Have some fun and make this ancient Japanese spear plane, a yari ganna!
- 1' (300mm) of square tool steel bar stock
- 1' x 2" x 1" (300x50x25mm) hardwood
- wood glue
- boiled linseed oil (or similar protective finish)
- a forge and workshop, plus common tools
Step 1: Forge the Blade
Refer to diagram, and proceed as follows:
- Heat your steel up to a bright yellow/orange (working temperature) for the first two inches
- Strike on three sides to produce a tip
- Heat between one and three inches from the end to working temperature
- Use a chop or chisel to narrow a circular neck area at two inches
- Heat first three inches, and leave to air cool until back to cold colour
(This is normalizing, and helps relieve stress from working)
- Heat between two and four inches from the end to working temperature
- Taper back from behind the neck, drawing two inches of bar out to a six inch tang
- Heat at end of tang and chop off
- Heat all of blade, and leave to air cool until back to cold colour
- Heat tip and shape to a pointed leaf shape (see photos throughout instructable)
- Heat again and add bevels to edges of the tip
- Heat neck and angle tang up about 15°
- Heat all of blade, and leave to air cool until back to cold colour, at least twice
Important - only work the steel while it is between orange and bright yellow/orange, to avoid cracks, and don't heat more than bright yellow/orange to avoid burning off carbon and melting!
Step 2: Grind and Heat Treat
Use a belt sander or grinder to flatten the back of the blade, and smooth the bevels until the edge is almost sharp
Harden: Heat from neck to tip until uniform bright yellow/orange (careful not to overheat narrow edges and tip), and quench in oil, stiring round for at least two minutes before leaving to cool enough to touch
Warning - the blade will now be brittle, so don't drop it or knock it!
Descale with a wire brush if desired
Return to belt sander to check back is flat, and to sharpen the beveled edges, cooling regularly in water so it never becomes too hot to hold in the hand (this would ruin the hardness, and cause the steel to 'blue')
- Place the iron in a conventional oven at approximately 200°C
- Examine iron after 20 minutes
- If a colour change to light straw not seen, raise temperature by 5°C and go back to step 2.
- Leave in oven for two hours at the same temperature
- Turn off oven and leave iron in until fully cooled
Tempering reduces the brittleness to a sensible level, whilst retaining sufficient hardness for the tool
Step 3: Hone the Edge
Use your preferred sharpening system (diamond whetstones and strop shown) to hone a sharp edge to the blade
Warning - This is now a very lethal weapon, so do take care to avoid injury!
Step 4: Handle Part 1
We want to set the tang securely in a wide handle, and the best way I found was to rip the handle material in half, recess each half for half of the tang, and glue the halves around the tang.
Firstly saw the wood in half, length-ways
Plane the sawn edges flat and smooth, so that they meet perfectly
Step 5: Handle Part 2
Recess for the tang:
- Draw the outline of the tang on one half of the handle
- Create a tight recess for half the tang thickness
- Place together with second half and secure tang in position
- Remove first half and draw tang outline on second half
- Create a tight recess for the second half of the tang
- Perfect recesses, such that the handle can just about be closed around it with moderate clamp pressure
Step 6: Handle Part 3
Apply glue to the two halves of the handle and clamp around the tang, and allow to dry
Step 7: Handle Part 4
Shape the handle:
- Use a plane to round over the cross-section of the handle, so that it's comfortable to hold
- Plane away material behind the back of the blade, so that it doesn't protrude below the level of the back
- Chamfer all sharp corners
Step 8: Finish and Use
The finished handle should be protected with boiled linseed oil, or similar.
I also coloured mine, before protecting, and you can see that in the video.
It's ready to use, and what a joy - not easy to get the hang of, but every so often a perfect, continuous shaving rolls off the edge of the blade :-)
Thanks for reading my instructable
Please vote for it in the Build a Tool contest - if you like it of course