Clearance in BD plane

[Brian Holcombe]

Jim Exactly, It comes in handy on occasion. I've turned over chisels and saws without regret but the shipping prices make it fairly expensive to turn over larger things.

Back to clearance angle, I've only found it to be an issue with a 38 degree bed and attempting to take super thin shavings. Not something I do except on show faces so I don't mind sharpening often.

Steve that's where I am at as well, I really only use the Jack, try and LN 4 on the regular. I'll probably make my LN 7 redundant soon enough I'm tired of shooting with a 10lb plane, I will replace it with a long Kanna.

I also tend to stick with steel that can all be sharpened by the same stones as well.... Or at least I'm heading in that direction.

[Patrick Chase]

a

Steve Elliot looked at the formation of the lower wear bevel, that is the rounded bulge just behind the edge at the underside of the blade. The part touching the wood. This lower wear bevel tends to lift the edge out of the wood, ultimately leading to the feeling that you must sharpen again. Populair believe is that the roundness of the very tip of the edge makes the unsharpness, but Steve's test proves that's not true. The tip quickly looses its very sharp tip and after that the radius of the tip doesn't change much until the edge becomes very very blunt, way beyond fine cabinet making standards. http://bladetest.infillplane.com/htm..._profiles.html

So, the wear bevel at the clearance side of the blade is what makes the tool feel dull. It would be reasonable to think there is a correlation between clearance angle and the formation of this lower wear bevel. But I don't know of any study specifically adressing this issue. I did stumble across something though when I did my tests to compare high cutting angles to chipbreakers. The article is here: http://planetuning.infillplane.com/h...pbreakers.html

The second part of this study was about the wear behaviour. I meassured the horizontal force (pushing the plane) and the vertical force (the pressure of the edge against the shaving) Especially the vertical force is interesting in this case because it represents the effect of this wear bevel. When the blade is sharp this force is ideally negative, meaning the edge is pulled into the wood. Wear makes it less negative or even positive, meaning the edge is more and more pushed out of the wood, neccessitating us to press harder on top of the plane (or sharpen the blade).

Attachment 337878

Now, I first did my tests with a 60 degree plane with only a 15 degree clearance angle. I saw that the vertical force increased faster then my 45 degree planes. Don Willans complained about this, saying that was not enough clearance. I repeated the test with a 30 degree clearance angle, and behold, the wear rate was a lot better! (Still, not quite as good as the chipbreaker plane of course ;-))

My conclusion: High cutting angles and low clearance angle are not an ideal combination. This of course still prooves not much about planes with a standard cutting angle.

I can buy this. At 60 deg cutting angle you already have a reasonably beefy edge even with the higher clearance, so you may be seeing diminishing returns in terms of edge life from increased tip angle, and at that point other concerns will dominate. FWIW I usually don't go higher than 40 deg (or even 35 most of the time) on my BD blades for that reason, even when used in planes with high bed angles - it just isn't worth the hassle.

Note however that the low-clearance configuration *started* with higher cutting force than the high-clearance one, and the difference between the two was fairly constant after the first 25 m of cutting. To me that suggests that wear bevel formation is not the sole cause (and probably not even the principal cause) of the difference. If it were wear bevel related they should have started at the same force, and the low-clearance configuration should get worse with increasing distance. Also note that even at 100m the increase in cutting force is on the order of 20% - Even if that were due entirely to wear bevel formation I'd personally consider it a good tradeoff in exchange for the better chip resistance etc from higher tip angle.

To be clear, I don't disagree that wear bevels form and that they cause the edge profile to change as in the article you linked. What I'm not convinced of is the link to clearance angle. It isn't unequivocally supported by your data for the reason given above. Also, if you think about the mechanics of clearance-face wear, it's fairly likely that it may initially be worse at *high* clearance angles (think about the normal pressure on the wear patch as it starts to grow).

EDIT: Thinking about this some more, it makes sense that high-angle blades would require more initial clearance. The cutting mechanics have more of a "scraping" character and as a result the component of the cutting force that compresses the wood will be higher. More compression -> more rebound -> requires more initial clearance. That explanation seems more consistent with your data (particularly the fact that the 15 deg configuration required higher cutting force at the start, before any wear had occurred) than is wear bevel formation.

[Patrick Chase]

ROFL... Seriously man, you have far too many tools if you can't keep track of them without a spreadsheet.

I don't track tools, I track blades. I don't like to break for sharpening, so I have a fair number of spare blades. It used to be that I only had to track the BU ones since all the BD were either identical or different in obvious ways (camber etc). That changed when I started messing with bed angles.

[Patrick Chase]

Yes, a strop was used but very lightly with the blade in a sharpening guide.

