Puukko Knives

Project: March - August 2021

Writeup: August 2021

Together at last...

These are a pair of general-purpose knives in the style of a traditional Finnish "Puukko". I'm not sure if the leather-stacked handles are technically traditional, but I think they work thematically (you sometimes see stacked birch-bark used). I like the simplicity of the design, and they're a good size for everyday use.

You know I'm trying when I make a scale drawing...

I made two to try out a couple of different things on each one, but they both have the same blade shape. The cross-section is almost like a diamond, but with the center line closer to the spine which leaves the spine flat on the top for handling. It actually wasn't too tricky to cut using a filing jig: you start at the edge and set your primary bevel, then turn it over and just bring the back bevel in to meet it. There's no ricasso, so you can just carry the bevels over the line where the bolster will sit (see below).

After initial hand-sanding. No, I still can't do trigonometry without drawing a diagram every time.

I was being over-cautious here and left the edge way too thick. I've never had an edge crack on me with my current process, so recently I've been fine taking things down much closer to final thickness before hardening. But the geometry looks good! I was using sandpaper glued to a rigid steel backer to keep the lines crisp.

My original forge in action! Made from an empty helium canister.

The first blade was completed before my muffle furnace was ready, so this one was hardened using my propane forge. I've got it down to a fine art now, but this blade is about as big as you could do reliably with this setup: the hotspot in the forge is so small that you have to constantly be moving the blade to heat it evenly.

This is where the fun begins...

Remember earlier when I said the lack of ricasso makes the blade easy to grind? Well now you have to fit the bolster to a five-sided blade! I didn't appreciate the difficulty of this step in my non-existent planning phase, and it took a few tries to finally get it right. This successful attempt was done by filing the bolster to allow it to fit over most of the tang, undercutting the hole with a dremel, then bashing the whole thing down onto the shoulders of the blade. The brass deforms perfectly against the contours of the hardened steel and seats itself. It also slides on and off very easily, which is nice for finishing.

Multi-layer cow and epoxy sandwich

Here you can see the blade and bolster both finished and the handle being fitted. I made the clamping jig to help with compressing the leather, but I think it mostly just got in the way. The bottom bolster is also friction-fit onto the tang and provides all of the compression needed. Once the glue is dry it's just a matter of carving the handle shape. My first effort wasn't perfect visually, but it feels great.

Shiny!

Overall I was very happy with how the first one came out. The secondary bevel wouldn't have been so high if I'd thinned the edge down further - but let's say I did that on purpose for durability...

Pre-rounded for accuracy

The second knife is largely the same, but I experimented with a stonewashed finish instead of the high-polish, textured bronze bolster and black leather. Here you can see me not being lazy and actually cutting leather ovals instead of just using squares. I cut them using a series of homemade punches made from steel tubes. Saved a whole load of time with the handle shaping. This one was also hardened and tempered in the muffle furnace.

Bronze left, brass right

Here you can just about make out the hammered top surface of the bronze bolster (it looks better in person) which just makes finishing a lot easier because you don't have to worry so much about scratching the blade while polishing. The difference in blade finish is also visible here. The stonewashing was done by dipping the finished blade in ferric chloride then shaking it in a bottle of rocks. It's certainly easier than sanding to fine grits, but I think I need to experiment with getting the oxide to stay darker. Will be interesting to see how they both age with use.

Deep, penetrating black courtesy of homemade vinegaroon dye again

Not much to say about the sheaths other than I think I got super lucky when making the pattern: I love the shape. It all seems like it's too small while you're sewing it together, but then you wet everything and slot the finished knife in and it all stretches and flows around the handle then hardens up and fits like a glove. Very satisfying. I also need to work out how to get the handles themselves to shine up nicely: they're all burnished like I usually do, but they don't seem to want to stay glossy. Maybe they need sanding to a higher grid before finishing? Anyway, I suspect this will also happen over time with use.