Sharpening Jointer knives

[grice]

I have the tools needed to sharpen jointer knives with either:

1) a flat surface 2) a hollow ground surface

Which type of grind would YOU choose and why?

Gary

[WConner]

I think hollow grinding would weaken the point too much in this application.

Walt Conner

[Doug Miller]

I'd choose whichever one I could do faster. For me, that's hollow-ground, because I already have a Tormek grinder with the appropriate jigs.

[SWDeveloper]

I use a waterstone and a jig. A hollow ground surface does not make sense.

[Doug Miller]

You must be using a *very* tiny grinding wheel. :-)

My jointer knives are ground at an angle such that the bevel measures about

0.16" wide. I hollow-grind them on a Tormek grinder with a 10"-diameter wheel. The difference between the hollow-ground curve and a straight line calculates to 0.00064" maximum.

I haven't noticed any particular problems with weak edges...

[Leon]

I believe hollow ground would be a wasted effort. The grind would be on the wrong side of the knife edge to be of any value. Typically the hollow grind is on the side of the edge that cuts away the shavings.

[Anonymous]

Hollow-grinding would probably give a better finish, for a much shorter period of time. Hollow-grinding removes much of the support directly behind the cutting edge, making it much more vulnerable to dulling quickly.

[Dave Jackson]

I don't believe there would be any added benefit of flat vs. hollow, so choose the one that is the easiest and most repeatable for you. Personally, I use a Tormek and jig (which produces a slight hollow grind) and have been happy with that. --dave

[Scott Lurndal]

The sole purpose of a hollow grind is to make honing faster because one doesn't need to remove the material in the hollow. A hollow grind makes little difference to cutting performance.

scott

[WConner]

" Hollow-grinding removes much of the support directly behind the cutting edge, making it much more vulnerable to dulling quickly."

You said what I was trying to but much better.

Walt Conner

[Leon]

Scott, you do not know what you are talking about. If you want to speed up honing an edge simply increase the angel of the micro bevel on the edge. A hollow grind creates a concave surface below the cutting edge. The hollow spot reduces friction against the shaving after it has been cut and that air gap makes the cut easier and smoother. Some old style circle saw blades were hollow ground for smoother cuts. That in no way helped to hone teeth. My pocket knife is hollow ground about

1/16" below the cutting edge. I would have to remove 1/16" of steel to make honing the edge easier or to reach the beginning of the hollow grind.

Do some studying.

[Leon]

At the risk of wasting my time , I gathered information for you again. Study or remain ignorant. I got this information from the top of a Google search.

Blade Grinds

- The Hollow Grind

The hollow grind is done by taking two concave scoops out of the side of the blade. Many production companies use this grind, because it's easier to design machines to do it. But many custom makers grind this way as well. Its great advantage is that the edge is extraordinarily thin, and thin edges slice better. The disadvantage is that the thinner the edge, the weaker it is. Hollow ground edges can chip or roll over in harder use. And the hollow ground edge can't penetrate too far for food-type chopping, because the edge gets non-linearly thicker as it nears the spine.

For designs where slicing is important, but the slice doesn't need to go too deep, this grind is an excellent choice. Many hunting knives are hollow ground, because field dressing is often best done with a knife that slices exceptionally well through soft tissues. Unfortunately, if you hit a bone, you can chip the edge, so the flat grind (see below) is also used often.

Another advantage of the hollow ground knife, at least at the beginning, is ease of sharpening. Most hollow grinds thicken slightly towards the edge. That means that as you sharpen (at least at first), the blade gets thinner and easier to sharpen. After this, however, the blade begins thickening non-linearly and sharpening will become more difficult.

The ultimate push cutter, the straight razor, is usually hollow ground.

[Anonymous]

Pretty much an expanded version of what I said .. .. .. but he ignored me too !! !! !!

hehehehe !!

[George]

Since either will be produced under machine power, makes no time or convenience difference if hollow or flat. Takes longer to set up a grinder and jig than to freshen the blades with it. Other than laying the knife flat on it to clear any wire edge (which will clear anyway), a stone is superfluous.

So why not take the tad bit extra durability in the flat-ground edge. Unless you spent your bucks for a Tormek, of course.

[Doug Miller]

Well, yeah, but on a jointer knife, the ground edge is so narrow that it doesn't make any difference at all.

[Leon]

Agreed, which is basically what I said. Basically the hollow grind on the jointer knife would not be utilized at all. But then there was the comment that the sole purpose of the hollow grind was speed honing, which was a shoot from the hip BS statement.