>With a bevel down plane the back of the blade faces the work. Therefore the bevel angle shouldn't matter much since it lies behind the action.
Right?
What if we increased the bevel angle to match the throat angle, say 45 degrees for a standard smoother. It seems to me that the resulting edge should be much stronger with that extra metal behind the blade edge...
I've read Leonard Lee's sharpening book, where he explains the rationale for the relief angle (as fibers are cut they spring up momentarily), but somehow I'm not totally convinced... And if we skew the plane in use, wouldn't that rationale lose its relevance?
>the higher the angle the less sharp the edge is. and as you say the edge will hold up better. as usual they are all comprimises and you have to work out the onee you need and the ones you can sacrifice.
Would you say that a (say) 45 degree bevel is less sharp than a 25 degree bevel if both are honed equally on a 8000 waterstone? Or would you say that the latter just feels sharper because it has greater penetrative ability? Or are we splitting hairs?
The issue becomes more pertinent with Bevel Up planes, where high angle settings involve bevels of around 50 degrees. Is the BU blade "less sharp" than a Bevel Down blade in a plane with a frog angle of 50 degrees and a bevel of 25 degrees?
>One thing I've noticed, being as user of both styles of planes, is that blades with high bevels may resist chipping and roling edges better than blades with low bevel angles, but they lose their sharpness faster and tend to skate over the wood sooner. I think there's a balance between how much metal you want right behind the cutting edge (higher bevel=more metal) and how long you want a blade to hold its penetrating ability (lower bevel=more penetration). Maybe someone who knows more can comment.
As to Denis' question, you need a clearance angle otherwise your edge will be lifted off the wood. Skewing the blade doesn't change the clearance angle, only the planing angle (the top of the blade when you plane). As long as you have clearance you can do what you want, but I think the rule of the smallest possible bevel angle that holds up well is a good one to follow, i.e. the previous paragraph.
>Lower angles are generally for softer woods and higher angles are generally for tougher woods. If the angle is too low, the blade will bend and break. If the angle is too high, it makes the blade too hard to push. The best angle is the one which does not bend or break, holds its edge, and is sharp enough to cut quickly.
>How about if we hone a cutter with 179 degrees between the bevel and back?
:- ).
There is a point of diminishing returns....I think the senior Lee uses the term "keeness" of the edge to talk about what a very acute angle gets you versus "sharpness" of the edge which I'm assuming you take as the quality or smoothness of the meeting point between the bevel and back.
If you take a well honed sword or knife and the cutting edge planes meet at 10 degrees....it will slice your finger by just touching it. Say you refined the edge to 30,000 grit JIS. If you refine the same sword or knife to the same degree but this time the cutting edge planes meet at 45 degrees, you'll have to apply some pressure on the edge and/or move your finger along the edge to get it to cut you. yet they're both the same 'sharpness.'
As L. Lee states....there is a reason why razor blades have such acute angle. They don't need a lot of strength since shaving hair isn't nearly as tough as planing wood. Similarily, shaving hair requires the cutter to cut with minimal force or the hair will simply bend and deflect while the wood fibers tend not to do so even under the larger forces presented by a more obtuse cutter because the wood fibers are tied (lignum) together into a single unit while wiskers or leg hairs are stand-alones. You get 'razor burn' from using a less than sharp razor blade because it pulls and rips the hair rather than cutting....
I guess another way to think about it is that edge failure results in a more obtuse angle. Rather than the cutter being beveled at 30 degrees....if the edge fails, it may be more like 90 degrees down where the actuall cutting takes place.
Coupla thoughts, and talking about bevel down planes for the moment. If you have ever had to bear down on the plane to keep it in the cut, you were experiencing the loss of relief angle.
In the limit, the plane just won't plane--it'll bounce off the work before the edge can engage. But leading up to that point, another thing is happening. I accept the argument about fibres springing back (particularly in soft woods, not so much hard maple). But in addition--and this is really well brought out by Brent Beach at his website--the dulling of the blade is causing loss of relief, by creating its own little flat place behind the edge on the bevel side, due to metal loss. As Brent points out, you can think your blade is dulling quickly, when what is really happening is that you're losing clearance.
Rounding the bevel during sharpening can accelerate this loss of relief due to wear (dulling). The cost of rounding is loss of clearance. Due to the geometry of the situation, minor losses of relief become more significant for bevel down planes bedded at low angles--such as Japanese planes, often bedded around 40-43 degrees. I think it is for this reason that many Japanese plane users are extremely attuned to the flatness of their sharpened bevels. Because losing several degrees of clearance due to bevel rounding is significant when the plane is bedded at 40 degrees. This is also why really fine steel is imperative in the Japanese situation--the blade has to be effective and non-chipping at fairly low included angles, often 25 degrees. Compare this with Steve Elliott's observation that he had to sharpen one of his A2 blades (from a very well-known maker) at 32 degrees before he could get away from unacceptable chipping, and this was on cherry, IIRC!
You spoke of bevel-up planes. It strikes me that a possible advantage of a bevel-up plane is that it has a built in clearance angle equal to whatever the bedding angle is. Perhaps other factors are at play, and comparing clearance between bevel-up and bevel-down is more complicated than this, but it does seem worth some discussion.
>So how does the angle of cut change? A bevel down plane cuts at whatever the frog angle is ie 45 degree's Thank got the heat wave finally subsided for last 2 days.
>Does the size of the micro bevel effect the performance? I try to keep mine very small in order to speed up sharpening but also think it makes for a keener edge.
I'm not at all familiar with floats so I'll leave that alone. I do use scrapers...both burnished and not.
