lets explore belt sander sharpening

[hockenbery]

Bill,
The belt sander will produce a flat bevel
The wheels will in most cases leave a concave bevel

The con cavity of the wheel will leave a slightly more acute angle than the flat bevel and thus a slightly sharper tool.

Al

 

[AlanZ]

Al,

Doesn't that really only apply to a skew (if it has any real effect at all)

Gouges are sharpened to a pretty wide angle.

 

[Jake_Debski]

Bill,
The belt sander will produce a flat bevel
The wheels will in most cases leave a concave bevel

The con cavity of the wheel will leave a slightly more acute angle than the flat bevel and thus a slightly sharper tool.

Al

Al, Just for the sake of discussion, wouldn't or couldn't the jig, platform, etc. be set to compensate for any slight variation in the bevel angle?

jake

 

[AlanZ]

I also don't know if I would characterize a concave grind as a "slightly sharper" tool.

It does provide a slightly thinner, but structurally less supported edge.

Sharpness has to do with the intersection of the two planes, and how rounded over the intersection is.

You can make a 90 degree metal edge that will slice into your finger.

Let's think about it this way:

If one contends that a 8" concave grind makes a sharper edge than a flat grind (or a 10" wheel), then isn't is reasonable to assume that a 6" wheel would make even a sharper edge?

How about a 4" wheel? Even smaller wheels?

So, all I'm saying is that the type of grind concave, flat, convex has little bearing on the effective sharpness of the tool.

Tools need to be sharpened to whatever shape and thickness that is appropriate to the task at hand. An axe and a scalpel are both sharpened to do their job, and each edge would be miserable at the other's job.

 

[Jerry Hall]

I think of sharpness as

two equally smooth intersecting surfaces. The edge can only be as sharp as the least smooth surface. This is true for any cutting tool, bench chisels and turning gouges, axes, knives, scissors, swords. It is true with speech also. Ten "attaboy's" are offset by one "sh**"

While there is disagreement about how sharp (80, 100,...600) a turning tool needs to be, there can be no disagreement with the basic principle of sharp being defined by the least smooth surface. So the flute and the bevel work together in a gouge.

So if you want to improve a surface that is ground to 80 grit VVVVVV that intersects with a flute that is much smoother vvvvvv, then honing is one way to do it. If you do this by hand honing (Alan Lacer's preference and now mine) then you must practically have a hollow grind upon which to bridge the honing stone. That makes it easy to sharpen without having to remove much material, and to index the hone across two points, reliably polishing the cutting edge without round over.

I hone because it produces a better edge and a better surface on the turning. And it saves me many trips to the grinder. I only go to the grinder when the polished part of the bevel approaches about 1/16th inch wide. You can easily see the VVVVV of an 80 grit cut on the surface. A honed gouge creates a cut surface that is visibly superior. It is important to lightly hone the flute as well so that you are insured of comparably smooth intersecting surfaces.

A flat plattan sander with a fairly high grit can approximate the smoothness of the flute of a well made tool and be a reasonable outcome. Sanding at 80 grit is the worst outcome because you cannot improve the surface by hand honing, but possibly with a jig and power honing wheel. But that seems silly to me.

To another point. Yes, honing in a sense creates a more acute secondary bevel. If you don't want that result then make the initial grind to a slightly steeper angle. But I thinks that is a very negligible matter.

That's my story and I am sticking to it 🙂

Jerry