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+-- Thread: Flattening the back (/showthread.php?tid=7353606)
RE: Flattening the back - hbmcc - 03-22-2020
"But a butcher steels his edge because it rolls and it needs to be straightened so that it will cut. A steel does not sharpen just straightens."
I was taught that a long time ago. Simply looking at a ceramic "steel" is proof opposite. If a blade edge rolls it is poop worthless for the work it is expected to accomplish; even shaving. Again, check the above link to Science of Sharp. It's a trove of scientific information, not tales.
Steels work the same way stropping on a leather belt works.
Unless you were talking about scrapers. But I think that's another topic.
Bruce
Currently hiding from dirty breath, and fingers.......
RE: Flattening the back - wmickley - 03-22-2020
(03-18-2020, 12:32 PM)hbmcc Wrote: Everyone here will disagree with me, but I am finding two flat surfaces forming a wedge on a cutting tool easier to manage and control. They're even finer edged. I can dull an edge on an 8k stone too easily by farting around with stupid secondary angles.Yes, a chisel is a wedge, not just a knife on a stick. Flat bevels work somewhat better.
In the woodworking trade, sharpening is part of the work, not just something to get in the way of actual work. The mental aspects of sharpening, concentration and discipline are very important for quality work.
RE: Flattening the back - Timberwolf - 03-22-2020
(03-22-2020, 04:07 PM)tablesawtom Wrote: But a butcher steels his edge because it rolls and it needs to be straightened so that it will cut. A steel does not sharpen just straightens. So using Karl's theory after a person takes a few strokes with his plane it will have to taken it apart and sharpened, but not straightened because of roll, and the time frame would depend as you say on the hardness of the material being cut verses blade rockwell 'C".
The perfect cutting angle is 22 .5 degrees. But perfect cutting angle and a usable cutting angle are two different things. A paring knife is usually sharpened at a 25 degree included angle. And a plane blade sharpen at a 25 degree angle, it is the same angle as the knife. If you divide the plane angle in half and times the two you get an included angle of 25 degrees just like the knife. In othewards you get the same angle. 30 degree angle covered in next paragraph
I do not know what a butcher knife is sharpened at but Tormek instructions say 25 degrees for a paring knife and 40 degrees a hunting knife. The 40 degrees is because the edge need to be stronger, but to be stronger sharpness is sacrificed because the perfect angle is 22.5 and you can't have both. The same holds true with chisels and plane blades, the recommended angle for hardwood is 30 degrees, the edge is stronger and holds up better in hardwood but is not as sharp just stronger.
Toothing blades compared to straight blades is like comparing apples and oranges, different application much like a paring knife versus a hunting knife, both are knives, just the application is different..
So if meat (which is softer than wood ) will roll a cutting edge and the butcher has to steel the knife to keep the edge straight, what do you think hard wood verses soft wood will do to a cutting edge. When your plane blades starts to stop cutting usually it is removed and the edge is touched up on a stone and then the a couple of passes on the flat side and you are back in business. Note no real reshaping or hard cutting of the edge, just a touch up and you just did the same thing a butched did with his steel ( Rolled Edge Straightened) Toothed verses straight is application and angle is edge retaining ability.
ON a personal note: whether the micro scratches go parallel to the edge or perpendicular to the edge is really a moot point. For me it is easier for me to screw up an edge sharpening it with the scratch line going parallel to the cutting edge so I have them perpendicular.
And again grain doesn't change just as Ahill stated, plastic flow happens.
Tom
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First paragraph posted in the link above {page 3} seems to contradicts the "edge rolling" effect you mentioned...altho for the most part, I agree with your statement..A fine, polished steel straightens { re-aligns } the rolled edge as well as burnishes it,...Some butcher steels are grooved and some are smoothly polished..I have one of each and one is polished carbide..The "grooved" one will actually remove a tiny amount of stainless steel and probably carbon steel as well...
Page three..
"In Part 1 of this series, I showed that, contrary to myth, honing rods (including smooth honing steels) restore cutting efficacy by removing steel from the blade, not by “realigning the edge.”"
Buffing on a spinning leather wheel or endless belt using Linde "A" or chrome oxide both burnishes and sharpens and can produce the sharpest edges I have ever seen in more than 70yrs of experience. But it requires "perfect practice".....Whether it will stay sharp longer depends on the angle and the steel, but a sharp knife is a joy to use when carving wood and you know it when you achieve it.
RE: Flattening the back - adamcherubini - 03-23-2020
Sorry I brought up grains. I got a D in that class in college. I heard someone explain it once and I thought I understood that the kind of stress required to cut steel could also influence the bonds around individual grains, causing them to re-orient in line with the load. But whatever.
I can also see how a front to back honed edge could be stronger in bending, but also serrated. Since I skew most cuts, this could work differently for me. For a side honed edge, I could see how that edge could be smoother, but weaker in bending due to the cross wise scratches. But maybe the difference is minor on a well polished edge.
I guess my point is, this seems like one of those topics that you really can't BS about on a ww forum. Actually, sure we can. We just may not be right. And that's where I am.
Right now, with what I'm doing (general carpentry), I'm sharpening on DMT diasharp plates. But I guess I don't have the finest one because my edges are still a little ragged. Before purchasing another $60 plate, I tried varying the angles I hone in to no avail.