How do you properly measure "behind the edge"?

[Omega Leather Works]

Hey guys, I just bought a digital caliper. One of the reasons why I bought it is because I'd like to measure my blades behind the edge.

May sound silly, but now that I'm trying it I realized that I'm not exactly sure where the measurement is taken.

Some of my knives (okay, most) have a fairly tall bevel because I reprofile in order to make a more acute bevel. Is it just above the bevel, or literally just above the apex? If neither then where?

 

[BluntCut MetalWorks]

measure at the bevel shoulder. also take the bevel angle & face length into account - e.g scandi. a lazer would have low edge angle and short bevel face.

 

[bpeezer]

and if you don't know the bevel angle, you can calculate it using the thickness behind the edge and the face length and doing some trigonometry

 

[Omega Leather Works]

and if you don't know the bevel angle, you can calculate it using the thickness behind the edge and the face length and doing some trigonometry

Haha trig? Err no.

Thanks guys, I get the gist. My Contego sharpened at roughly 30° shows .020 which seems good. I'll have to figure out the rest.

My GEC regrind shows .010 it's a zero edge, I measured about 1/16" from the apex. That knife is a scalpel, although fairly frail.

 

[KennyB]

and if you don't know the bevel angle, you can calculate it using the thickness behind the edge and the face length and doing some trigonometry

I wouldn't rely that much on this though, because it's going to be impossible to get measurements more accurate than +/- .005" and variances that much will throw off the results too much for it to be that accurate.

 

[bpeezer]

I wouldn't rely that much on this though, because it's going to be impossible to get measurements more accurate than +/- .005" and variances that much will throw off the results too much for it to be that accurate.

Not if the bevel is super duper thick

 

[Chris "Anagarika"]

Not if the bevel is super duper thick

Or like Scandi, super wide ...

Edit to add, found this thread: www.spyderco.com/forums/showthread.php?53572-Thin-edge-low-angle-M390-Para-2-how-low-is-too-low that shows how thickness behind edge being measured.