What angle do you measure?

[cbwx34]

If you have a blade that is ground 5° per side (see picture), and you sharpen it at an angle measured 20° from horizontal, do you consider the edge sharpened at 15° or 20° ? (Setting aside the 'actual angle doesn't matter' argument.)

 

[jc57]

Depends on how you measured the angle.

If you used a 15 deg. angle guide that the flat of the blade lies on, then your angle from the true midpoint (the apex) is 20 degrees, so the edge itself is 40 degrees inclusive.

If you use something like a Sharpmaker, using the 30 degree slots and held the knife vertical during sharpening, the angle is 15 degrees per side, or 30 degrees inclusive (assuming the Sharpmaker is perfectly true to the slot markings).

 

[REK Knives]

Not sure I understand what you are saying... Do you mean measuring the angle from the center line (like on a weps) or are you meaning measuring off of the flat grind (like with an edge pro)

 

[wiredbeans]

If you sharpen horizontal at 20 then it will still be 20.

If you use the main bevel (the 5 degree) as the horizontal line then it would be 25 degrees if your sharpener is contacting the knife from top down and on the left side as pictured.

If the sharpener is contacting the blade from bottom up (belts or grinder) then It will end up with 15 degrees if the knife is positioned as picture with the edge tilted up to make the main bevel horizontal.


Sent from my iPhone using Tapatalk

 

[cbwx34]

The W.E. and Sharpmaker are good examples... the knife is held vertical and the angle is measured from vertical. But the actual angle between the edge and the knife's grind would make the actual angle different. If I sharpened the pictured knife on the 30° setting on the Sharpmaker (15 per side) the actual angle between the edge and the knife grind would be 10°... vs. another knife, say a kitchen knife that's only a couple of degrees.

The Edge Pro is another good example... set the EP at 20°... if I lay the knife on the 5° blade grind, I'm sharpening at 15°. (In fact, I think one of the EP videos shows directions on compensating for this).

Just wondered if there's a consensus... I'm getting the impression it's not accounting for the angle of the blade grind? So, to eliminate how it was sharpened... if I handed you the pictured knife, and asked you to measure the angle it was sharpened at... would you measure from an imaginary centerline that ran straight thru the blade... and disregard the blade grind angle? (Might have been the easiest way to ask this).

 

[bucketstove]

...if I handed you the pictured knife, and asked you to measure the angle it was sharpened at... would you measure from an imaginary centerline that ran straight thru the blade... and disregard the blade grind angle? (Might have been the easiest way to ask this).

Hi,
yes, when people talk about edge angles, its the angle from imaginary center line ...
it doesn't describe the whole knife,
its only one measurement ( half the edge description , other half is thickness),
but is a general indicator of what a knife should be able to handle
For some examples see optimum knife edge angles and what they should be able to do/slice/chop

Hi

Yes, it depends basically what the other guys said

Consider that under 15 dps edge can chop bones
And 12 dps edge can still shaves/whittles beard hair after 1000 slices of hardwood

So if you're chopping rocks and bricks, 25dps might resist damage better than 20dps,
but if you're slicing stuff, 25dps dulls faster than 20dps even if those are microbevel angles

So, recommendations for 25-30 degrees per side sharpening angle
are great for first time sharpeners or if you only have seconds and need results quick,
much better than a dull knife
... but try and do a couple hundred slices with that edge angle ... ouch

 

[Jason B.]

The blade grind is not a factor when measuring edge angle. Edge angle is always measured from the center line of the knife.

How the knife is ground and its angles make up blade geometry, which is a distinct and secondary factor in cutting performance. Truthfully, blade geometry is the primary factor in blade performance while the edge is secondary.

 

[cbwx34]

Cool... thanks. It's what I thought... then I was watching a video where it was being measured off the blade's grind, and it kinda threw me since I hadn't seen that before. (And totally agree about the geometry).

 

[bgentry]

I just wanted to say that this same set of ideas led to me being confused about angles with respect to knife sharpening a while back. I asked a fairly similar question here and got good answers about the center line being the only true reference for blade edge angle.

Understanding the geometry of the blade, from the primary grind to the edge grinds, is part of gaining a better understanding of blades overall. Which is a great thing!

Brian.

 

[Fred.Rowe]

When a knife maker designs a knife it is done from the center line of the proposed blade. Each angle, whether its distal taper, primary bevel, or sharpening angle, they all are relative to the center line of the blade.
Doing this really helps when discussing a blade you want made by a knife maker living half way around the world. If your not both working from the same datum you could end up with a very strange looking knife


Fred