We started to have a discussion about sharpening HAP40 in the Recommendation Q&A section. I didn't want to high jack that thread too much so continuing the discussion here(quotes are from previous thread)
Tall Dark and Swarfy wrote:Shapton Pros work just fine. If you're going to to crazy with high grits you will want to use diamond above ~5K so as to be able to shape the Vanadium and Cobalt carbides and not just abrade away the matrix.
mark wrote:I don't have any Shaptons above the 5k, but I'm curious... Why would the Shapton pro or glass 8k be ineffective?
Tall Dark and Swarfy wrote:This should stir lively debate. The Shapton abrasive is less hard than the V and Co carbides. Thinking of the steel as chocolate chip cookie dough, the Shaptons will eat the dough but leave the chips which will eventually fall out. Using diamond when you're in the high grit range actually helps shape the carbides. At least that's the theory.
So you are saying the Shapton stones will work fine below 5k, but above 5k their magic stops working? Wish they would put more magic in their higher grit stones
I understand the chocolate chip cookie dough theory. I was more or less looking for clarification on why exactly 5k was the predetermined stopping point for stones. I'm going to layout my understanding of the cookie dough theory(for those reading along) and my hunch as to why 5k is the stopping point.
Hard carbides like tungsten, vanadium and colbalt (chocolate chips present in HAP40) are unable to be cut by the abrasive in the stone as they are too hard. The largest of these carbides are between 2-3 micron in size. Stones that have larger abrasive particles than vanadium, for instance, are able to sharpen the steel as the stone abrasive can reach the softer material(cookie dough) between the vanadium carbide which holds it into the steel matrix. By removing softer material(carbon, chromium and Molybdenum in HAP40) holding the carbide it will effectively fall out.
Stones such as the Shapton 10k, with 1.5 micron abrasive, do nothing to refine the edge as they can not cut vanadium carbides. Thus they can not refine the edge past the 2-3 micron size of the vanadium carbides. In relation to the cookie dough, you can remove as much dough as you want, but there will still be the large chips exposed at the edge.
Feel free to correct any mistakes. Am I correct in my hunch that the carbides unable to be cut are 2-3 micron in size? Always the same size regardless of steel makeup and heat treat?