This is what I have on my workbench right now. I’m pretty pleased with how they came out because they’re all my metallurgy. There’s still plenty of time to ruin them, though.
The bars that I showed in my earlier post [stderr] have been hammered out into blade-shaped things, and profile-ground. Mostly, I designed the shapes in inkscape – it seems to me that knives like bezier curves – I print the design, transfer it to a piece of vinyl flooring, then transfer that to a piece of metal. The vinyl flooring trick is something I came up with for leather-working: you can bend and fold it about like real leather and it’s thick enough to make tracing a snap. Vinyl flooring is designed to last for a long time, and be flexible – so you can make a template and throw it on a shelf and years later it will still be perfectly usable. It also marks up great with a sharpie – I just scribble production notes right on the template.
I’ve also become a big fan of a diamond-edged cutoff blade, for turning a bar into a basic shape. Here’s another trick: I paint my billets with a quick shot of grey primer so I can see the outline better and so it doesn’t rust while it’s lying around the shop.
Remember this piece of steel?
I mashed it flat with the hydraulic press at about 2000F, then hammered it as flat as I could get it before I took it over to the surface grinder.
That was surprisingly little work: about 5 minutes of cutting. It’s still 1/8″ thick and needs a lot of thinning and more shaping. When you’re dealing with composite steel, you don’t get it very thin before you quench it – sometimes the inner tension created by the quench can cause pattern-welds to bend or even pop apart. If you’re familiar with a Prince Rupert’s Drop of glass, it’s a similar thing: the thinner part of the blade may have quenched much harder than the back, because there’s more metal on the back and therefore more thermal mass.
When I do the shaping, I just eyeball everything. The sweep of the little blade seemed to want to be a bit upturned, so I went with it.
That’s what’s sitting on my bench right now. When I get the forge re-assembled and can heat-treat them, I’ll mark and quench them then start seeing about putting bevels on them, and polishing the edges until they can cut. The scratch-marks and stuff like that will get polished out when the bevel is ground.
All three blades are 15N20 and 1095 High Carbon steel, forge-welded with various transforms (mostly a good beating) from me. The middle – longish – blade is built around a core of Hitachi Blue Paper #25 steel with layered 1095 and 15N20 on the sides.
Question for the physicists in The Commentariat: What are the considerations about what makes a knife cut well?
I’ve seen a lot of claims that I think are questionable, including that the increased friction of a longer beveled edge will make the knife “stick” in the cut more.
It seems to me that what’s going on is that the knife cuts because it’s got a mechanical advantage – think of it as levering two pieces of stuff apart:
Those dimensions are approximate. But if I remember from high school (around 1975) this would have a mechanical advantage of about 3 (3:1). A shorter bevel would have less mechanical advantage and therefore would not be as good at separating two pieces of stuff. If the rise was about 1/4 of a unit, then the mechanical advantage is 12 (3:0.25) – the knife would cut much better.
Is that correct?
There are other factors: friction and whether there are significant surface material properties on the very edge of the blade. I.e.: a serrated edge or a micro-serrated edge are going to work better because they increase the length of the blade surface passing along the object being cut. Curved blades seem to cut better because they are slightly longer, but for some applications a curved blade does seem to work better – i.e.: slicing vegetables. Although I think that’s a factor of how the cutter uses the blade. There’s also the problem that some blades are shipped with a longish-seeming bevel, but the edge is ground at a sharper angle, reducing the mechanical advantage – I don’t know why anyone does that unless it’s that knife companies’ lawyers tell them “make it dull, like our customers.”
This seems to me to be one of those questions where the different sciences might give different answers. I assume a topologist would tell me that my knife is indistinguishable from a plate of pasta, or something. Knife-makers are full of stories about what makes an edge cut better or worse but to me it always seems to come back to mechanical advantage.
Unrelated: when I get some time I’m going to make some billet with 1095 that has cable damascus sides. I plan to make a pretty large chunk so if any of you are interested in a chunk of damascus billet to beat on, I’m tentatively willing to provide and even rough-cut it if you can send me a picture of what you’re looking for (please, no katanas…) When it comes to stuff like cable damascus I am now set up to produce it at nearly zero cost (I just let one billet soak in the forge while I am working on another)