Part 1. Hook, crooked, bent knives, whatever you like to call them, are an exceptionally versatile tool if made well. Carvers, craftspeople, and woodworkers of every stripe would benefit from having a good sturdy hook in their tool box. I know many who would not be without one. A strong hook gets into places nothing else will.
It is the tool for carving wooden bowls and spoons, masks, wooden musical instruments, furniture and just about anything with an organic shape in mind.
First, the steel. Tool steel, like 01, bought from a steel supplier is annealed and easy to work with, or one can recover steel. I recover mill bandsaw blade, L6 steel or 15n20, 30 cm (12”) wide x 76 cm (30") or gang saw, 45 cm (18”) diameter x 2.5 mm (1/ 8”) because of its tensile qualities and strength. This is a high carbon steel with a combination of molybdenum, chromium, and nickel.
Carbon must be present to enable the steel to harden. Carbon hardens the steel. Nickel improves the toughness of the steel, aids in corrosion resistance, helps reduce distortion in the quenching process but is mostly for toughness. More silicon is added for durability, makes it last longer and hold tension longer. Manganese increases tensile strength and durability. Chromium found in L6 aids in fending off corrosion/rust. Chrome also improves wear resistance, resists softening in the temper process and will also increase hardenability of steel. Molybdenum, commonly referred to as “Moly” is essential for the control of the hardness of the steel when tempering.
When filers (a mill working trade) toss out band saw they cut them up into 1.20 m (4’) lengths. If you can get some it is well worth using for knife blades, especially for hooks. The exceptional tensile strength lends itself to an excellent edge. A crooked knife made from lumber mill band or gang saw blade steel is a superior knife.
To make a hook of medium size using sawblade with a 7.5 cm (3”) blade (with any hard high carbon steel the process is the same) cut a piece of steel 2 cm (3/4”) x 2.5 mm (1/8”) x 15 cm (6”). Split a piece of 6.5 cm (2 1/2") thick ceramic wool 25 cm (10") x 25 cm (10"), lay your piece of steel on half of the wool . Work in a medium lit environment. By heating with a propane torch, you can bring the length of steel to a dull red slowly over 10 minutes. Keep it at that colour for at least 5 minutes by passing from one end to the other. Bring the colour to a red-orange. Use the other half of the wool to reflect heat back onto the steel. Cover the blade with the half so that the wool completely envelopes the red-orange steel. Let it cool slowly overnight. In the morning you should be able to bend the steel with your fingers. If you can't it didn't anneal. You can repeat the process.
Now you have a piece 2.5 mm (1/8”) x 2 cm (3/4”) x 15 cm (6”) long and annealed. Dedicate the clearest side, the side with no nicks or scratches, as the back. Then designate one end as the tip end. On both sides of your blank draw a line across the middle of the blade. This is the centre line. Now there is a back and face, 7.5 cm (3") of tang and 7.5 cm (3") of blade. Now draw a line lengthwise right down the centre of the blade, from end to end. This is your length line. On the tang, 2.5 cm (1") down from the centre cross line, mark your first bolt hole on the length line. Mark a second hole point 1.25 cm (1/2”) from the end of the tang, on the centre length line. Drill both points using a 5/32” size bit. Drill over each hole 1/2 way through with a 5/16" bit to countersink #8 pan heads flush to the bottom of the tang. From the tip end, draw 2 lines, one on either side of the lengthwise centre line. Using these two lines as guides, draw slow curves along their lengths. These will be your cutting edges. Now cut out the pattern with a hacksaw and file to the curved lines. You can grind but have a can of water beside you.
Part 2 Setting the tang into the handle block..
You now have a roughed out, annealed, medium-sized hook blade form with holes drilled. Set the tang into a handle now so that working on the blade will be easier.
Cut a block of hardwood 3.75 cm (1 ½”) x 4.5 cm (1 ¾”) x 28 cm (11”). Birch works well, is easy to carve and strong enough for hook knife handles.
File the sides of the blade tang so they’re true. Place the tang on the new surface up to the centre cross line marked on the blade. Outline the tang tight with a sharp pencil. Carve the tang into the block so that the tang is sunk 1.25 mm (1/16”) below the surface of the block. You want it to be a perfect fit with depth forgiveness for later when you’ll finish the handle. Mark the bolt holes through the tang onto the wood. Drill 2.5 cm (1/8”) diameter holes straight through the block. Place your tang into the block. Screw in two 3.75cm (1 ½”) #8 stainless machine bolts and snug the blade and handle together with square nuts to make sure it fits. Now trace the nuts onto the block and countersink them 1.25 mm below the surface.
Part 3: putting the edges on.
This style of hook knife is strong. It is a double bevelled straight knife with a sturdy hook and a long handle for control. The annealed roughed out blade for the hook knife is now ready for the edges to be put on. The success of this technique and the one to follow, in part 4, depends on how well the steel is annealed.
Put the blade in a vise securely with the clearest side down. You’ll need files: a 20 cm (8") flat bastard and a 15 cm (6") mill bastard. The idea is to file an edge bevelled to the centre line, from the tip of the blade to the cross line on either side of the centre line. As you flat file down the side, leave the blade with a gentle curve up and off, starting your exit 2 cm (3/4") before the cross line. Gently drop the outside end of the file, lift up and off.
Part 4. Putting a hook on your blade.
