very flat angle of the bed of that Lie-Nielsen plane, bevel up or bevel down, I can't see how we get a 45 - 55 degree cutting angle out of it.

OK, if Rocker is correct, then it all makes sense. Derek is saying that the low angle plane has a bevel up blade and so the cutting angle is greater than the bed angle. By implication he is saying that therefore the cutting angle on the low-angle plane can approach the cutting angle of a high-angle plane if the bevel on the former is say 30 degrees and bevel up, whilst the blade in the high-angle plane is bevel down.

So the only real difference is the relative position of the rest of the metal in the blade and how it interacts with the frog.

Incidentally, from the Lie-Nielsen site:

The blade sits in the body at 12°. It comes with a 25° flat ground bevel, making the included cutting angle 37°.

It is shown bevel up.

[QUOTE=silentC]Ian,

What you are saying in that diagram is that the cutting angle is actually the number of degrees that the leading edge of the blade is off the perpendicular, not off the horizontal. So for a more acute cutting angle, the leading edge of the blade is actually presenting to the wood at a steeper angle. "

Hmm, I cocked that up a bit in my haste - there is a bit of argument about which angle should be called "cutter angle" (see Zitan's post above) - I think you are correct that most woodies use "Cutting angle" as that measured from the horizontal to the leading edge of the blade....

What I wuz trying to make clear is that the cutting angle is changed by turning the bevel up, because we add the bevel angle to the bed angle, whereas with bevel down, the only difference bevel angle makes is to the clearance.
And what Derek is saying (I think) is that if you take a standard block plane, which is usually bedded at something between 15 and 20 deg., and add the sharpening angle, (25-30) you get a (woody's) cutting angle of 40 to 50 degrees, putting them squarely in the range of Mr. Bailey's design.
Apologies to all I inconvenienced!
Yeah - I noticed Derek's post was at about 3 AM our time - must be a real late-nighter!
Cheers,

Australian Wood Review number 39 has all the answers on pages 80-83 (article by Terry Gordon). Just for the record,
Cutting Angle is measured from an imaginary line at 90deg to the surface of the wood (scraper = 0deg, HNT Smoother=30deg, Stanley=45deg).
Blade Angle is measured from horizontal or the surface of the wood (HNT=60deg, Stanley=45, Scraper=90deg).
Bed Angle is an easy one and for a bevel down plane will equal the blade angle until you complicate things by adding back bevels.
As I see it, it doesn't matter if they are engineering terms or not, the angles have been given names, there's only four of them so we should try to understand and use them in their right context...........please.

Thanks Dan. I'll have to get a back issue and read that one.

The trouble is that already we have two contradictory sources. The Lie-Nielsen site has cutting angle as the acute side of the angle measured from the horizontal: bed angle + bevel angle. Terry Gordon has it as the angle measured from the perpendicular: 90 deg. - bed angle + bevel angle. Both are plane makers and should know, so who do we believe?

The former makes more sense to me as it seems that the lower the angle, the flatter the blade should be in relation to the job. I don't understand how the alternative is useful when describing the cutting angle, because it implies a sharper cutting angle is actually presenting more steeply. The imaginery perpendicular line is imaginery and so why do we need it at all? Unless this has something to do with the physics of chip formation.

So in the Terry Gordon parlance, a smaller angle approaches a scraping action, and a larger one approaches a slicing one. In the Lie-Nielsen parlance, the opposite is true. Either way, when you are talking end grain, you want a slicing action do you not? So at some point as the angle of the grain rotates through 90 degrees, does the slicing action become detrimental? Why is a scraping action better in some cases?

:confused: :confused:

Dan (quote),

"As I see it, it doesn't matter if they are engineering terms or not, the angles have been given names, there's only four of them so we should try to understand and use them in their right context...........please."

Totally agree, but certain people have put it the other way (see various posts above). The main issue is that we all agree that the important angle is the one between the top of the blade, be it the beveled surface (block, shoulder, mitre planes) or the 'flat' of the blade (most bench planes) and the wood that affects how it cuts. The bed angle of the blade is somewhat irrelevant, except to do the maths.

It seems intuitive to me to measure cutting angle from the vertical, as our metal-working and turner colleagues do, but some like SilentC obviously don't find it so. C'est la vie....
cheers again,

Just looking at the quote from the Lie Nielsen site by SilentC, they call it an included cutting angle and something from my school days tells me that thats a bit different than just saying "angle", I could easily be wrong. Then you have another maker calling the blade angle an "attack" angle,
http://www.woodworkforums.ubeaut.com...ead.php?t=5162
Then with router bits and saw blades they use the terms Rake and Hook angle which I understand to be the same as Cutting angle.
I also noticed when reading the Australian Timber Buyers Guide that with some species, ie Blackwood, that "planer blade angle may need to be reduced, especially for figured material". Do they really mean Cutting angle (as you would expect), or not. :confused:
It looks like it might be too late to have a simple explanation for this one unfortunately.

In plane geometry, the included angle is the angle at which two planes that are not parallel meet. In this case, that would be the blade bevel (for bevel up) and the sole of the plane. So if Lie-Nielsen are providing another alternative to cutting angle, we now have 5 to worry about. Don't you just hate relativity?

Dan,
From school trigonometry, an included angle is just any angle between two specified lines.
The term 'attack angle' has merit - implies a businesslike purpose!
Never did know what the advice about 'reducing planer angle' meant - it's in Bootle, too. I can only presume they are advising putting a back bevel on your planer blades. The other way you could affect the attack angle on a rotary planer is to put some angled shims in front of the cutters- a bit of a hairy undertaking!

As to the confusion, what do you expect once the Yanks start buying in - they've stuffed the language, now they're trying to confuse our visio-spatial senses.
I'm going for some lunch!

I found the following at http://countryworkshops.org/glossary.html

Clearance angle. The angle between the lower face of a blade and the wood being cut.

Cutting angle. (rake angle) The angle between the upper face of a blade and the wood being cut. The cutting angle equals the included blade angle plus the clearance angle.

Included angle. The angle formed by the two facets of a cutting edge.

Dan,
Thanks for drawing our attention to the Terry Gordon article. It does indeed seem that there is a contradiction between American and Australian usage in regard to the term "Cutting angle". I was taking my information from the diagram in the instruction book for the Veritas bench planes, which refers to the angle between the sole of the plane and the uppermost part of the blade as the "Effective cutting angle". I have to admit that, lacking as I do an engineering background, I agree with Silent C that the American usage is intuitively more natural.

It seems that, just as with the word "fanny", there is endless potential for disastrous misunderstandings in the different usages of our American friends

On the other hand, another American, Nick Engler, in his book "Sharpening", follows Terry Gordon's usage of the term "Cutting angle". So, it seems yer pays yer money and yer takes yer choice.

Rocker