Thread: Bevel down, bedding angle and primary bevel

Originally Posted by monoman

Hiya,

Will a bevel down plane work if the blade is ground to just slightly less than the bedding angle? i.e. 45 deg bedding angle and 44.5 deg blade.

Why do planes with a 45 deg bedding angle typically use a 25 deg primary bevel.

My guess is that the wood doesn't care what happens behind the cutting edge, but a lower primary bevel my wear slower.

Cheers

Hi monoman.

You will find the attached information should assist you.

Select "Other Peoples Conclusions" from the listing shown.

Most thoughts on blade bevel refer to a bed angle of 45 degree's.

regards: planemaker.

http://members.shaw.ca/petermichaux/...harpening.html

Originally Posted by monoman

Why do planes with a 45 deg bedding angle typically use a 25 deg primary bevel.

Their is no real reason. Why you cannot used 20º, 25º, 30º, 35º, I think however you need a clearance angle behind the plane blade.

The greater the angle the more durable the edge will be.

Originally Posted by planemaker

Hi monoman.

You will find the attached information should assist you.

Select "Other Peoples Conclusions" from the listing shown.

Most thoughts on blade bevel refer to a bed angle of 45 degree's.

regards: planemaker.

http://members.shaw.ca/petermichaux/...harpening.html

Sorry, but I can't see how this article answers my question. Maybe it's me. If I understand this article correctly, they are talking about a 45 deg bedded angle and a 30 deg included angle.



Cheers

Originally Posted by thumbsucker

Their is no real reason. Why you cannot used 20º, 25º, 30º, 35º, I think however you need a clearance angle behind the plane blade.

The greater the angle the more durable the edge will be.

Why does it need a clearance angle behind the blade. Bevel down planes don't have clearance behind the blade.

And if the greater angle is more durable, why not the same as the bedding angle.

Originally Posted by monoman

Sorry, but I can't see how this article answers my question. Maybe it's me. If I understand this article correctly, they are talking about a 45 deg bedded angle and a 30 deg included angle.



Cheers

Leonard Lee # 30 - 35 p.b
Brent Beach # 25 p.b
James Krenov # 30 p.b
Lee Valley # 30 p.b
Lie Nielson # 25 p.b

planemaker:

Originally Posted by planemaker

Leonard Lee # 30 - 35 p.b
Brent Beach # 25 p.b
James Krenov # 30 p.b
Lee Valley # 30 p.b
Lie Nielson # 25 p.b

planemaker:

Given the wide range of angles, they can hardly be anything but personal preference. A bevel down plane presents the cutting edge to the wood as the sum of the bedding angle and the angle of the primary (or secondary) bevel on the blade. And it works without behind the blade clearance. So why not bevel up?

Good question.. one of those that I have never bothered to ask.. it just is because it is, so it is
... but now that you have asked, I find myself wanting to watch this thread awaiting an explanation.

My only assumption from looking at old blades and the way their owners sharpened them down (we're talking pre tormek and sandpaper float glass here) is that by grinding your blade at 25-30 you would then increase this every time you went to the stones until you got dangerously close the 45 (or whatever your bedding is) then it's time to grind again. By grinding closer to the 45 you are giving yourself less working time between visits to the grinder.

(I'm not saying this is great practice but a heap of blades that I have seen would suggest it to be a pretty common)

Makes sense to me.. esp with the thick tapered blades of the woodies.. the loss of steel behind your edge on a 30 degree grind isn't really going to be noticable.. maybe on a thin modern Stanley

good thread

Originally Posted by monoman

Given the wide range of angles, they can hardly be anything but personal preference. A bevel down plane presents the cutting edge to the wood as the sum of the bedding angle and the angle of the primary (or secondary) bevel on the blade. And it works without behind the blade clearance. So why not bevel up?

my reference here is Leonard Lee's The Complete Guide to Sharpening (Taunton)