One significant difference is the shavings between a scraper and a hand plane. Scraper shavings start somewhere in the 0.001" (I've never actually measured so I'm just tossing out numbers as reference or comparative points) range and generally go thinner. Plane shavings are considered by most to start in the many mils...say 0.006" range and go thinner and 0.001" is considered a decent minimum thickness for a smoother plane.
The thickness of a shaving affects the resistance to cutting just as does the angle of the cutter edge. Hence....going to a more obtuse angle but a thinner shaving is similar to going to a more acute angle but a thicker shaving. Yes?
I'd gather you'd never think to shave your legs with a 90 degree angle scraper. At least I'd NEVER consider shaving my beard with one. hahahahhahahahahahaaaaa. :- )
>"You spoke of bevel-up planes. It strikes me that a possible advantage of a bevel-up plane is that it has a built in clearance angle equal to whatever the bedding angle is. Perhaps other factors are at play, and comparing clearance between bevel-up and bevel-down is more complicated than this, but it does seem worth some discussion"
Something about pictures/micrographs showing that BOTH sides of the cutter wore during use. That is, for the bevel-down planes, the beveled part of the iron definitely showed wear at the cutting edge but so do the back of the iron.
Given the above observations from Brent, it seems likely to me that the back of a bevel-up iron will wear similar to the bevel of a bevel-down iron and the bevel of a bevel-up plane would wear similar to the back of a bevel-down iron. Hence.....neither affect the wear of the iron much.
>We're kinda diverting from the main focus of Denis' message, but it is mildly intersting to me nonetheless. I will gladly continue to read this sub-topic if others pursue it, but will stop with this.
How often do you need to renew the edge on a scraper vs. a plane for a given amount of work?
It may be true (I don't know) that one can sharpen a 80 to 90 degree angle to the same degree of keeness of a 25 or 30 degree angle. But in the practical world in which we work, a scraper will not retain a functional edge as long.
So while it may be measurably similar. Practically there is a world of difference. I certainly would not desire to scrape all my work to thickness. Horribly ineffecient, that would be.
>Good point, Jim. I was talking about hand held cutters, so the angle of cut changes all over the place, with both the edge angle and the hand position relative to the thing being cut.
>The thickness of a shaving affects the resistance to cutting just as does the angle of the cutter edge. Hence....going to a more obtuse angle but a thinner shaving is similar to going to a more acute angle but a thicker shaving. Yes?
I don't know, Tim, logically it sounds good; but I haven't done any comparative studies. And, no, I wouldn't attempt leg shaving with a plane, float, or scraper, regardless of edge angle. :)
>Dennis ... I often wondered the same thing and none of the explanations I've read convinced me of their "rightness".
I routinely grind my bevel down irons at 30-33 degrees. I tried several angles with a Hock iron in an old, well tuned Bailey #5 and found that I could go to 38-39 degrees before I started having trouble in soft and semi-soft woods and 35 degrees was pretty much the maximum in the harder woods - the iron started cutting eratically at higher angles; I don't know why, nor do I have a theory.
I also tried multiple angle with an old Stanley iron and found I got somewhat better life out of a single honing and a slight improvement in chatter.
I know I didn't answer your question but I try not to miss an opportunity to further confuse and obfuscate an issue .... :-) rj
>just use a plane. Set it for a certain depth and plane. Then set it for a finer cut and plance. Then set it for a deep cut and plane.
Which set up did you have to use the most force to push the plane? And remember to leave the mouth open so clogging doesn't become an issue.
You can do similar with chisels. When I'm cleaning up the waste on the bottom of dovetail sockets I've coped, I can chop the waste using a hammer or I can pare the waste by using body weight. I cannot force the chisel through the entire waste by using my body weight alone. I have to take several/many fine shavings but I can slam the chisel through that thick bit of waste with a hefty hammer blow.
>I asked the same question of one of my recent instructors.
He said that inevitably the edge wears back a bit during use. As that happens, a greater angle will get blunt much faster.
Thought of another way... if you sharpen one blade to 20 degrees, and one to 45, and then grind back 1/32 or 1/16, the new facet will be much larger on the blade ground at 45, because as you come back from the edge, the blade gets thicker, faster.
Going back to a blade in use, even though the process is happening at a microscopic level, a more acute angle will hold its sharpness longer, and be easier to push.
I'm not sure how to argue the float and scraper point... My own floats look to be more like 60 than 90, but maybe yours are different.
But on scrapers, even if the edge is ground, filed, and polished to a perfect 90, I think there will be some edge distortion in use. When you use a scraper, you bend it, just a little bit. That will stretch the leading edge of the newly polished face. So the new planar surface is arch shaped, or it's not planar, and the leading edge is getting pulled out of plane to a an angle that's finer than 90. One effect of the distortion if the edge is still planar though, is that the outer edge will now have a greater length than the inner edge. They're now essentially concentric arcs, which will naturally have different circumferences.
Which is all fine and good if the scraper remains at that arc. But once the scraper is flattened, or allowed to slacken a little bit, or flattens a little bit when it's pressed into the wood, the difference in circumference has to go somewhere. My guess is that the newly stretched steel just goes... out. And at that microscopic level, it's no longer 90 degrees. It's probably much finer.
Of course, that could all be BS... I'm pulling all of this straight out of my backside at the moment, but hte math al makes sense, and even if it's been ground at a perfect 90 and polished, I've never seen anyone use a scraper by holding it flat, unless they're using it to take off glue.
>James, I have no serious disagreement with what you said; however, none of this affects the achievable sharpness of an edge, regardless of what happens to it during use.
As to scraper blades, the edge starts out sharp regardless of how it wears, whether I apply it at 90° or 45°.
