Clearance in BD plane

[Pat Barry]

Except of course that that's not how it works in reality.

Take a close look at the micrographs Kees posted several updates back. Wear causes a very small (tenths of an mm at most) zone of ZERO clearance to form behind the edge, and it does so regardless of the initial clearance of the blade.

This is actually extremely simple common sense. Imagine taking the corner of a piece of metal to sandpaper at varying angles. If you tilt it at 10 deg the sandpaper will abrade a 10 deg bevel (i.e. zero "clearance") on the corner. If you tilt it at 20 deg, then the sandpaper will abrade a 20 deg bevel (zero "clearance" again) on the corner. Why should blade wear be any different?

Where clearance angle probably does make some difference is in how quickly that flat spot grows. Obviously as you tip the piece of metal further on edge that forces you to abrade away more material for any fixed size of the flat spot. I suspect that benefit is second-order, though.

So, with an acute bevel angle (25 for example) as compared to a more obtuse bevel angle (34 for example), all else being equal, the blade edge should not last as long and the number of shavings in this test should be reduced. I don't think the results of the experiment match expectations. The only conclusion is that the test had another variable that affected the results. I don't think a discovery was made with the test either so a repeat test is in order.

[Warren Mickley]

One of the problems with the test is that both the clearance angle and the bevel angle were varied simultaneously. It is difficult to separate which was the dominant factor. And in addition the test was done without the normal downward pressure; it tested only the irons ability to grab hold of the board and take a shaving. I think this would tend to bias the results toward a more acute honing angle, regardless of the clearance angle.

[Jim Koepke]

This is actually extremely simple common sense. Imagine taking the corner of a piece of metal to sandpaper at varying angles. If you tilt it at 10 deg the sandpaper will abrade a 10 deg bevel (i.e. zero "clearance") on the corner. If you tilt it at 20 deg, then the sandpaper will abrade a 20 deg bevel (zero "clearance" again) on the corner. Why should blade wear be any different?

There is a difference between passing a piece of metal over an abrasive and passing a sharp edge over wood. For one, when working a bevel on metal against abrasive there isn't a need for a relief angle. Another is the abrasive sheet is more likely to 'bubble' in front of the metal. In the video by Professors Kato and Kawai it is possible to see the wood being planed actually rebounding behind the cutting edge. I'm not an expert in physics, but it is my guess that this wood rebounding is part of the reason a blade needs to have a relief angle. With a relief angle of 20º there is a lot more room for wear to the bevel and relief angle than with there is with a relief angle of 10º.

It is also likely this will have more effect when one is making light shavings as compared to thick shavings.

One indicator of blade wear is how thin of a shaving the blade can make.

jtk

[Normand Leblanc]

One of the problems with the test is that both the clearance angle and the bevel angle were varied simultaneously. It is difficult to separate which was the dominant factor.

How can it be otherwise? If the bevel angle is changed/varied then the clearance angle (relief angle) is also varied.

Here is a study.
http://planetuning.infillplane.com/h...ron_study.html

One of the conclusion is:

"The force perpendicular to the direction of planing reverses with distance planed. Initially the blade is pulled into the wood surface, but as the blade gets dull, in particular that the flat spot develops on the back (beveled side) of the blade, the blade is pushed away from the surface. In hand planing these forces would initially pull the plane into the planed surface, but with dulling, the plane would be pushed away from the surface "

For me, the most important factor that determine when I need to resharpen is the pressure that I have to add on the front knob. In normal planing, once the blade is well engaged, I do not apply any pressure in the front. If you do, how do control the end of the cut...you will most likely round up the end of the board.

Pat,
Why don't you sharpen at 45 with the bevel parallel with your wood? The reason is that you would not be able to engage a cut because the large surface of your bevel would require an enormous amount of vertical force for the blade to engage a cut. This is one of the reasons we have a relief angle. The question that I'm trying to answer is "what is the best angle".

