Azula Gun Holsters
Knifemaker / Craftsman / Service Provider
- Joined
- Sep 19, 2016
- Messages
- 1,097
Oh yeah, those paper wheels can be terrible. I'm not saying it isn't possible to get good results with something like that, but anything that is spinning screaming fast is going to burn your edge a little.
Rather than duplicate my thoughts this was my response to a burned edge argument over on USN a while back:
It wouldn't surprise me if many (most?) custom makers who sharpen a lot of knives dry occasionally have areas of at least slightly burned edges and don't know it.
It's simple. If you take two identical knives in an alloy like S30V and grind one edge dry (be a little bit sloppy with your pressure, feed rate and belt sharpness, you're looking for a worst case but potentially plausible version of your normal process) and grind the other edge in slow and wet, then sit down with both and whittle some wood for a little while then look at the edge under light and magnification. When I did this the difference was very clear and unambiguous. Obviously the angle has to be closely controlled, not just eyeballed, for a meaningful comparison and a reasonable angle (obtuse edges don't burn as badly). If a maker hasn't done this simple thing their opinion on the subject really isn't very informed. I've done it and I changed my process because of it and I'll bet I sharpen more knives in a year than most folks here.
I just did a little bit of math looking at a theoretical blade of these dimensions:
FFG, .150" at spine, 4 DPS primary grind angle, 15/16th blade height, .025 BTE, sharpened 18 DPS
The sectional area is .0786877
The sectional area of the edge .005 back from the edge is only .000008123.
That gives a mass ratio of the blade to .005 of the edge of 9687:1. That's a lot of orders of magnitude difference. If you were to instantaneously raise that .005 of edge area by 1000F then let it equalize into the blade it would raise the temperature of the entire section by only 1/10th of a degree.
In practice it isn't instantaneous but this illustrates why making judgments about the temperature of some very small area that is some distance away from your finger tips based on the temperature your fingers feel isn't very accurate.
I'm not trying to be argumentative or snarky here. Some people manufacture knives that are expected to have very good edge retention out of the box and others may make knives where it really isn't that big of a deal so long it's just a few thou near the edge that is affected and it still works reasonably well. There are all kinds, and that's great. But I wouldn't dismiss something that is so easily verified just because your own experience hasn't shown it to you.
All of that said, S30V is not rocket science to sharpen on powered equipment and get it truly sharp with a quality edge. It is simply not a big deal. Unless you're burning the edge trying to sharpen it. Which people do. Then you can get this exact situation.
Good to know. Will have to look at the issue of heat closely.
Possibly a dunk in water after each pass ?
