A DIMES THICKNESS....My Two Cents Worth

Stacy E. Apelt - Bladesmith

Stacy E. Apelt - Bladesmith

ilmarinen - MODERATOR
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Knifemaker / Craftsman / Service Provider
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I have seen so much lately about edge thickness that I thought a post with some thoughts on edge thickness would be appropriate.

First, I plead guilty in using the term "About the thickness of a dime" in giving newbie blade making instructions.
The tendency of most new makers to file/sand the blade right to a sharp edge before HT is so much a problem, that I try to slow them down a bit. Most shoot for that thickness, and end up about half as thick .

A dime is around 1.2mm, or .045" thick. It is an easy item to use as a comparison when micrometers aren't around. In the days of my youth, dimes were silver, and wore down to about .030" or less before they were unrecognizable. Thus the term, "Worn thin as a dime", or "One thin Dime".

However, the thickness of the edge of a blade before HT should normally be a bit thinner than a dime.
.030" or just shy of 1mm is a good target for most carbon steel blades, and .015-.020" or .5mm is a good range for a stainless blade.

After HT you have to sand/grind the bevels until the edge is almost sharp...about .005", or .1mm.....will give you the standard edge thickness when you start the final edge. A fillet blade may go to .002" or .05mm before sharpening.

The reason many knives that seem sharp won't cut worth a dang is that the edge may be sharp, but the blade is an axe as far as thickness near the edge goes.

The edge thickness needs to match the steel type, blade size, and style. A honkin' 1/4" thick Bowie or camp chopper in 1095 will need a lot more edge at HT than a .060" thick S35VN fillet blade.

The question of when to sharpen is easily answered by this simple reply - "When there is nothing else to remove from the blade, and nothing else to do on the knife."
 
Amen, Stacy.

Thanks for posting this. I found out the hard way a while back that the dime thickness thing was a little misleading (on the fat side). At the time, I didn't know there was a difference for stainless, either. My first grinds had fat edges. I didn't know how fat until I got a micrometer because they all looked thinner than a dime!

Some new makers will really benefit from this post, I know I would have a while back.

Erik
 
Yup, had issues getting truly sharp knives until I started going thinner. I aim for dime knowing that final adjustments before HT will take it slightly under, then post HT cleanup will get me right about where I want. My more recent knives are much better cutters than earlier work.
I'm finally back in the shop a bit too, have one tempering right now that I am going to use my first natural wood handle on.

Anyway, yet another +1 and thank you, for Stacy and the helpful advice for us noobs. :)
 
Thanks for the lesson Stacy....will save money on belts by taking them thinner before H/T.
 
Why the difference between the recommended edge thickness for carbon and stainless? Is it a matter of relative dimensional stability or between oil/water hardened versus air hardened HT?
 
zerogee said:
Why the difference between the recommended edge thickness for carbon and stainless? Is it a matter of relative dimensional stability or between oil/water hardened versus air hardened HT?
Click to expand...

Stainless steels and higly alloyed steels usually require very high austenizing temps and long soak times to harden, and have to be protected from oxygen during this process or they will incur very heavy decarb and scaling, to the point of ruin. So they must be protected from oxy during heat treating, which means that they genrally come out with no decarb or scale, and therefore they can be ground to very near the final dimensions before heat treat.
Carbon steels and simpler alloys are usually austenized at much lower temps, for shorter hold times, and are often done without protection from oxygen, so they come out with at least a modest amount of decarb and scale, which is usually ground off after heat treat. The extra edge thickness that is usually left on carbon steels before HT is to account for this.
 
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That, plus an oil quench has a much higher chance to warp the blade and edge than stainless, which air cool and usually are clamped between aluminum plates.
 
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