Why 12 degrees for bevel up planes?

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Blackdiamond2

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So pretty much all bevel up planes, be they block, jack, smoother, jointer or any other are bedded at 12 degrees. I was wondering for what reason was that 12 deg bed angle chosen? I've read that the old Stanley no. 62, the father of all modern bevel up bench planes (I think), had a chipping issue on the rear of the mouth due to the casting being too thin, and the cast iron they were made from was inferior to the ductile iron most good planemakers use today. So I can understand why Stanley would not want to go lower than that 12deg, as it would have made the planes even more fragile.

Bu times have changed. That ductile iron means that planes are tougher, and potentially could go lower. I've been thinking that a 10 degree bedding would make a lot of sense, and that 12 just seems kinda arbitrary today.

Most people who use bevel up planes use a honing jig and microbevels to set the sharpening angles on their irons consistantly, and these jigs often only go in 5 degree increments. The Veritas has a couple in it's eccentric roller, but eclipse styles require you to do a bit of trigonometry yourself to get an accurate sharpening angle that isn't a multiple of 5, as do the Richard Kell guides and most others out there. 10 degrees would be far more convenient to use, as it's a multiple of 5 itself, so all of the other multiples of 5 including common, york and higher pitches would be way easier to grind, as you just add 10 to the sharpening angle. With 12 degrees, you end up having to settle for odd angles like 37, 42, 47 or 62 rather than the cleaner, more accessible 45, 50 or 55. Am I the only one who doesn't know how to set up my honing guide to 38 degrees? Why do people even sell 38 degree blades?

Anyway, the issue boils down to the numbers aren't neat and they're different, so it creates a bit of extra effort if you want to stay aligned with your bevel down compatriots. The bevel up angles with their special +2 degrees will still work just fine, it's just that it's inconsistant for no apparent reason in the modern day. A bit of simplification and streamlining to make things easier to understand isn't a bad thing.

Anyone know if there's a good reason that bevel up planes are bedded at 12 degrees? To be honest this isn't really even and issue and it seem like I'm the only one that cares about this, but I figured I'd ask anyway rather than stew in silence.
 

Steve Maskery

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That, BD, is a very good question.

I do not have the definitive answer, but I can offer a few musings, which might be helpful (or they might just muddy the waters a bit).

On a Bevel Down plane, such as a No4, the cutting angle is set at 45°. It's called Common Pitch. You can change the frog if you want to plane challenging timber. A 50° frog will give you York pitch. In both cases it is the frog that determines the cutting angle. That is why it is not so critical at what angle you sharpen your plane irons. Traditionally they are ground at 25° and then honed at 30°. But it can be pretty much any angle in that general area, as the honing only produces the clearance angle, not the cutting angle. That is set by the frog.

In contrast, with a Bevel Up plane, the cutting angle is determined very much by the grinding and honing angle. So by honing at a different angle, you can change the cutting angle. The clearance angle will always be 12°.

For example, hone the blade to 38°. On a 12° bed that will give you50° York pitch. No need for a different frog. You also get a lower centre of gravity, which some people say is an advantage.

Of course, constantly changing the honing angle will shorten the life of the blade, but you pays your money and you takes your chance.

I have two BU planes, the equivalents of the No4 and the No5. I don't use them as much as I should. For the "No5" I used to have two blades, one at 33° an one at 38°. The 33 went walkabout, I still have the 38, so it is useful when my "proper" No5 is inadequate, which, TBH, is quite rarely. I don't work a lot of difficult wood these days.
 

Blackdiamond2

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Yup, I understand the concept of presentation angle of the plane blade, and how that's controlled by the sharpening angle on a BU plane and controlled by the frog on a BD plane. But this extra 2 degrees on the bed of a BU plane throws a spanner in the works a bit, and makes things different and inconsistant. I imagine it was an engineering decision by the designers at the time, not one that was critical to function, but rather due to durability/manufacturing constraints/size limitations etc etc. Maybe there's some planemaker or someone out there who can explain the rationale behind this 12 degree angle vs any other or a 10 degree angle. Maybe it is an outdated design choice and could be changed, maybe it makes perfect sense for some reason I don't yet know.