I've started those test because it was obvious to me (may have to do with my sharpening method) that I was getting more life from BD blades compared to BU. So far it seems that 25 degrees is the best angle for soft wood at least. Much better than 35 degree.

[Patrick Chase]

There is a difference between passing a piece of metal over an abrasive and passing a sharp edge over wood. For one, when working a bevel on metal against abrasive there isn't a need for a relief angle. Another is the abrasive sheet is more likely to 'bubble' in front of the metal. In the video by Professors Kato and Kawai it is possible to see the wood being planed actually rebounding behind the cutting edge. I'm not an expert in physics, but it is my guess that this wood rebounding is part of the reason a blade needs to have a relief angle. With a relief angle of 20º there is a lot more room for wear to the bevel and relief angle than with there is with a relief angle of 10º.

We're talking about two different things here.

Yes, wood compresses and rebounds, and you need relief to deal with that . That was actually my entire point in starting this thread (seriously, look at #1). I also specifically acknowledged that again when I replied to you in #39. I'm not sure why this keeps coming up as though it were a topic of debate or relevant to my points about wear. It is neither.

Now with that out of the way, can you please look at the micrographs Kees posted? They show pretty clearly that the wear patch is flat (zero clearance).

[Pat Barry]

Pat,Why don't you sharpen at 45 with the bevel parallel with your wood? The reason is that you would not be able to engage a cut because the large surface of your bevel would require an enormous amount of vertical force for the blade to engage a cut. This is one of the reasons we have a relief angle. The question that I'm trying to answer is "what is the best angle"..

Oh yes, I see all that and agree that the more acute angle will cut better, at least to start. All I'm saying is that it was surprising that your results showed that the more acute angle held up longer by producing 2 mil shavings significantly longer than the more traditional bevel angle.

[Normand Leblanc]

I was also surprised. I was thinking that 30 maybe more would be the best angle. Anyway, I've redone all that test and, even if there are some differences, 25 degrees is still the best angle by far...in soft wood... with a Record blade. Just wait a few more days and I'll have a decent study to show with plenty of data to discuss.

Right now I've began testing a Stanley blade and it doesn't look good at all so far. Much worse than a Record blade. In fact it's not even a surprise for me.

http://oldchips.blogspot.ca/2016/05/...iron-with.html

[bridger berdel]

George-
This group is self-selected for liking to chatter on the internet. What the actual topic is may be not so important...

For heaven's sake. You guys can dwell on nothing of importance forever. The real point is: can you USE your tools to make beautiful things. Do you know design? Can you draw(knowing design does not mean you can draw). Can you do accurate work? And several others.

[Stewie Simpson]

Excellent work Normand. Question for you regarding the results you posted within your link; can you explain how you ended up with an included angle of 48* when the bevel angle is only 35*.

https://www.youtube.com/watch?v=UFMy2knKAwI

regards Stewie;

[Jim Koepke]

All I'm saying is that it was surprising that your results showed that the more acute angle held up longer by producing 2 mil shavings significantly longer than the more traditional bevel angle.

Isn't the traditional angle for Stanley blades 25º?

Maybe these tests were done way back in the beginning of plane use.

jtk

[Stewie Simpson]

Normand; re the results you posted. If dykem were to be applied to the bevel of the plane iron before each of the following 5 tests; would that have highlighted any changes within the wear pattern as the relief angle was progressively reduced.

The results for a 0.002" shaving are:

	sharp. Angle	Relief angle	# shavings
Test 1	25	20	120
Test 2	28	17	95
Test 3	31	14	90
Test 4	34	11	70
Test 5	37	8	35

[Normand Leblanc]

Haha!
The geometry is quite simple. All those irons have been sharpened with a 3 degree backbevel. I think that by doing this I rapidly remove the wear bevel.

As for "dykem", english being a second language for me, I presume that it means like coloring/painting. If it's the case, I doubt that it would show anything but, having more test to do I'll give it a try and let you know.

