Edge thickness behind the cutting edge help?

E

ev13wt

Joined
May 28, 2014
Messages
536
Gentlemen,

I am working on my 4th knife and no I won't show you the others, too embarrassing :) . (Well ok my 3rd maybe: http://www.pirate4x4.com/forum/general-chit-chat/1098563-ev13wt-build-his-3rd-knife.html ) :) Since I am a pretty "planning" sort of person and like repeatability, I tend to theorize the crap out of things before I fire up the grinder.

This blade is pre-HT, and rough ground. 3mm spine (0.118") tapering down to 2.5mm (0.098") at the tip currently. When it gets back from heat treat I need to finish its grind lines and down to where I will put a secondary 30° incl. bevel on it.

Here is my brain fart: What edge thickness am I shooting for at the top of the 30° secondary?
I understand the thicker it is here, the taller my 30° bevel will get, but is there a baseline I should be shooting for? The thicker the stronger it will be but 1mm (0.039") edge thickness here will give me a 2mm tall secondary bevel, 0.5 (0.019") will give a 1mm tall bevel which "sounds" about right. Or is this all still way to thick? Or does it not matter much because 30° is 30°. I don't wan't it to be a wedge obviously. Or is this just something I need to try and test?

Where I can I read up about this or does anyone have a tip for me? I tried searching of course but got nothing really except some kitchen knife measurements.

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What are you going to cut with it? That will change the answer.
 
You are over thinking this. I grind all mine damn near sharp before hand sanding and the secondary bevel is tiny when sharpened. Thinner edge cuts better!
 
I like Don's answer. I used to "overthink" edge thickness as well. .005" to .010" are good numbers. Just grind it down to where it is almost an edge, and then sharpen. The style of your knife is not a chopper, but a slicer, and as such you want a thin edge on it.
 
I like Don's answer, too. I got about 2/3 of the way through your post and was totally lost. Waaaay overthinking it.
 
Most of what I've learned has been on my own through trial and error. Edge thickness before sharpening being one of those lessons. My first few knives were about .015"-.020" edge thickness before sharpening. I quickly realized that was way too thick. I got better and now aim for .005"-.007". The closer to .005", the better. If the heat treatment for your given steel is optimal (I use Peter's and I trust that it is), you shouldn't have issues thinning it down that far. It makes for a much better cutting tool when the bevel and edge geometry are right and IMO, being right, equals being very thin.
 
Just take the primary bevel to near zero (just getting sharp) and then add the secondary at the desired angle. The thickness at the top of the secondary will be whatever it should be. If the edge does not hold up in heavy use, just sharpen the secondary back a little more....... no math no thinking about it.
 
I think too much :) Thanks everyone for the tips. When it comes back from HT I will take down to really thin and then give it the secondary bevel. The tip about if it is too thin and chips or folds I will increase the secondary until it works is great.

Thanks! I'll report back when I'm done with it!
 
Don Hanson III said:
You are over thinking this. I grind all mine damn near sharp before hand sanding and the secondary bevel is tiny when sharpened. Thinner edge cuts better!
Click to expand...

ev13wt said:
When it comes back from HT I will take down to really thin and then give it the secondary bevel. The tip about if it is too thin and chips or folds I will increase the secondary until it works is great.
Click to expand...

I concur :)

Don't feel too bad about over-thinking/being obsessive about things. That sort of comes with the territory. But usually we find that keeping it simple is best.
 
Thanks :) I hate it when this happens :/

Many here inspire me with their work and helpfulness to learn and each lesson learnt is time well spent. "Doing something "on the quick" usually comes back to bite me twice" was a good lesson. Thus this thread. Seems it goes both ways I have found myself looking at a piece of steel for an hour or two as well, deciding on a fourth inch of cut..... Then I either go home and do something else or starting working without thinking.

Sometimes it turns out great and sometimes it end up in a growing scrap pile. Then in the morning, after seeing what some of you guys build I go to the shop and "great" ends up in the scap pile too. :thumbup:

Regards, Ben
 
Yeah....

Do what Don said.

Works every time
 
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