That being the case the bevel at the very tip (the first few tenths of an mm that Kees' diagrams focus upon) is likely a couple deg more than you think, and your disastrous results at "9 deg" start to make much more sense.

The fact that you strop with a guide is irrelevant. Dubbing happens because of the compliance of the strop material itself, and that happens no matter how you constrain the blade. The conformance of the leather is roughly proportional to sqrt(force), so stropping lightly doesn't help as much as most people think.

To be clear I don't think there's any problem with stropping, but I think that if you strop then you have to add some clearance to allow for micro-scale edge rounding in exactly the same place where any "wear bevel" would subsequently develop.

[Patrick Chase]

Just to be clear, I too have a lot of bench planes. Partly it's an occupational hazard, but I also have Stanleys 3-7, a bunch of old woodies, and if someone offered me a mint Bedrock right now, I wouldn't say no. The issue, though, is not how many planes you own, but how many do you use day in, day out. On that, I'm pretty sure we agree.

I would never claim that my approach is optimal :-)

[george wilson]

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.

[Brian Holcombe]

George I tend to agree. Steve's thread on gouge marks was Definetly one of the more interesting as of late. I've been considering starting my threads with the design posted first to have that become a topic in and of itself before kicking off the technical aspect of doing.

[Normand Leblanc]

Hummm...You could be right Patrick. I am going to have to figure out another test it seems.
It's quite possible that a RA of 12 degree would become 10 or 11 after stropping but, to invalidate the results that I got, it would require much more dubbing than that. I'm going to check that this week and let you know.

[Patrick Chase]

We know there must be some clearance angle behind the edge of the blade. If close attention is paid to the video by professors Kato and Kawai it is clearly seen there is some rebound in the wood after the edge passes.

As the edge wears the clearance angle is reduced.

I think everybody agrees with the first assertion. Wood is compressible, and the downward component of the cutting force compresses it. You need some clearance to accomodate the resulting rebound, and the only open question is "how much". I think that's why I needed more clearance in Alder than in less compressible woods BTW.

I don't think that wear bevel formation is as simple as reduced clearance angle. 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".

[Kees Heiden]

The wear patch increases, not only in length, but also in height. The changing vertical force, measured by lots of scientists, is another sign that this happens. It removes the clearance, so it is not such a far fetched idea that the initial clearance plays a role too. But I don't know how much.

BTW, this being the handtool forum makes it not so strange that we discuss handtool topics.

[Normand Leblanc]

My finest stone is an hard Arkansas and, with that stone and a freshly sharpened blade, my Stanley 5-1/4 don't even make a single cut using only his own weight (goes to show that the stropping is really achieving something). This plane is my lightiest one. For a new test I had to use a heavier plane and it was a Record no.5 with an old Record blade. That blade performed much better than a Stanley blade in another study (60% better than Stanley).

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

So, you were right Patrick. Using the strop was changing the geometry at the tip.

It's interesting to see that 25 degrees is the best angle but the fact that I'm using BC Fir, a soft wood, must help for a low sharpening angle. I do not pretend that this test if perfect but it's giving a clear direction.

[Kees Heiden]

Nice work Norman.

What kind of shavings are you looking for? Just any kind of shaving or real full length and over what length? From your round numbers I understand that it takes a bit of judgement to decide wheter a shaving ios good enough or not.

And indeed I think in pine everything is a bit mellower then in oak for example, but it is much harder to get the plane taking an oak shaving spontaneously, then a pine shaving.

[James Waldron]

George I tend to agree. Steve's thread on gouge marks was Definetly one of the more interesting as of late. I've been considering starting my threads with the design posted first to have that become a topic in and of itself before kicking off the technical aspect of doing.

Please do! And everyone else too! Formal drawings or napkin sketching from the local pub, a look at where you're headed makes much more sense of the joinery you're cutting. And, as well, we all can learn about the choices to be made in the joinery to suit hand work (and why), since there are so many available choices.

[Normand Leblanc]

Kees,
That's what I like with this particular test is the "judgement" portion is kind of small.

Every five shavings the plane is placed in the middle of the board (the whole sole is supported) then I push it very slowly by the sole behind the handle. It is very easy to see if the blade slide or bite. Sometimes I can get an "in between". In this case, what I have done is, take another shaving (like with a no.8 to get as flat a surface as possible), make sure there is no debris and try again. If it's again an "in between", the test is stopped. Only full width shaving are considered ok. There is no length, it bites or not, 1/2" is plenty to make the call.

[Kees Heiden]

That's very interesting! I didn't understand you were taking normal full length shavings first, then do a test without any weight.

You should write this down in an as complete matter as possible and then we could see if we could put it somewhere for reference.

PS: and maybe you should repeat the test, just to be sure.