Good night

[Stewie Simpson]

Isn't the traditional angle for Stanley blades 25º?

Maybe these tests were done way back in the beginning of plane use.

jtk

Jim. Its funny you should mention that; yesterday during a cleanout of the workshop I came across an old instruction manual that's supplied with a Stanley Bench Plane purchase, and it states; The cutter is supplied at a ground angle of 25*. Before use the cutter must be honed at 30*

Stewie;

[Steve Voigt]

I was also surprised. I was thinking that 30 maybe more would be the best angle.

Well, that is one mark of a good test, when the results surprise you or seem a little counterintuitive; it suggests that you didn't let your own bias control the test. But you repeated the test and got (basically) the same results, which suggests to me that the test is valid and useful.

I see some people complaining that the test is not "real world" enough. The truth is that there never has been, and probably never will be, a test that exactly duplicates real working experiences. You always give up a little reality, in order to simplify and quantify. But that doesn't mean that the test isn't useful. I think what's really going on is that these people feel threatened by data that contradicts their entrenched outlook. Oh well, too bad for them.

My one caveat is that you are taking thin shavings in softwood; I wonder if the results would be the same with harder woods and/or thicker shavings. I suspect not, but I don't really know.

Anyway, I'm looking forward to seeing the rest of your data.

[Jim Koepke]

We're talking about two different things here.

Yes, wood compresses and rebounds, and you need relief to deal with that . That was actually my entire point in starting this thread (seriously, look at #1). I also specifically acknowledged that again when I replied to you in #39. I'm not sure why this keeps coming up as though it were a topic of debate or relevant to my points about wear. It is neither.

Now with that out of the way, can you please look at the micrographs Kees posted? They show pretty clearly that the wear patch is flat (zero clearance).

Yes, you brought up rubbing metal on an abrasive and my comment is it is totally different than a blade on wood.

From your post #1:

The reason I'm posting this is because I'm firmly of the opinion that extra clearance is nothing more than wasted blade life, so it pays to know where the real limits are. I think it's good to have some margin, so I'm going to continue to aim for ~10 deg clearance.

Note: All of my bevel down bench planes have a 45º bedding. All of my relief angles discussed are in relation to this bed angle.

It seems Normand has test results which indicate the 10º clearance angle will have diminishing effectiveness sooner than a 20º clearance angle. Are you saying you may have to hone the blade more often but each time is removing less metal than those of us with bevels starting with more clearance?

I'm not sure what point you are trying to make, but it has not sold me on changing my bevel angles for bevel down planes.

From your post #39 in this thread:

If you look at Kees' diagrams (and many others out there) what you actually see is a ~flat wear patch developing behind the edge. It's more "an ever-growing patch of zero clearance" than "reduced clearance". That's why I'm not entirely sold on the link between the initial clearance angle and problems with wear bevel. That flat spot is going to form no matter what angle you start at, so the real question is "does it form faster with lower initial clearance".

I believe the answer is yes, with a lower clearance angle the wear formation affects the cutting action with less work output.

From the "Review of Cap Iron Study:"

The back, or beveled, surface shows a wear profile with a flat surface developed behind the tip at an angle of about 10 degrees, corresponding to the relief angle for the blade in this experiment. This wear is the result of the wood surface rubbing against the beveled side of the blade. It should be noted that this wear negates the relief angle of the blade. It will be shown that this wear surface pushes the blade away from the wood surface.

I have had my Veritas MkII Power Sharpening System for over 10 years. The instruction book that came with it had some discussion on bevel angles. My recollection is the comments on a 35º bevel angle was prone to skipping out of the work. I do not know where the manual is currently. Most likely it is packed away somewhere. If it is found in the near future I will post the exact wording.

In summary, my opinion is a 10º relief/clearance angle is not going to save any appreciable amount of blade metal. You will have to come up with something more convincing to get me to believe, "that extra clearance is nothing more than wasted blade life."

jtk