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Doug Ayen

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new knife [Apr. 15th, 2007|12:26 am]
Doug Ayen
Started a new knife today. A local blacksmithing gathering is having a forged knife competition, all materials must be "recycled." I know a challenge when I hear one. I have a couple of old broken bandsaw blades kicking around the shop, one 3/4, one 1" in diameter: the 3/4", cut into ~8" pieces, would be the subject of the first test run. The billet was about 3/8" thick.

I didn't really expect this to work perfectly the first time -- I have no idea what the alloy of these sawblades are, could be bi-metallic, could be high carbon, could even be M2. While they looked identical, I'm not even certain that both blades are the same. A quick check showed that the first sawblade was hardenable, so on the the billet.

After slicing it up with the chop saw, I had 8 pieces to use and one short piece to keep for documentations purposes. I knocked off the surface crud with a worn 60-grit belt, and assembled the primary stack. I had an idea I wanted to try out, to see if I could get a sort of wave pattern in the damascus, so I stacked with with the teeth still on, each layer having the teeth facing out on alternating sides. I knew this would be hard to get a good weld on around the edges, but if I *could* make it work, that would be neat.

I used a vice to hold the stack together, with a C-clamp to hold the very end, and wrapped the billet with soft black iron wire to hold it together in the forge. As an experiment, I made a solution of borax and water, and dipped the wired-up billet stack in the mix. In theory, as it dried the borax would be left behind, probably also with a bit of lime from the local water supply.

The forge itself was set up with the blown burner, since with that setup I can get higher temperatures faster than with the venturi burner. Since excessive oxygen in the furnace can cause excessive scale and cause problems with the weld, I tossed in a chunk of charcoal to scavenge O2.

The forge set up, the gas turned on and ignited, then the air turned on. I adjusted the forge flame to slightly oxidizing and brought the fore up to working temperature, then readjusted the flame to reducing and added the billet stack, letting the borax solution dry out, then adding more borax on the sides of the billet once the piece warmed up enough for the borax to stick, then leaving it in until it got to a nice yellow glow -- but not spitting sparks, an indication that the steel is burning. I welded the end up, removed the first wire wrap, did the next section, the next, filpped the ends, and did the last bit.

Since I wanted some documentation bits, I cut off 1/4" off one end, the end that would be the tip of the knife. Since the pieces were only roughly the same length, even welded up there was a likelyhood of cold shuts and inclusions, by grinding them even or, as in this case, cutting off the end makes it a bit more likely to succeed.

8 layers is pretty low, but this was just a test after all, not a multi-day "lets see how many layers we can make" effort. That'll be the final knife. :) Now that the billet was consolidated into a fairly solid lump, I wanted to see if I could get those alternating sawteeth to show up on the sides. To do this, I re-fluxed, re-heated, then hammered down the edges, just like forging in a bevel, until they were half the thickness of the body of the billet.

I changed from the blown burner to the venturi, set also to a reducding flame, and forged the tip and tang out; while hammering the tang, I saw signs that I had some delamination going on in the billet. I went over the billet again from tip to tant to try to ensure everything was well-adhesed, then did the final straightening, heated to critical and held a minute, then put it in the vermiculite to coold down.


Once that was cooled down, I started with the grinding. Profiling first, it was quite clear that the edges around the sawteeth hadn't welded up, except on the tang and tip. whilte still it looks possible, I didn't quite pull it off this time, and the knife, originally intended to be a dagger, was redesigned into a single-edged sheath knife. I ground in the bevels using a hollow grind on the 12" wheel, leaving a 1/8" back ridge. That revealed the biggest fault with this knife - several cold shuts, or areas that didn't quite weld into a contiguous piece of steel. Nothing on the very edge, though, and if I do a nice deep etch, those should blend in with any pattern that emerges. Even though this is all the same steel (unless this turns out to be a bimetallic blade) you'll usually get some pattern due to decarburization. If this is bi-metallic, then I should get a pretty significant pattern -- but we'll see.

I did the grinding down to the pre-heat-treatment stage, A-16 Trizact structured abrasive (roughly 16-micron, or 800 grit) and quit for the night. Not the best I've done, but not horrible either. Even with flaws, unlews something worse turns up post-heat treat, this should be a quite useable knife, and not too ugly.

Pics will be up once I find my camera usb cord.

--doug
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