Edge bevel and geometry

[Alain M-D]

Hi !
Until now I made only knives with hollow grind.
Now I make my first convex grind blade, and I have some questions:

1- So that I can note, I do not think that they useful to add a secondary edge (edge bevel) on a convex grind blade? Yes or no ?

2- For the hollow grind, it seems necessary to make a edge bevel. Which is the good thickness of the blade before the edge bevel? (0.030? 0.020?)

3- Is the flat grind is like the hollow grind (with a edge bevel, and which thickness?)

4- For my hollow grind, I do them with the slack part of the belt, that gives a nice convex edge. Is it more difficult to sharpen for the customers ? Is this the best method? Convex or flat edge ???

Thanks !
Alain M-D

 

[Alain M-D]

Nobody have an idea on this subject ???

Alain

 

[Mike Hull]

Alain, for the average knife user, a convex edge is hard to sharpen. Years ago, Buck knives was putting a convex edge on the ever popular 110. Everyone said how sharp they were. Shortly after, they were all saying how hard they were to sharpen, many said they were impossible to sharpen. Many blamed the stainless Buck was using for the blades(440C). Buck went back to beveled edges and all was well. Many people still say stainless is no good, because of experiences like that, years ago.
I hollow grind my blades, and on most, I put on a beveled edge. I do it on the vertical platen, buff the wire edge off with a felt wheel, loaded with green SS compound. They come out very sharp. There are others though, that I sharpen on the same platen, but just below the platen, between it and the bottom wheel. It is a slack part of the belt, but is very tight. I finish the same way. These also come out very sharp. I usually do the latter on my own knives.
I know there are folks here who will say, it's no problem to sharpen a convex edge, and they are right, if you know how. For others though, it is a hardship, unless you want to show them the proper way to do it.

 

[Hagar]

the thickness at the edge for the secondary bevel wether hollow, flat, or convex ground, will depend on the use of the knife (chopping you want thicker, slicing thinner/ and your preference.
my knives are usually flat ground with a slight convex. Usually the thickest I go is .020 the thinnest .010 (before heat teating).
i had one customer who insisted on .064

 

[Alain M-D]

Thanks Hagar and Mike !

Do you make a secondary bevel on a convex grind blade or do you sand
until you obtain a good sharp edge ?

Mike:
I imagine that if I want to sell my knives to everybody, is better to not have
a too convex edge (if they want to be able the sharpen the knife with a
Lansky sharpening system or a diamond sharpener. Or perhaps that I can
do it less convex, on a slack belt not too slack?

And if want to make a non-convex edge, which is the best technique todo it ?
(on the slack belt with more tension, not too slack, platten, contact wheel ?)
What do you think about paper wheel kit ?

Hagar:
I leave about 0.030 before the heat treat, after a clean and
sand and I obtain about 0.015 - 0.020 before putting my edge bevel...
I assume I am ok. for medium size knives (8"-10" ) ?

Thanks !

Alain M-D

 

[Mike Hull]

Alain, I do mine on a platen with the belt running at about 10-12%, if you have VS. I do this edge down, and it is easy to see the angle, which will depend on the use. Kitchen knives at about10-15%, heavier use knives 18-whatever. I start with a used 120 grit, making a couple of passes per side, until I get the wire edge, I then switch to a 320 grit and repeat the process. From there I go to the buffer and run the blade across a felt wheel loaded with green SS compound, wire edge side first(edge down), at a 45degree angle(lightly). I make one more pass at a slightly higher angle, and repeat on the other side. For convex, I do it basically the same except I use the slack portion of the belt right below my platen.
Everybody seems to have their own way to sharpen, and as long as it works, what the heck. This just happens to work for me.

Edited to add; I have never used the paper wheel kit. I have heard some people say it works great.

 

[itrade]

I agree with Mike on the flat grind for customers. Another thing I found using the paper wheels is you get a slightly hollow edge bevel. It is extremely sharp, but it doesn't last long.


I'm one of those that has a terrible time sharpening with anything other than my method - I'm still trying. Regarding paper wheels,
I sharpen on the platen, then use the grit-less paper wheel to nock off the burr.

I can't get anything else to work for burr nocking. I've tried corkbelts, buffing wheel (don't have a felt one like you Mike), leather strop mounted on wood with green compound, increasing the angle with an A6 belt, paper over glass, ....

So it's the paper wheel to remove the burr and platen to sharpen.


Steve


FWIW I like to set up the platen like this (notice my CUSTOM FRINK PLATEN with the adjustment groove, he made it just for me ):

Then run the belt backwards. With the edge away from me, I hold the blade level and work it that way. Mike, you can see the angle with the edge down, I can't. Personally, I think that shows a better eye on your part. This method just works for me.