Primary and secondary bevels

[C Craft]

So here is where this starts for myself! I always ground down to the near dimes thickness mark with my blades, HT and the do a secondary bevel after HT.

So this is my train of thought for bringing this up for discussion!! I have been watching, listening, and learning, of late and I am about to try something new!

I am going to try grinding my blades after HT. The consensus seems to be that it is easier!! Also it eliminates some of the problems with missing the dimes thickness theory!! So here is where the actual question comes in!!
```````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````

If I do my grinds after HT, and I grind the bevel in and polish to finish. Why do a secondary bevel???

Lets say I do a hollow grind, ( I was looking at a hollow grind somebody had posted a pic of, when I had this revelation) and pull it down to a finished first bevel!! Why do a secondary bevel???

Once that first bevel dulls and you have to re-sharpen you will automatically create that secondary bevel when re-sharpening!!!

Or will having a primary bevel only, make that bevel be easy to dull, and/or other problems I am not forseeing??

So I open this for discussion and lets be nice ladies and gentlemen!!

 

[KenH]

Cliff, I don't think primary/secondary bevels have a factor in grinding pre or post HT. I'd think the decision would be more based on use of knife. i.e. for a kitchen knife (slicing chef, paring, etc) I grind primary bevel to around .010" to .015" edge (FFG) post HT. If I wished to grind pre HT I'd grind the same way with a FFG but stop with the fabled "dimes thick" edge, do HT, then finish the FFG down to almost the desired edge (maybe .007" to .010" or so). I put the finish edge on with a slack belt on the 2x72 grinder running in reverse. This puts a bit of a convex edge. Some folks will even put the convex edge from .040" and say it slices just fine with a FFG.

Come to think of it, that's about the way I'd do a camp knife also, but put the convex edge from the .040" so there would be more strength for chopping. OR - for a kitchen knife that's to be used for chopping (bones, frozen meats, etc).

When you're sharpening from the .010" edge, there's just almost no secondary bevel anyway.

Good luck, just my opinions. Looking forward to reading other comments.

 

[Drew Riley]

I agree with Ken that pre/post heat treat grinding is somewhat of a different issue than "zero grind" bevels, or having a secondary bevel.

You can always grind your primary bevel to a zero point (as you'll see in a typical Scandinavian, or "Scandi" ground knife), but depending on the steel and the heat treat, while this will no doubt give a very sharp edge, it may not be very strong. There's a reason that Scandi ground knives, for instance, never go all the way to the spine, but try to maintain an angle of at least 11 degrees per side, or 22 degrees inclusive. If you go much thinner than that, the edge doesn't have very much material behind it to support it, and you start to get edge deformation much more quickly.

When you add the secondary bevel, this allows much more material/support behind the edge, which will invariably last longer under use.

 

[C Craft]

Sometimes it is good to have a sounding board. so to speak!! I am hearing my moment of thought was more a moment of a brain-fart so to speak!!

I guess I just got carried away with the prospect of grinding bevels after the HT would open up a new world. I jumped in an amazing leap right overtop of the real reasons for the secondary bevel!! Strength being a big factor.

For the record I have never ground a knife with nothing but a primary. The blade I said I was looking at when this great thought hit me was a hollow ground! From there my mind jumped to sharpening it!! That is where the idea came from eliminating a secondary bevel!!

I guess I was looking at re-inveting the knife and that big revelation was just a left over from the head ache I have had all weekend off and on!!



Anyway sharpening is where this idea was supposed to be headed. So let me take this thought process one more step. The average person doesn't know how to sharpen a knife and the thought of doing away with a secondary bevel was a thought that I figured might help this, or not!

I have had folks that come to me and ask about sharpening this!! Nine out ten times you look at it the blade they just handed you and you will see why they can't get the knife sharp!! You will see a series of swirls of where the stone or in worst case scenario the grinder, hit up on to the secondary bevel of the blade.
If it is a stainless steel of the hard to sharpen variety I will usually tell them that is part of their problem. However the marks or swirls show the story! The made 10 passes on a stone, and only two of those were made at the same angle. That is where most folks fail at sharpening a blade. I will pull out one of my stones that I figure they can't destroy and tell them to show me how they sharpen!! I will then show them the proper angle they are looking for as they make that pass on the stone!!!

Most time within a few strokes I will see them being all over the place and while in the middle of one of those wild strokes, I will try and stop their hand while in the middle of that stroke!! Look at where you hand is now! You made two stokes correctly and then you made the next three at a different angle. You basically destroyed the first two stokes you made that were at the correct angle, or at the very least you did not fortify (for lack of a better term) those two correct strokes. The next three are showing in these marks up here on the secondary bevel!! I get them to try and be consistent at that sharpening angle. Then I sharpen it for them and let them watch me!! Their has been a couple that I pull out the Lansky sharpener for and say this is a consistent angle!!

So I guess I was just looking for an idea that might help the sharpening process and re-inventing the knife probably wouldn't help that!! So thanks guys for indulging me with that hair brained thought!!

 

[C Craft]

Thanks David, I have had to put my actual making on the side burner again as of late. The wife's illness continues to cause problems for her! So I have as yet not been able to try a grind post HT!

could be I was just tired the other night and what seemed to be a revelation was nothing more than. a clouded thought!!

I do think it will if nothing else, grinding post HT should stop some of the warpage problems I have had in the past!!!