Question on flat ground edge thickness...can you help me?

G

godogs57

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Apr 16, 2004
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Up till now, every knife I have ground has been hollow ground, excepting three...this one is my third one. I have finished heat treat and tempering and an now finish grinding, hand polishing my 5160 forged blade.

My question is how thick do you leave it prior to sharpening? Do you grind to "infinity" or leave a little bit? Right now my blade has about a hair's thickness on the edge...should I leave it there or take it on down to nothing?

Thanks for any advice!
 
the type of grind really doesn't matter... But first a few questions... is it heat treated already? if it is yes take it on down. if it isnt, we need to know what kind of steel your working with. ( i.e. A2, O1, W1, 5160, 154cm, S30v, etc.) when we know that and if it's heat treated or not we can help you. :D

Jason
 
I know my blades are much smaller on average (slipjoints) and I grind all my blades flat.For the most part I do all my grinding after heat treat except on certain blades.I regularly grind to under .010 before sharpening.

Ken
 
Like I stated above...its 5160 steel and yep, its heat treated and tempered. I'll leave a bit on there per y'all's instructions and see what happens. Thanks!
 
OK not to hijack this thread, but why does the type of grind matter? I'm confused. Be it hollow, flat, or convex, pre-heat treat edge thickness, to me, should be the same for X steel.

Jason
 
Jason, I have seen, in a number of comments, folks who flat grind their blades grind right on down to the edge and all they have to do is whip it a couple of strokes on the crock sticks and there is your finished edge. My hollow ground blades are not ground in that manner, leaving an edge about .020 before sharpening. I was wondering what the majority do, since I didn't know, with respect to flat ground blades.

Edge geometry of flat ground versus hollow ground blades would indeed dictate a different thickness as a starting point I would think. I just didn't know.
 
Depends on the type of knife, success of the HT, the hardness, the edge type...

If it is a kitchen knife or a skinner (only cutting action) I always leave very thin (something like 0.01 - 0.005) edge then put an edge on it.

It it is a chopper, a big knife, I leave thicker edge (like 0.04 - 0.02) and put a convex edge.

There are lots of different types of knives require different types of edges with different thicknesses. The most efficient way to determine the thickness is to test the knife. If edge is too thin or too thick you'll notice while testing the knife to its limits...

Emre
 
Ok so we're talking post heat treat then... I thought we were talkin PRE heat treat! but then again, the steel choice could make all the difference in the world!
What you guys said makes sense. The pre heat treat edge is left thick (.040-.062" on some!) to avoid cracking during quench in some steels. But others, mostly air hardening, I believe, you can take it to almost final edge (.020" or less) without really a risk of cracking during quench. But I still dont understand why the type of grind dictates edge thickness? For instance I use a VERY shallow hollow grind (24" wheel" :D) so it's almost flat! And routinely grind to a .050-.060" edge when working W1/1095 and even 5160. Could I safely go less with the 5160? I've never tried.

Jason
 
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Jason, I feel a flat ground blade taken to a 0 edge on a utility knife is to thin not enough meat behind it. That's where the convex edge comes in. Emre nailed it with his post saying the edge grind has to fit the use of the knife.
 
Ok I think I understand more now. I can see how use can dictate the type of edge. thank you all for clearing that up :D

Jason
 
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