Lets Talk t.b.e (thickness behind the edge)

Here's how I see it . . . :D OR full flat with convex edge :)

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I don't mean to butt in, and maybe I'm thinking about it wrong, but I thought Deadboxhero's comment made sense...?

What I'm imagining is, say the bevels are ground down to 5 thousandths and the very bottom of the edge, thus leaving a slight flat area where the apex is supposed to be. After that you then grind in the apex, which will raise the shoulder up the sides of the bevels due to the grinding away of material on each side of the blade, thus making it thicker at the shoulders where the apex bevels begin, since they're no longer at the very bottom of the blade/edge profile.

Not sure if the way I worded that makes sense, but I'm willing to learn if I'm wrong in my thinking! :thumbsup:

~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)[
 
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There are several things in his comment.
1) You can't measure TBE before you sharpen the edge ….. it doesn't exist yet.
2) The change in TBE will depend on the edge angle.

Part of this issue is it is hard to accurately measure TBE. Everyone will place their micrometer at a slightly different spot. Most everyone uses a hand held device. Without at least 10-20X magnification and stationary measuring equipment, it is very inaccurate.

This is why calculating the TBE is the only practical method. Use the edge angle and measure the width of the secondary bevel.
 
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coldsteelburns said:
I don't mean to butt in, and maybe I'm thinking about it wrong, but I thought Deadboxhero's comment made sense...?

What I'm imagining is, say the bevels are ground down to 5 thousandths and the very bottom of the edge, thus leaving a slight flat area where the apex is supposed to be. After that you then grind in the apex, which will raise the shoulder up the sides of the bevels due to the grinding away of material on each side of the blade, thus making it thicker at the shoulders where the apex bevels begin, since they're no longer at the very bottom of the blade/edge profile.

Not sure if the way I worded that makes sense, but I'm willing to learn if I'm wrong in my thinking! :thumbsup:

~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)[
Click to expand...
That also makes sense to me. Stuart will have to enlighten us on why it doesn’t.
 
Calc Behind Edge Thickness (b.e.t), given Apex Inclusive Angle and Hypotenuse(length of sharpening bevel face). e.g. 15° and 1 mm:

b.e.t (Opposite) = 2*hyp*SIN(radians(angle/2)) = 2*SIN(angle*pi/360) = 2 *sin(0.131) = 0.261 mm (0.010")


Calc Apex Inclusive Angle(a.i.a), given Opposite and Hypotenuse. e.g. 1 mm and 2 mm:

a.i.a(acute) = 360/PI() * ASIN((opp/2)/hyp) = 114.59 * asin(0.25) = 28.96°
or
a.i.a = 360/PI() * ATAN((opp/2)/sqrt((hyp^2-(opp/2)^2)) = 28.96°
 
There are lots of triangle calculators online for those that are uncomfortable with the math.
 
You are correct. I had my calculator set on one significant decimal place. My point was that the only practical way to get an accurate measurement was calculating it.
 
razor-edge-knives said:
Convex vs flat? Where's my popcorn?! :D
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:)
It is pointless to discuss about this , don t you think ? samuraistuart samuraistuart nailed it .........
IMHO, Knives should be as thin as possible but still able to do what the knife is intended for. Thin spines. Thin grinds (low BTE thickness), and low edge angles. Get the heat treat nailed.
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able to do what the knife is intended to do ........end of story .
 
I am going (at some risk i think :-) ) to pull this thread back up to ask a follow up question. Everyone says”thinner is better” - yeah, i agree. Recently in thinning my blades (-wider cooking knives, not field knives) i have no problem getting down to, say 0.008” with FFG. Is more work to get down thinner, but just takes more time, and that is fine.

stacy says you take a edge down to basically zero when grinding the primary bevel. Two things: when getting down below about 4 mils, on one recent blade i just started seeing a ragged edge (carbide pullout? This was AEBL and 120 grit). The other is, when getting down to those thicknesses it is insanely easy to overheat the edge.

so ... how the heck do you grind a primary bevel thinner than about 5 mils or so? Shift to 220 grit (more heating!) and use a water cooling system???
 
..slack belt gator...you can mess with tension to get the desired amount of convexing. The edge stays cool for me since there is no platen / far less friction/heat build up. Material removal is very slow and at this point that is a good thing. Hand sanding takes care of the very last little bit. After that I use a water stone to apply the primary bevel by hand. Basically Im removing any ragged wire edge and refining the primary bevel until a good strong/sharp edge is formed.
 
timos- said:
..slack belt gator...you can mess with tension to get the desired amount of convexing. The edge stays cool for me since there is no platen
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Hmmm. What grit Gator? right now I am going from a 120 ceramic then to a A100 (220 grit) Gator ... but am using the gator more for surface finish refinement, and trying to take the edge for the primary bevel down to 1-2-3 mils using the 120 ceramic (confusion: I am calling the "main" very wide bevel the "primary" per recommendation of Stacy).

Sounds like you are using the A100 Gator to bring that edge for the primary bevel to that 1-2-3 mil thickness???
 
120 grit ceramic is also the last ceramic I use. Usually norton blaze. Then I actually use a A300 gator for the last bit of real material removal and then the A160 and so on for refinement. However, I go back to the flat platen for refinement. This leaves the gently convexed edge unscathed as you refine grits on the grinder. When I hand sand I start with 220 or 280 grit, it takes a good hour with a hard backer to get up to the next grit size. I use a rubber backed sanding block for the convexed areas of blade. And from there it is smooth sailing. That process allows for a bevel that is actually pretty close to being flat ground for ease of finishing but with convexed edge for performance. I personally also allow the spine of my knife to get washed out a bit, this happens during that A300 slack belt convexing of the edge. I dont like the look so I add in a shallow false edge to the spine, which i think also looks cool.

Another important "discovery" for me was learning how to grind in distal taper vertically on the platen. I believe I read that Stacy does it this way. Well lo and behold this was probably the light bulb moment for me in terms of achieving that kind of performance where the user can pass the tip through an onion with almost no resistance.
 
timos- said:
hen I actually use a A300 gator for the last bit of real material removal
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thanks. I need to order some steel from Pops, might pick up some 300 and 160 gators to try. I know there is some, ahhh, "discussion" re. flat grind versus convex grind at the tip - I will stay away from that discussion, but will try this.....

timos- said:
Another important "discovery" for me was learning how to grind in distal taper vertically on the platen
Click to expand...
I have not tried this yet. Any hints on how to do this: Do you use a contact wheel instead of a platen?
 
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