School me on some sharpness stuff..

It is a tough thing to figure out (how much to grind) but try to grind most of your edge thickness tolerances with a fresh 80 or so grit ceramic belt, this helps a lot with heat. After that use gator (3M 337DC) belts to finish but not to remove a lot of metal, that is when things get hot... also more hot with higher grits, high speeds or worn belts.
 
Blackdirt cowboy said:
I’m just scared to go any thinner. I’m pretty new to knife making and I’m afraid I’ll ruin the temper on the edge.
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Do you have a variable speed grinder? If you do try grinding down to around .01 or less with a 120 grit ceramic belt. With lower speed that should be easy enough to do. After that I slow down the belt and use a spray bottle with soapy water every few passes. Also add a little soap to your dunk bucket. This helps the water to sheet the surface better. I like to do my final grinds lengthwise on the platten. The water will run down to the tip and keep it cool as you clean up the grind lines. .007 to .002 or so is a great place to aim for on kitchen knives.
 
Yes I have a variable speed grinder. I’ll try that with the soapy water. The last knife I ground was a hollow grind I took to .03” and I burned all my finger tips trying to get it that far. Perhaps I should slow the belt down even more. I think I was running at 50% speed on that one.
 
I don't understand the thicknesses people are giving??
Hair shaving sharp is thin sharp. The edge should be below .01" before starting to sharpen it. I take it to near zero ( almost sharp) before sharpening. I doubt the edge is more than .003-.005 when I start to sharpen.
A .03" thickness is 1/32". There are knives made from sheet stock that thick.
 
Stacy E. Apelt - Bladesmith said:
I don't understand the thicknesses people are giving??
Hair shaving sharp is thin sharp. The edge should be below .01" before starting to sharpen it. I take it to near zero ( almost sharp) before sharpening. I doubt the edge is more than .003-.005 when I start to sharpen.
A .03" thickness is 1/32". There are knives made from sheet stock that thick.
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I hope I didn't give the impression that I was recommending edges that thick. I simply meant that for cutting hair on your arm thickness isn't as big of deal since it is the apex that catches the hair to cut it off. When cutting thicker things it isn't going to cut well even if the apex is sharp. I can sharpen a axe to shave with but I don't want to cut up dinner with anything that thick. I find that somewhere around a .003 to .005 edge thickness is not that hard to achieve. If someone is worried about over heating the edge they can thin it down into that range when hand sanding. Stacy has given good advice about how to make a high performance blade as well as how to get a good edge.
 
Blackdirt cowboy said:
Yes I have a variable speed grinder. I’ll try that with the soapy water. The last knife I ground was a hollow grind I took to .03” and I burned all my finger tips trying to get it that far. Perhaps I should slow the belt down even more. I think I was running at 50% speed on that one.
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Pressure is the key here. Let the machine do the work. Light pressure and take your time. I was burning my fingers on every pass until I reread some grinding advice threads and light pressure is really important.
 
When I get my edge below .01 I am definitely using a 120 grit belt and going slow (maybe 50 or so on the vfd). Spray water on the belt, and dunk every pass. Never keep the blade stationary... and my fingers are on the blade feeling for heat. If it gets too warm or hot, I am overdoing it and immediately dunk. It is a slow but steady process to work that edge down - for a 6 inch or longer kitchen knife it takes me maybe 2 hours to get down to around .004 - .002 (I don’t go thinner because I don’t convex). I had a thread about this time question a while ago, and some said it should not take that long ... but without going to a coarser grit (which I don’t want to at that point), this is hat it currently takes me...
 
I make my Mini-dashi model in .049" stock! The edge is probably .003" before sharpening. There is really no need to ever go over .015" and to me that is pretty thick. A thick edge can be great for a piercing blade though.

On the variable speed turn it down to maybe 10% once you get thin. As grit goes up speed goes down and vice versa.
 
Ive started watching the water on my blade as I grind. I can see it starting to move back from the edge and disappear and I know it is going to get hot quick. Grind without gloves and you feel it coming and then I either lighten up my pressure or get it off the belt. I've been grinding yesterday and today and haven only had one "ow!" moment, but lots of feeling the heat coming moments. Speed pressure and water matter.
 
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