How thin to grind?

[i4Marc]

For the more experienced makers here, how thin do you take your edge before hand sanding and sharpening? This may trigger inquiries for more details about the knife so here are the specs: Bowie, 8" edge, 1.75" wide, 80CrV2 steel, triple normalized, triple quenched, triple tempered at 400 degrees. This will be a working knife that will see some chopping.

 

[Stacy E. Apelt - Bladesmith]

Well, the edge thickness was already decided when you decided it was ready for the HT. That is what you will have to deal with in the hard steel now. Normally a big knife in 80VCrV would have an edge about .020-.030 at HT.

After HT you clean it up and make sure the surface is flat and smooth. This can be done on a grinder with constant cooling dips in water, or by hand. Once the blade is flat and smooth at 400 grit, the edge should be about .010". Then you hand sand to the final grit. This can be 400 or 8000, depending on the finish desire. The edge will get a bit thinner in this final sanding, but that doesn't really matter. However, if it gets sharp in hand sanding, just flatten it back a tad with some 220 grit paper run along the edge.
After the surface is hand sanded, polished, etc., the knife is finished by putting on the handle and any fittings. The blade is wrapped in tape to protect the finish during all these steps. Once all is complete, the final edge is put on at whatever angle fits the blade type. For a Bowie, I would suggest 20° per side.

Just for informative purpose, there should be no reason to triple quench 80CrV as it is eutectoid and has no excess carbon to deal with. Probably won't hurt, but shouldn't help either. If the "Triple Quench" was cycling the steel for fine grain, it won't hurt anything, but the Vanadium is in the alloy for that purpose. The temps should be about 1550°F for the first quench, about 1350°F for the second, and the target temp for the final one.

 

[i4Marc]

Hi Stacy,

Thanks for the reply. Just to clarify, I rough ground the bevels before HT to ~ .065 inch. I did all three quenches at 1500* with a 5 min soak. I'll keep your procedure in mind for my next blade. After HT I carefully ground nice flat bevels to where they are currently @ .015 inch. with a good dip in the water bucket after every pass or two. The edge thickness I was referring to in my OP was covered later in your answer. I am getting ready to hand sand but I didn't want to do all that sanding and find out afterwards that I should have taken the edge to your suggested .010". So that was the piece of information for which I was waiting. I will go back to the sander and take it down to .010 then begin the hand sanding.

But going back to the quench sequence, Can you explain a little further why the drop to 1350 for the second quench? Is this to refine the grain? Should each successive quench be at a lower temp than the previous one? If so, what would be the target temp for the final quench for 80CrV2? Is 1500 too high for the final quench? Also, does each steel type need a very specific HT or can groups of similar steels get the same HT? For example, can 1084, 1080, 1075, 80CrV2, 5160 get the same HT? I've only been at this for a little over a year so I'm still struggling to understand why things happen rather than just following instructions.


Thanks, Marc