Blade grind/edge geometry, sharpening

Scott,
Good info right there, thanks bud.
I thought i might see that Albino Tusker on here as a demo or in the background somewhere...;)
 
Thanks guys. I hope it was easy to understand. As far as the measurements behind the edge that I talked about, you can go thinner but I've found that the specs I use seem to work fine. I have gone as thin as .040 & .035 without any problems. The final cutting edge is really what matters the most in a knife's ability to cut well. Steel type doesn't matter as much as geometry and heat treat/temper. If it's a quality cutlery grade steel, it will work as long as those two things are right.
Scott
 
Scott,

This was very timely. Thanks again for another very informative video. I have learned a great deal.
 
Great video Scott. So, just to clarify, the measurement you are taking is about 3/16 to 1/4" behind the edge? I've been going around and measuring all my knives and I don't have one convex ground blade that is that thin except one that was ground from 3/32" stock. I just want to make sure I'm measuring from the right spot.

What are your thoughts on convex vs. flat for outdoor/woods/bushcraft knives? Does the same geometry apply in your experience?
 
Jared, the measurement is on the primary grind above/behind the cutting edge. I've measured alot of different knives. Hollow grind knives run thinner behind the edge, some as thin as .025, mostly on folders. I've measured some on the different popular outdoor production knives that were as thick as .090 behind the edge! That's thicker then some of my full size axes!
I've found going full convex to be too steep/thick behind the edge that's why I changed to 80% flat, 20% convex. The convex part of the grind is flatter when done on the rotary platen then it is if done on a slack belt, making it have better geometry. Flat grinds are great for small to medium knives but I prefer that convex contour on larger knives because convex will push material apart better when chopping and splitting. Flat grinds done right with thin geometry behind the edge tend to stick in the material. Flat grinds left thick behind the edge with a thick secondary bevel will split better but are hard to sharpen and keep sharp.
So either convex or flat will do well for bushcraft knives if the grind/edge has good geometry. I think some makers/companies go with thicker edges because of the possiblity of edge failure. There are alot of knuckleheads on youtube doing stupid things with knives. If everything is done right, geometry/heat treat/ temper, then the blade will perform properly. Anybody can break anything if they try hard enough.
Scott
 
Scott, thanks for that info. I was measuring a little back from the edge itself and getting a much thicker measurement. You have me intrigued by the 80% flat 20% convex idea. Is the grind flat behind the edge and then turns into a convex as you go up on the grind? Or is it that the convex is just much flatter due to using the rotary platen?

Great info that you are sharing here. Finally having someone explain geometry in a video is invaluable. It also shows that a good knife maker not only has a steady hand but has spent the time testing and perfecting his knives.
 
Jared sounds like you were measuring back from the edge as I explained. It is behind the edge heading toward the spine about 3/16" to 1/4".
My grinds still have a convex contour added to the flat grind. I leave enough steel after flat grinding to be able to convex 20%. The rotary platen has the rubber belt backing the abrasive belt which adds more resistance then the slack belt attachment which has no backing behind the abrasive belt which can cause a more abtuse convex contour. Thus using the rotary platen gives a flatter convex contour giving better geometry.
Scott
 
That makes perfect sense. It must be why your knives work so well. Sounds like you have perfected controlling the convex geometry rather than letting the slack belt decide it for you. Yet another reason why I have almost completely shied away from buying production knives.
 
Jared, as I mentioned in the vids, production and some makers add the secondary bevel when there is still too much steel thickness right at the edge. Even adding a convex edge to a flat grind that isn't thinned down enough will not cut very well. No matter how you try and sharpen the knife, you will get nowhere getting it sharp. What you end up having to do is reprofile by thinning the edge by hand. Loooong process by hand. I've reprofiled/thinned down so many knives over the years, I've lost count. One that comes to mind is the TOPS Tracker. I've done many of them.
Scott
 
As a new guy to knifemaking I appreciate the videos you post here as well as youtube. The information has helped me a great deal as I learn the art of knifemaking. Please continue to teach as I strive to learn.
 
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