Bevel UP planes (block planes, low angle smoothers, etc)
the clearance angle = the bedding angle (the flat side of the blade is down and at the same angle as the bedding angle)

Bevel DOWN planes (Stanleys and the like)
the clearance angle = the primary bevel
the flat side of the blade is UP and at the same angle as the bedding angle (typically 45°)

The clearance angle, is there to allow the wood fibres somewhere to spring back into after being cut

Originally Posted by monoman

Given the wide range of angles, they can hardly be anything but personal preference. A bevel down plane presents the cutting edge to the wood as the sum of the bedding angle and the angle of the primary (or secondary) bevel on the blade. And it works without behind the blade clearance. So why not bevel up?

Hi monoman.

The preference of primary bevel is a range of 25 - 30 degree's.(not including micro bevel ). What's important to note in answering your question is why the choice does not exceed 35 degree's. Read the following:

Lee Valley bench plane instructions:

"The Veritas bench plane blade comes honed ready for use, with a 30 primary bevel and a 35 micro-bevel. This configuration provides a strong, long-wearing edge that can be quickly honed many times before the primary bevel needs to be reground. The 35 micro-bevel leaves a 10 relief angle; more than adequate to accommodate the springback of the wood fibers."


planemaker.

The clearance angle is necessary to prevent friction between the back of the blade and the wood surface. When planing, there is spring back of the wood surface. The resulting friction will create wear on the blade.

Leonard Lee suggests that 12 degrees "is more than enough".

With bevel down planes the minimum clearance is easy to achieve. With the Common pitch (the lowest typical bedding), which is 45 degrees to the unwashed, a face bevel of 35 degrees will still leave a clearance angle of 10 degrees.

I very much doubt that you would enjoy using a high angle like this, or one especially high, such as 44 degrees, since the edge will not feel sharp. It may last longer, but it will not cut as well. Even a router plane, such as the Stanley #71, uses a clearance angle for the cutter. It is not flat to the surface as its appearance suggests.

One of the criticisms levelled at bevel up planes is that they lack sufficient clearance. BU planes actually have 12 degrees of clearance if their bed is at 12 degrees. As a result of the friction, wear takes place at the back of the blade. This is termed the "wear bevel". It will blunt the blade eventually ... in theory ... although photographic evidence of this wear bevel has been documented by Brent Beach, I am a little cynical that the criticism is overdone.

For start, BU planes are used by a lot of woodworkers and I do not hear complaints of the edges not lasting very long. Secondly, there are ways to avoid the wear bevel developing.

The first way is to use the Ruler Trick (of David Charlesworth) to add a fine micro backbevel to the BU blade. The second is the method I advocate, that is to strop the blade between honings (this is done primarily to extend the sharpness of an edge).

For dedicated BU smoothers the future will see beds higher than the current 12 degrees. Already Karl Holtey has a 22 degree bed in his #98, and Philip Marcou (at my urging) created a 20 degree bedded BU smoother. I have built a 25 degree BU infill smoother (which allows me to use a 35 degree bevel face - which is easier to freehand than a higher bevel).

Regards from Perth

Derek

Originally Posted by Slow6

Good question.. one of those that I have never bothered to ask.. it just is because it is, so it is
... but now that you have asked, I find myself wanting to watch this thread awaiting an explanation.

My only assumption from looking at old blades and the way their owners sharpened them down (we're talking pre tormek and sandpaper float glass here) is that by grinding your blade at 25-30 you would then increase this every time you went to the stones until you got dangerously close the 45 (or whatever your bedding is) then it's time to grind again. By grinding closer to the 45 you are giving yourself less working time between visits to the grinder.

