User:Stever/Projects/rondeldagger: Difference between revisions

 

The first stage in making the replica dagger was to forge the blade, this is made from what I believe to be EN45A Steel that came from a steam train suspension spring that had broken in use. It's one of the harder metals to forge that I've encountered so far and has a very high hot-hardness. Still [[Tools/forge|our forge]] was able to heat it enough to make it workable and over the course of 2 days it was forged into the shape of the blade blank and with a long tang to fit it into the handle. The very high silicon content of the metal which makes it so hard to work also had advantages here as it helped it to resist oxidization and prevented it from loosing too much carbon to harden later.

With most of the parts now made it was time for a test assembly. The first stage of the process was "burn-in" the tang of the blade by heating it up to about 400C and then pushing the handle over it until the heat burns the opening wide enough for the tang to fit snugly. This had to be done before the final hardening of the blade as otherwise the heat from this process would ruin the temper of the blade and make it impossible to sharpen properly.

 

 

New tank fabricated it was back to the forge for the blade to be normalized and straightened (and re-normalized, and re-straightened, and re-normalized and..... you get the idea). Once the blade was stable and relieved of all internal stresses it was put through a process of grain refining which changes the structure of the metal to adjust the size of the crystal grains within it. Doing this maximizes the strength and toughness that can be achieved without lowering the final hardness too much. In the final forging process the blade was then heated to 900C, held at that temperature for a couple of minutes, and then plunged into the oil. After hardening the blade was cleaned up and the scale removed using the [[Tools/polishingwheel|buffing wheel]] before hardness testing. Testing it with the [[Tools/hardnesstester|ultrasonic hardness tester]] revealed a final surface hardness of around 53HRC which is a good hardness for this type of blade being hard enough to take a good edge but still tough enough to withstand hard use.

[[File:mountedview.JPG|left|300px|The assembled dagger]]I designed the shape of the mounting board in OpenSCAD with convex rounded top and bottom and gently concave sides, then [[Tools/laser|laser cut]] that shape out of some scrap polypropylene that was laying around in order to use as a template to help shape the board. I screwed the template onto the back of the board and then it was back to the router table to use an edge-follower bit to cut the timber to shape, this actually took 2 tries as the first time I did it one of the joints exploded apart and flung a bit of timber across the room, fortunately the board I made was large enough for a second try. Once the shape was properly cut out I changed the bit to an Ogee cutter and put an elegant curve into the edge of the board so that it would resemble the kind of mounts that are normally used for trophies or ancestral weapons. The board was then coated with 3 coats of a water-based polyurethane varnish with sanding in between coats, this didn't give as high a shine as I was hoping for but with a little wax polish it still looks pretty good. Next time I'll probably try using either Tung oil or french polish to get a higher shine.