Sharpening---Which of these two practices is correct and why.

[Fred.Rowe]

When referencing the sharpening angle on a flat ground blade, what do you reference the sharpening angle too?

The drawing on the left shows the blade center line being used as the sharpening angle reference.

The drawing on the right shows the blade bevel being used as the sharpening angle reference.

To what surface of a blade do you reference the sharpening angle, the center line or the bevel surface? Which of the two is the accepted industry standard; or is there a standard?

This question does not apply to convex grinds.

Looking forward to hearing what you think, Fred

 

[Pete84]

Fred, I don't know about "industry standard", but I as a consumer and now a knife maker have always based my sharpening angle on the center line. Seems to give the true angle of sharpening, as you're not having to factor in the angle of the blade's grind, etc. Using the grind surface as a reference would, as I see it, yield a more obtuse edge angle when using a jig based system like Ep or others.

 

[sunshadow]

The centerline of the blade is the only truly relevant mark when deciding your included angle (22 degrees of included angle is 11 degrees from the centerline on each side) The time that the bevel surface is relevant is when doing a "scandi" grind where the edge is brought up as the bevel and you put the entire bevel surface on the stone (no separate edge bevel)

-Page

 

[richard j]

i guess that depends on the knife i'm sharpening and if there is any flats to go off of. thats why i tend to match up the existing angle when i sharpen unless the owner wants a thinner edge.

sometimes i have to tape a blade up when i sharpen it which hides any flats. i was sent a sidis which has very little ricasso area which was totally covered to protect the front of the handle and the rest of the blade. i just matched up the existing angle which felt pretty sharp to start with and worked up a burr. the knife was popping off what hairs i could find easily and the edge felt sharp.

 

[wolffbite]

It would seem to me that any angle NOT measured from the centre line wouldn't be correct (or at least the angle you intended). Based off the bevel surface you will end up with a larger inclusive final angle, and a more obtuse edge.

 

[Rick Marchand]

double tap.

 

[Rick Marchand]

It all leads back to a center reference... it has to. It is everything AFTER the intitial intersection of two angles(the edge) that dictates performance. A "sharp" edge is only the tip(pun intended) of the iceberg. I can sharpen a 90deg angle to shave hair... try slicing a tomato with it....

 

[Stacy E. Apelt - Bladesmith]

The measurment of the opposite angle in a triangle is refferenced to the base and thus to the altitude (height)....which is the center-line.

 

[Fred.Rowe]

This thread was posted to inspire discourse, not come to some final conclusion about grinding edges. I don't think there is a better way to improve what we do, than getting input from other makers interested in the craft.


Ten years, working as a surveyor along with 30 years building and fabricating stairways, has influenced me as a knife maker. I always think of knives in terms of degrees of angle. The pitch of the tang, the line of the spine and the grind of the bevels relate to each other in terms of degrees of angle. To me, every part of a knife relates directly to every other part of the knife. When I think over which grind would be best suited for a knife I take all parts of the knife into consideration, spine thickness, blade height, primary bevel angle, the length of the blade and most of all its intended use.
I figure most makers do this, whether they are conscience of it or not.

When it comes to referencing the edge grind it is, for me, a natural progression to tie it to all other parts of the blade. Since the cutting edge sits atop a blades two bevels I find the bevels themselves the best point of reference. Of course the bevel angle is directly related to the center line of the blade; So in the end, all the parts are related to all the others.

With the technique I use, I know the bevel angle for every blade I grind, with simple math I can relate it to any other part of the knife. The center-line or the bevels.

Thanks for posting your comments, Fred

 

[AVigil]

Fred,

Love my bubble Jig BTW

I watch your videos and I have a question. In your sharpening video you are putting on a 12* angle on edge while using the belt grinder. The BJ is on the ricasso, but when you take the knife to the diamond stone you put the blade on the 12* wedge and not the ricasso.

Is there a specific reason for using the ricasso on the grinder and then switching to the blade flat on the stone?

 

[colubrid]

I always think of knives in terms of degrees of angle. The pitch of the tang, the line of the spine and the grind of the bevels relate to each other in terms of degrees of angle. To me, every part of a knife relates directly to every other part of the knife. When I think over which grind would be best suited for a knife I take all parts of the knife into consideration, spine thickness, blade height, primary bevel angle, the length of the blade and most of all its intended use.
I figure most makers do this, whether they are conscience of it or not.

When it comes to referencing the edge grind it is, for me, a natural progression to tie it to all other parts of the blade. Since the cutting edge sits atop a blades two bevels I find the bevels themselves the best point of reference. Of course the bevel angle is directly related to the center line of the blade; So in the end, all the parts are related to all the others.

fred,

I want to send this off for a convex blade or maybe a whole reprofiling. What do you think is best for the blade type and thickness to have done to it?

 

[Fred.Rowe]

Fred,

Love my bubble Jig BTW

I watch your videos and I have a question. In your sharpening video you are putting on a 12* angle on edge while using the belt grinder. The BJ is on the ricasso, but when you take the knife to the diamond stone you put the blade on the 12* wedge and not the ricasso.

Is there a specific reason for using the ricasso on the grinder and then switching to the blade flat on the stone?

It makes no difference where the BJ is set when sharpening, as long you do the same on the reverse side of the blade. The reference is the bevel surface where the wedge sits.
Enjoy the BJ, Fred

fred,

I want to send this off for a convex blade or maybe a whole reprofiling. What do you think is best for the blade type and thickness to have done to it?

Altering a blade with this style grind, is limited by the grind itself. What don't you like about the knife?

What is your interest in a convex ground blade?

It looks like the edge needs reground; was the blade ground with a micro bevel, at the factory or is it a full chisel grind?

Fred