The success of this step really depends on how well the steel is annealed. Tool steel won't give if it’s not annealed, or if it’s not completely annealed it will be stiff which is when there is the risk of fracturing or breaking the blade. Sawblade steel, on the other hand, will be a bit stiff even when it’s annealed because of its alloy content. The alloys gives saw steel some of its tensile strength which lends itself to a superior cutting edge. Set the tang into the handle, set the nuts into the handle then screw in the bolts snug and then give them a quarter turn more. For this hook use a 3 cm (1 ¼") dia. x 30.5 cm (12”) piece of hardwood dowel secured in a vise. Square the dowel on 2 sides so that it sits into your vise. For a smaller hook use a smaller diameter dowel.
(Picture of the blade being shaped on the dowel held in the vise, Pic # 10)
Place the tip of the blade on the dowel parallel to the floor. Using a small wooden mallet, begin to shape the hook with even, rapid taps, bending it evenly around the dowel. Start at the tip with a soft touch, strengthening your taps as you feed the mallet the thicker blade until the steel begins to give. Move the blade slowly into the mallet. Make sure the mallet taps are square on the blade, otherwise the razor edge will get bent, creating more work. There are as many variations of hook shapes and sizes as you can imagine.
Part 5 Hardening
While the blade is still in the handle, hone it as sharp as possible. Wrap a sheet of 600 grit wet/dry sand paper around a piece of dowel (30 cm or 12" of broom stick works well) and hone the inside of the hook. To deal with any damage to the edge and for sharpening the hook after it is hard, make two more dowel sanding sticks with 360 and 240 grit. Use dowel sanding sticks for the inside of the hook and straight sanding sticks for the back. Cone and flat stones are more expensive. If you have them, use them otherwise the sticks work great and are inexpensive. Once the hook is hardened and tempered it will be sharpened from the inside and only the burr will be removed from the back.
Take the blade out of the handle and place it on one split half of the wool. Take the other half and lay it beside the blade for heat reflection. Always be aware of the razor sharp, thin, soft edge. Warm the oil in the can to body temperature on a stove. Japanese sword smiths apparently achieved this temperature in the stomachs of slaves. An old timer told me his father would use fresh urine... from a cow. I prefer canola for the deep fried chicken aroma after dousing. Have the vise grip adjusted to hold the blade securely and ready. Do a practice run smoothly and quickly attaching grips with one hand to the end of the tang, from under the flame, off the wool to where it would land into the centre of the oil can, like a perfect dive but don’t go into the oil. When the real quenching in oil happens don’t touch the sides or bottom of the can with the blade.
You want to achieve an even cherry red in the blade down to the first bolt hole. Light your torch and start passing the flame over the blade. The cutting edges are thin and the tip is particularly vulnerable, so when passing over the blade be aware of spending more time on the thick centre.
Move the flame from the bolt hole to just below the tip. The metal will begin to turn pale straw, straw, bronze, brown, purple, blue, blue green. Spend more time at the centre line, and shadows will pass over the blade. It will begin to glow cherry red. Keep the cherry red and make it grow towards the tip, constantly evening out the colour. At this point the tip and thin edges are vulnerable. If you let it get too hot or glowing orange you're burning out carbon. At yellow you're ruining the metal and there is distortion. This situation happens very quickly so watch that tip closely. When it passes into a cherry red evenly across and from tip to tang, attach the vise grips to the end of the tang, get ready, and in one smooth motion douse it into the oil.
Part 6 Tempering a Hook Knife
If you make the mistake of drawing too much, it can be corrected. The blade would have to be re-hardened so the last step would have to be repeated. You don’t really want to do this because there would be a good chance of damaging your blade. I think the two main points are patience, and easy does it. You can do it though.
Clean the tang and the back of the blade to show the brightness of the steel. Temper in a preheated oven at 460F for about 10 minutes. Check the colour by very quickly cracking open your oven door and looking at the blade colour every 5 minutes or so (do this with goggles on or you will lose your eyelashes). It’s best to temper in a very well lit environment. Place your blade tip up in your oven on a middle rack, making sure you have a clear view of the brightness of the steel. Temper the whole blade and tang the same – the colour of straw. When it reaches a straw colour, douse it in a litre of room temperature water.
Now take some hardness away from the tang to assure the blade won’t snap at the handle. Turn a front element on maximum and place the tang end up to the first bolt hole right on the element. When the tang begins to turns blue, take the blade with an oven mitt and douse the whole thing in room temperature water. This technique is called differentially tempering.
The hardening and tempering process is tricky but you will be able to carve hardwoods like maple and oak, and fruitwoods like cherry and apple without losing the knives’ razor edge.
Scott
Materials.
-a propane torch.
-1 black marker.
-hacksaw.
a 20 cm (8") flat bastard and a 15 cm (6") mill bastard files.
-A drill press or drill.
-5/32, 1/8, 3/8 inch drill bits for steel.
-stapler.
-band saw.
-wood mallet.
-vise grips.
- stove with an oven
-High carbon steel, preferably a piece of lumber mill saw blade steel, gang or band saw.
-25cm x 25cm x 6cm piece of ceramic wool. Kiln supplies.
-a block of hardwood 3.75 cm (1 ½”) x 4.5 cm (1 ¾”) x 28 cm (11”). Birch.
-2 x 1 ½ inch #8 pan head, stainless machine bolts with square nuts. Fastener company.
- 6 sanding stick blocks: 2 cm (3/4") x 3.5 cm (1 3/8") x 30.5 cm (12"), and square with crisp corners. I wrap each with a sheet of no-fill sandpaper, starting from 100 grit, 240,360,500, 800 and 1000 grit. ( 80 cents each).
-3 cm (1 ¼") dia. x 30.5 cm (12”) piece of hardwood dowel.
-1 litre coffee can filed 2/3 with canola or olive oi.l
-10 litre bucket filled ¼ with sand.
-10 litre bucket filled with room temperature water.