(I'm not saying this is great practice but a heap of blades that I have seen would suggest it to be a pretty common)

Makes sense to me.. esp with the thick tapered blades of the woodies.. the loss of steel behind your edge on a 30 degree grind isn't really going to be noticable.. maybe on a thin modern Stanley

good thread

I think Luban's got it. It's easy to forget that every minute away from the work would be money lost especially with a slow hand-turned grindstone needing the apprentice to do the grunting.
It's like subsistance farming. You stick to what has worked in the past rather than experiment and risk losing.
Jim

I've been digging around looking for evidence that supports bevel angle theory, and so far, I haven't found anything even close. There are many good arguments put forward, such as Terry Gordon's, see http://www.hntgordon.com.au/newsletterbladeangles.htm

Some people have mentioned something called a "clearance angle", and how it must be present for the wood fibers to spring back, otherwise the plane body creates too much friction on the wood. This one sounds fishy to me. As an example, I offer thumbsucker's drawing from the "Let's design a plane thread", https://www.woodworkforums.com/attach...2&d=1221693404

I don't see no clearance angle there, and I'm sure most BU planes only have a clearance angle because of manufacturing constraints. If clearance angle was important I'm sure there would be a whole heap of armchair experts with mystical theories about optimum clearance and and length. Since, if you are going to need clearance for the wood fibers to spring back, then how long does it need to be, because by clearance angle we mean the gap between the cutting edge of the blade and the body of the plane starting from the rear edge of the mouth. Would a gap of .001" do? Would .200 be better? See what I mean?

Also, I have seen many close-up photos of a plane iron cutting wood and I've never seen wood fibers springing up.

Originally Posted by monoman

....
I don't see no clearance angle there, and I'm sure most BU planes only have a clearance angle because of manufacturing constraints. If clearance angle was important I'm sure there would be a whole heap of armchair experts with mystical theories about optimum clearance and and length. Since, if you are going to need clearance for the wood fibers to spring back, then how long does it need to be, because by clearance angle we mean the gap between the cutting edge of the blade and the body of the plane starting from the rear edge of the mouth. Would a gap of .001" do? Would .200 be better? See what I mean?

Also, I have seen many close-up photos of a plane iron cutting wood and I've never seen wood fibers springing up.

Monoman - you would need rather good eyes or a microscope to observe the springback in most woods, but it is there, nevertheless. ALL cutting edges need clearance, because ALL materials experience some compression ahead of the cutting edge and all spring back to greater or lesser extents after the compression is relieved - even metals, it's an inviolable law of physics. The easy answer to your dilema is the empirical one - go try setting up a series of blades with zero clearance & see what they do for you (not much!).

You can't (by any practical process available to your average woodie) increase the clearance angle on a BU blade - putting a back bevel on it would only decrease clearance....

There is always a compromise between 'sharpness' & 'edge retention' - the ideal cutting edge would be two superimposed parallel planes - i.e. of infinite 'thin-ness' - but it would have rather little edge retention, since by definition it would have no material at all in it!

Most of us settle by trial and error, on a bevel that is a suitable compromise for us between 'sharpness' & edge holding under the variety of conditions we expect to use it in. The 25/30 (grind/hone) recommendation for bevel-down 45 degree bed angles is a pretty good comproimise for most cabinet woods. Increasing the included angle of the blade for hard stuff MAY increase edge retention, but it also slightly increases the effort required on each stroke - maybe unnoticably at first, but increasingly as the edge dulls.

My 2c,

As I have previously alluded, I'm looking for evidence. I have been searching various academic publications and trade journals for evidence-based information. Too date, I have found the following article, "Wear and Blunting of the Tool Corner in Cutting a Wood-Based Material" By W. M. McKenzie and H. Karpovich
Commonwealth Scientific and Industrial Research Organization, Division of Btiilding Research,
Melbourne, Victoria, Australia - See attached pdf preview.

I have just purchased this article for USD$34.00. I am serious about evidence based information, aren't I.

I am happy to forward the article to anyone that wishes to read it with the following proviso. Only one copy of this article can be in *use* at any one time. I will keep an archival copy. Once you have read it, please notify me that you have destroyed your copy, and I will make it available to the next party.

I will need to read it myself first.