10 May 2012

Personal Knife II

  Construction always starts with material. For this knife I was going as thin as practical, a ten inch circular saw blade without carbide teeth provides the stock for the blade. Micarta scavenged from the dumpster of a local plastics shop, epoxy, brass machine screws and brass tube from a hobby store are used for the handle; two thicknesses of kydex, cord and more brass tube for the sheath.
     A pattern is clamped to the blade stock and the profile scribed onto it. After that the shape is cut out with an angle grinder fitted with a thin cut off blade. Next the blank is ground just to the scribed line on the belt sander. This has to be done carefully because when the line is passed the eye is fooled into thinking its just at the line and you will be removing material that should be left on the blank.
    The belt sander can grind everywhere but the curve in the handle where the blade drops. I clean up this area with a half round file. A smooth transition without a dip is what I aim for here. The choil notch is filed in with a 1/8" round file to half its depth.

   A simple two-brick furnace with a propane torch is used to anneal the blank. This is soft fire brick that I got by tearing apart an unwanted potters kiln. The knife is brought to a bright cherry colour and then buried in the ash of the wood stove that the furnace sits on. The top and bottom bricks are hard fire brick that hold the furnace together.
     The annealed blank is now soft so the pin and thong holes are drilled. Micarta handle slabs, brass hole liner and machine screws along with the matching tap are readied to fit the handles prior to finishing the blade.

   I used to use brass tube for pins and never had any problem with them but I was looking for a mechanical lock for the handle in addition to the epoxy. Not wanting to buy handle fasteners and finding them to be too much work to make (and not coming up with a serviceable fastener), I finally thought to use just screws driven through tapped holes in the tang and the handle slabs. Testing proved that the screws would hold the handles on without epoxy.
   The sides of the blade need to be sanded clean and flat. This is done by using a flat piece of stock with sandpaper stuck to it, I have made these sanding flats with 60 grit and up to 600 grit but rarely go beyond 220. A working knife is going to need to be cleaned and the blade will get scratched up anyway. The blade is clamped to the bench on top of a spacer to elevate it above the bench surface. Then the sanding flat is held in both hands and placing it flat on the blade moved back and forth along the blades length. 
   Great pressure can be exerted but care must be taken to keep the sander flat on the blade or the edges will be rounded. I am aiming for a flat surface.  I have found this to be faster (and safer) than a belt sander that always seems to round over edges.
   One handle slab is clamped to the blade and the holes are drilled, after the first hole is drilled a tight fitting pin is put through the hole so the pieces cannot shift, the next hole is drilled and pinned. This is repeated until all holes are drilled.
   With the handle still tightly clamped to the tang the tap is wound through the previously tapped hole in the tang and threads cut into the handle, as each of the holes are tapped a screw is threaded into it and the clamp moved close to the next hole and the tap run through until all are done. A pencil is run around the tang to mark the handle so the access can be cut off and the whole procedure repeated on the other handle slab. The knife is then dry assembled to ensure that everything fits.
   After the handles are trimmed one handle has its ends finished. The end facing  the butt is trimmed so that the point of the tang is exposed. Then the handles are attached together with screws through the tapped holes and the ends of the untrimmed handle brought to match the trimmed one. The ends are are finished now as it is much harder to do after glue up.
     Back to the belt sander to grind the bevels. Scandinavian bevels are quick to grind because the minimum amount of material is removed. I use a bevel gauge to check the progress as I grind. First one side and then the other, check with the gauge, adjust my hold and grind again. Eventually the angle is correct and I can concentrate on holding the bevel flat on the belt. Having the bevels centred on the blade is important so I keep checking by sighting down the edge and applying more pressure or the amount of time I favour one spot. The aim is to leave a thin line down the centre of the blade to be removed after heat treating.

