Saturday, February 21, 2015

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.



 

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