Saturday, February 21, 2015

BC8 BUSHCRAFT KNIFE - LAYOUT & PROFILE

The BC8 is for the Canadian Knifemaker Forum Spring 2015 KITH (Knife In The Hat). This is intended to be a Woodlore style bushcraft knife, with palm-sized blade and flared handle. I am trying out two sizes: 7.5" and 7.875" overall length.
After transferring the printed template to some thin plywood, I cut them out and shape them on the disc sander.
Some rummaging through my steel stock I settled on some CPM154 of 5/32" thickness.
Here I am sizing up the pattern to get the best fit. Quite a bit of material will have to be removed. Placement of the pattern helps with how much cutting and grinding have to be done.
I place the pattern close, about 1/16" to 1/32" away from edge and clamp it in place. Then I trace the pattern with a fine Sharpie. You could use layout dye and then scribe it, but I've found Sharpie holds up to the heat and water (cooling).
Here I am shaping the profile with a 60 grit ceramic belt. I like to bring everything super close to the line at this stage.
Here is the profile. Next we need to clean up the steel and surface it to remove any mill scale and surface inclusions.








BC8 BUSHCRAFT KNIFE - GRIND & DRILL

After profiling, I went on the belt and cleaned the mill scale off the steel. This can be a bit tricky as one has to keep the surface of the steel perfectly parallel to the belt. If you hit it at an angle, you can create a ton of work trying to get the two faces parallel again. So go slow and steady. Or, use some sand paper and a block.
This is after the grinder, I  do some sanding with 60 grit on the toggle clamp. This second sanding  on the bench is done at 90° to the first one on the grinder. Once any surface inclusions are gone, we can proceed to layout.
After some felt pen planning of the plunge and arc of the grind, I applied layout dye to the soon-to-be cutting edge. In the dye, we can scribe a centre line to help us with the bevel grinding. I used a drill bit. Some guys have a proper scribe, but for pre-heat treat grinding I don't think a 128th of an inch is a problem.

To use a drill bit in this fashion, you must choose the correct bit. A bit that perfectly matches the thickness of the stock. Once we have the best match for a bit, we can scratch a line along the cutting edge. Use a very hard, flat surface and keep the drill bit and knife perfectly flat as you scratch the line. Then flip the blade over and scratch another line. If everything is perfect, you get a single line. That's rarely the case. I usually get two lines, extremely close together.


I made a simple block of 3/4" plywood that has an 11° cut on one side. As I am not yet proficient in freehand grinding, I use this jig along with the tool rest to make a consistent angle.


With a Scandi grind the block only helps so much. You have to slant the knife each pass as the belt nears the tip of the knife. This ensures the grind follows the arc of the cutting edge.
 Now on to the layout. For this knife, we need a lanyard tube so we can string some parachute cord through the handle. I've chosen some 1/4" (Inside Diameter) brass tubing.
With a bushcraft knife, the single bevel means that sharpening generally cannot conflict with the handle. I've drawn a line to indicate where sharpening will be happening. 
 For layout of the pins, I chose 1/2 way and made a series of marks.
Now we have the pin (and tube) marks in place we haul out the wee anvil.
 With a centre punch, I stamp the starting holes.
A few drops of cutting fluid and we're off. I don't use fractional bits here, rather I use the numbered bits #12 and F. These are slightly oversize but correlate to the fractional bit 3/16" and 1/4" respectively.





A note on cobalt bits. If your bits don't do this, consider some cobalt bits. They are expensive, but worth the money as you can sharpen them again and again and they are still cobalt.
 The main holes are drilled.
Now to add some "adhesion" holes. Their purpose is two fold; they increase the bonding surface areas for when we glue the scales on: secondly; they reduce the weight in the handle end of the knife.




Here I am checking the lanyard tubing to see it fits into the F bit sized hole.






This is where we are at.












 As a wee bonus, I did some filework on the spine.



 

BC8 BUSHCRAFT KNIFE - HEAT TREAT

After giving the knife some additional sanding to smooth out the major scratches, I cleaned it with acetone and placed it on a piece of stainless steel foil. I am not worried too much about the bevel as I will complete the grind after heat treatment.

The foil is wrapped up to make an envelope which prevents excessive oxidization of the blade during heat treatment. The foil I use is 304 stainless steel foil wrap from McMaster-Carr, P/N 3254K22.
I fold the long edges together and press them with a block of wood.
Then the ends are folded up.
And finally another set of folds.









And into the oven. I ramp it up and soak it at about 750°C for 10 to 15 minutes, then continue up to 1060°C for a soak of 15 to 20 minutes.
This is the blade inside the envelope fresh from the oven.
I plate quench with two copper plates. I  have turned on the tempering oven and set to 200°C (400°F)
Now to open the envelope and take a look. Hopefully nothing is cracked or warped.
Ta da!
Once the blade is cool enough to hold, I place it into the tempering oven for two hours at 200°C.
A very simple solution is to use a countdown timer, set to 2 hours.

BC8 BUSHCRAFT KNIFE - SCALES

For the post heat treatment finishing, I used my toggle clamp and a range of sand papers. Starting at 180 grit and working to 320. The sharp spine edge of a bushcraft knife is important for scraping and a flat block is necessary for keeping the edge sharp and not rounding it.
After some finish sanding I went over to the grinder with a fresh belt and worked the bevel very slowly. Cooling in water every pass. At this stage I don't want to kill the hardness by burning the steel.


For the scales I wanted to go with something natural. For me, Micarta or G10 seems so in-congruent on a bushcraft knife. The first part of putting scales on is to get the book matched pattern right. Make sure that the two sides you want showing line up properly.


Trace the handle shape and roughed them out on the wood band saw. I used a roll of masking tape to trace the curve at the scale fronts.
Here I have one scale clamped and drilled. Using slightly over sized numbered bit 12 and F will allow an easy fit and some epoxy to flow around the pins.
After drilling both scales on the drill press I use wooden dowel to pin them together. Now we work on the fronts.
I sand them with 120 and then a really fine belt, say 600. Keep the fronts square (90°) to their faces. After the finishing belt let's give them a buff.
On the buffer, I used just a little black compound, then over to the clean cotton wheel for a shine. This is our last chance to perfect these areas.
 The maple burl looks sweet!
Cut the pins and test fit. I also drill some tiny holes or scratch up the insides of the scales so they have more surface area to bond with.
 For this 'special' knife I am using two 3/16" mosaic pins, one 1/4" center mosaic and one section of brass 1/4" tubing for the lanyard hold.
Everything's ready to go for glue up. I will be using Acraglas. I put on some disposable gloves and prepare the bench for messy work. A plastic shopping bag or piece of craft paper work fine for protecting the bench.





I used cheapo vise-grips with leather pads (see Shop Jigs & Fixtures page) to hold the scales down. Sometimes you need to flex the wood in certain places to make the tiny gaps go away.






Of extra importance is the Acraglas fill on the spine where the filework is. We are trying for no gaps, no air pockets, bubbles or anything unsightly. The filework is an eye catcher and you don't want to have a big air bubble hole in the epoxy there.