I haven't found anything scouring the internet, and everyone seems to take this 12 degrees for granted. Maybe someone on here has an answer, or some pointers to someone that might.
 

woodbloke66

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Not a scoobies why the bed angle is 12deg; I just accept that it is. Steve M above makes some interesting and valid points which I agree with, but just to add a dash of something slightly different, a chap on InstaG mentioned honing a super high bevel of 52deg on a LA plane blade, which then gives an effective pitch on the cutter of 64deg :shock:
I tried this out on a couple of old O1 blades using the Veritas jig which was achievable with care but the result, with a really tight mouth on my Veritas smoother was a revelation on Ebony and African Blackwood, both of which difficult to plane without tear out. I had silky smooth shavings with not a trace of any tear out - Rob
 

Steve Maskery

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woodbloke66":3do979l1 said:
... honing a super high bevel of 52deg on a LA plane blade, which then gives an effective pitch on the cutter of 64deg :shock: ....
(which)was a revelation on Ebony and African Blackwood, both of which difficult to plane without tear out. I had silky smooth shavings with not a trace of any tear out - Rob

That is very impressive.

S
 

Blackdiamond2

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That's great to hear Rob. Both Veritas and Quangsheng have 50 degree blades for sale for their low angle planes, and I thought that was a bit high, but it's cool to know that you can go even higher and it'll still bring benefit!
 

Vann

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I don't know why 12 degrees. Maybe any lower creates problem with clearance?
Blackdiamond2":2kvhtboi said:
...Anyway, the issue boils down to the numbers aren't neat and they're different, so it creates a bit of extra effort if you want to stay aligned with your bevel down compatriots. The bevel up angles with their special +2 degrees will still work just fine, it's just that it's inconsistant for no apparent reason in the modern day. A bit of simplification and streamlining to make things easier to understand isn't a bad thing...
Blackdiamond2":2kvhtboi said:
...But this extra 2 degrees on the bed of a BU plane throws a spanner in the works a bit, and makes things different and inconsistant...
I've never worried about it. I can't think why I'd want to "stay aligned" with my bevel down planes - except maybe initially to make a comparison.

Just sharpen your irons at 5 degree multiples and work at 47/52/57 degrees - it doesn't matter.

And by the way, buy your BU irons at 25 degrees and hone any microbevel you want.
woodbloke66":2kvhtboi said:
... honing a super high bevel of 52deg on a LA plane blade, which then gives an effective pitch on the cutter of 64deg...
A 50 degree microbevel (even on a 25 degree bevel iron) will give you an effective pitch of 62 degrees - which is as near as dammit - and no hassles finding angles that aren't multiples of 5 degrees.

My tuppence worth.

Cheers, Vann.
 

Woody2Shoes

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The old boys always worked on ratios rather than absolute measurements. They also liked the number 12 for its divisibility. 12 being one thirtieth of a circle! Two degrees either way on a blade is really nothing. Thirty degrees - a twelfth of a circle - is two along and one up - same idea - good for freehanding - I'm starting to invoke the memory of Jacob...
 

samhay

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Blackdiamond2":2lm1u7xw said:
... the father of all modern bevel up bench planes (I think), had a chipping issue on the rear of the mouth due to the casting being too thin, a...So I can understand why Stanley would not want to go lower than that 12deg, as it would have made the planes even more fragile.

I expect you answered your own question regarding why 12o. This was settled on by Stanley, possibly with much trial and error, and there hasn't been a great deal of innovation since.

Blackdiamond2":2lm1u7xw said:
...Most people who use bevel up planes use a honing jig and microbevels to set the sharpening angles on their irons consistantly,

I expect you will find this is not the case. There is a lot of freehand sharpening going on by a lot of folk that both do and don't regularly frequent forums.
 

Woody2Shoes

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Blackdiamond2":1gbr74qu said:
...I've read that the old Stanley no. 62, the father of all modern bevel up bench planes (I think), had a chipping issue on the rear of the mouth due to the casting being too thin, and the cast iron they were made from was inferior to the ductile iron most good planemakers use today. So I can understand why Stanley would not want to go lower than that 12deg, as it would have made the planes even more fragile....

I don't know enough about old wooden planes but I strongly suspect that the angles were worked out e.g. 'York pitch' before metal planes became widespread.
 

Blackdiamond2

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Yeah, as most of you are rightly saying and as I did mention in my original post, this is basically a non-issue. It would just be cool to know definitively the reason for that angle though - I find challenging assumptions or knowlege we take for granted (in this case, seemingly without a clear reason) to be refreshing and a great way to innovate and move forward. A lot of that has happened in woodworking over the past decades!
 

Vann

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And no one has mentioned that probably the majority of Stanley's LA BU planes were 20 deg: No.110; No.120; No.130; No.220 etc.

Cheers, Vann.
 

AndyT

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I reckon that they will say it's the lowest angle that's practical to make in that position on a casting.

At 12 degrees the edge of the bed is pretty fragile but stands a chance of surviving. Lower it to 10 and they'd get a slew of reject castings, followed by a stream of returns where the edge crumbled or got chipped in use.

And it's not like all the users of 12° planes are complaining that their planes don't work because the angle is too high.
 
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