   Heat Treat
   The knife goes back into the furnace and the torch fired up. I turn the blade over in the furnace a few times to heat it evenly then watch it heat up until it glows a bright red/ orange colour bring it out quickly, check it with a magnet if it dose not stick its quenched in previously heated oil, tip down and moved with a back and forth cutting motion through the oil, after about 30 seconds the excitement is over and I pull it out of the oil, it should be black and grey with scale flaking away on the hardened area.
   Heading to the vice I wipe it off and lock it into the vice spine up. Taking a file I attempt to file the spine, the file may take off some scale or decarbonised skin but then will skid over the spine without cutting if the blade has been hardened. I then flip it over and check the full length of the edge.If all is well it goes back into the hot oil for tempering.
   The oil is brought up to 190 degrees Celsius and held there for two hours with a propane torch or camp-stove.Temperature is monitored with a meat/candy thermometer I bought from a restaurant supply store. This is fairly boring and one has to keep there wits about them as hot oil is extremely dangerous if spilled. Outside is the best place for this.
   When the two hours is up I cool the blade by quenching it in water, polish it the same as I did before heat treatment and then soft draw the back and spine with a torch an a bucket of water or snow as the season dictates.

   Glue Up
   Before I can glue up the knife its back to the sanding flats to brighten up the blade. All the parts are cleaned with alcohol and readied for assembly, epoxy is mixed, screws coated holes wiped with a toothpick dipped in epoxy, screws wound into one handle. The tang and handle slab coated with epoxy. Carefully the one prepared handle slab is lined up and the screws started into the holes in the tang making sure that they are tight and an extra thread is not left between the handle and the tang. The other side is attached with the same care. After the handles are secured the thong tube is carefully driven into its hole and epoxy wiped out of it. Epoxy squeeze out is wiped off especially around the front end of the handle where it meets the blade An alcohol whetted rag works well here as this is a pain after it sets. The knife is left somewhere warm overnight (epoxy cures better in the heat).
     Handle Shaping
    I start by sawing the screw heads off then on a disk sander I grind the screws flush to the handle material. Now that the handles are flat I can bring them flush with the tang using the disk sander and files for the concave parts. Micarta burns very easily so fresh disks or belts are necessary. The heat generated during sanding needs to be dissipated either by quenching or letting the knife cool, it should never get to hot to hold in bare hands, the epoxy can let go if heated to high.
    I then taper the handle from thick at the butt to thinner at the handle. Once this taper is even and symmetrical I dome each side by rolling the handle against the disk sander. It is important to keep working from side to side and constantly check for symmetry.
    Moving to the vice the edges are rounded and blended into the flats top and bottom of the blade then the butt is rounded nicely and the exposed tangs edge is eased with files and sandpaper.  There will be no sharp or harsh edges left, the knife should slide through your hand. After the thong hole is slightly countersunk I sand the entire handle with 180 grit paper until all other marks are gone.
For a working knife like this that's all the handle needs.
   Finishing The Knife
   The knife has yet to be sharpened there is still that little flat along the blade that has to be removed. I belt sand the bevels again this time being very careful not to overheat the steel, bare hands are the way here. Much care is used to keep the bevels even and just come to a sharp edge. When I cannot see a flat any more and feel a bur along the edge I stop grinding and move to the sanding flats.
    Starting with 120 grit paper I set the bevel flat on the paper and move it back and forth along the bevel in a sort of sawing motion. I do this on both sides switching to finer grits when the bevels reach a consistent sheen. 600 grit paper usually leaves an edge I can shave hair off my arm with.
Putting a scraper on the back of the blade is something I find very useful. This  saves the edge from being used as one and utilizes the back of the blade without hindering your ability to push against it with your other hand when carving. If you have ever sharpened a cabinet scraper you know how this is done.
    With the knife held edge down in the vise and its tip just above the jaws the spine is polished with a 220 grit sanding flat. Then the back edge of a chisel (or any smooth object harder than the knife) is placed on the spine of the knife at about a 10 degree angle and with a fair amount of downward force pushed along and slightly across the back. This deforms the metal into a bur along the side of the blade. A number of passes may be needed to form the bur. It should catch a fingernail slid up the side of the blade. 
 Both sides are done. Being careful not to slip as I’m holding a sharp tool and working on one also.
   Testing the scraper on a piece of hard wood to make sure it is formed properly. It should produce curls of wood not dust.
   The scraper will have to be sharpened occasionally just like the knife and that involves sanding/polishing off the bur to a nice square edge and forming another one. This is another reason to not polish the blade.
    So now I have a knife but no way to carry it. 
    Next the sheath.

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