Recommendation? Why can't I get the sharpness I want?

K

Ky_Dylan

Joined
Jan 26, 2020
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I am a looking for advice, answers or recommendations.
I have forged a knife from an old farrier rasp and I'm having trouble getting the edge I want. Its some what shrpe ,on a 1-10 scale it's a 4 maybe 5.
I dont understand because the last rasp knife I made using rasp, same heat treat/temper grind etc. came out sharp enough to split hairs
 
It could be that this rasp was a different steel or was only case hardened... or something in your forging wasn't exactly the same.

Did you normalize it after forging?

Maybe you rolled the edge? Can you feel a burr still hanging on?

Lots of factors here :)
 
Geometry and heat treat are the two biggest issues. How thick is the edge before you started sharpening it, and secondly, how did you heat treat the knife? What is the hardness? (Will it skate a file?)
 
allenkey said:
It could be that this rasp was a different steel or was only case hardened... or something in your forging wasn't exactly the same.

Did you normalize it after forging?

Maybe you rolled the edge? Can you feel a burr still hanging on?

Lots of factors here :)
Click to expand...
Yes sir I normalized. The spine was thicker and the whole blade had noticeably more mass. After I normalized I brought it up to a bright orange and quinched it in canola oil and it didnt pass the file test so I did a repeat
 
This has a bit more mass the the first one..any good tips for the heat treat? I'm handy with a hammer but I'm as green as it gets..my heat treat process is the same every time..i run the normalizing cycle 3 to 5 times.. I heat it up until demagnatized and let it cool to touch and on my heat treat I bring it up to a bright orange and quinch. In canola oil/ temper at 400 degrees for 2 hours
 
I guess I will be the one to rase my hand and say sharpness is not inherently a function of hardness. Hardness allows sharpness to be wear resistant and not deform under load. But if your having an issue getting something sharp I would not blame the heat treat. I would wager a bet that proper technique could produce a hair splitting edge faster and easier on soft(er) steel then steel that’s much harder. If anything I have seen hardness affect sharpness negativity when pushing hardness to the max. Soft steel is really easy to strop and creates a very fine wire burr on the edge. Hard steel is more likely to micro chip and create an edge that’s not as fine as what you could produce on something that’s softer. It is entirely possible to sharpen mild steel to be saving sharp. It won’t hold that sharpness long because it will be easy to deform but it will be scary sharp.
 
When the steel is harder with good HT, the burr breaks off easier and is less stubborn. The apex forms better, Less wire edge. Can hold a crisper edge longer too.
Any difficulty sharpening harder steel is from poor quality abrasives and technique.

Sharpening technique is king, review your process and see if you can improve.

I'd also recommend dumping the rasp steel and getting some 26C3 "Spicy White".
 
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