Basic Instructions For Making Your Own Bent KnifeIt goes without saying that you should definitely use all safety gear when grinding – good eye and hearing protection, and a respirator to avoid breathing metal dust. These are important – please protect yourself! It’s actually easy, you just have to do it!
First, decide all the details for your blade - length; double or single edged; bevel angle (for carving mostly hard woods
and rough carving, the edge will hold up better with greater bevel angle); bevel geometry (where the main and secondary
bevels will be). Some of these things may be beyond your scope. Maybe you can make some knives that would be somewhat
useable, and enjoy them as tools you made anyway. You’ll learn a lot with every blade you make.
Grind the profile. If you are making a double edge blade, then it should be fairly symmetrical. It’s difficult to grind the bevels for a double edge knife. You might make your first bent knives single edge.
This is important: It is ok for the blade to get hot (don’t burn yourself!), even getting red won’t affect the temper because it hasn’t even been heat treated yet. The important thing is that you should not cool the blade in water. If it gets too hot to hold, use pliers or just set it aside to cool for a while. Don’t cool it with any liquid before it's been heat treated.
Grind the bevels. The geometry of the bevels at the edges, especially the bevels on the bottom that contact the wood, has everything
to do with how the blade will function. I believe the cross section shown below is the best geometry for bent knives. The two
flat bevels on the bottom allow for good control following lines (as in Northwest Coast formline carving) and for making rounding cuts
(as for spoons and bowls).
Please Note: Only the main bevels are ground before heat treating. The microbevels should be done after heat treating, when the burrs are drawn. This is to avoid decarburizing the fine edges.
Grinding the bevels can be done a lot of different ways. For my classes, students use files. At this point (before heat treating), the steel is relatively soft and can be filed by hand (with a good, sharp file). Although this entails more “elbow grease”, it is a good way to learn the basics and to go slow. Power tools are not only dangerous, they also make mistakes faster. But if that is where you’re at, the tool most professional knife makers use is a 2 inch wide belt machine (typically 2”x72”). Alternatively to having a special machine, you could mount a hand held belt sander upside down. The benefit of any belt sander is that it doesn’t change shape (it stays flat), as opposed to a grinding wheel that changes shape as it is used. Most of the bevel shaping can be done before the blade is bent, while it is still straight. The initial grind would be with 36 or 50 grit, followed up with finer and finer belts (120 grit, then 240, then 400 if you want the bevels to end up fairly scratch free). The goal is to finish with the bevels even and uniform and the edges about 1/64" thick (about a thick hairline) along their entire length. Sound hard? It's more difficult than it sounds, but practice does make for improvement.
Bending is kinda critical, because you’ve already put a good deal of effort into the blade. If you have a small forge, you can use that at a low heat, and reducing flame. Otherwise a regular propane plumber’s torch will work. Don’t use oxy-propane (or acetylene) – that’s way too hot. Heat the blade evenly to a dull red. Avoid overheating the delicate edge(s). Gently bend to the shape you want. You can use a small pair of pliers with smooth jaws or gently push the hot blade against something rigid, like a preheated piece of metal held in a vice. Best to go slow and be careful to stay away from the edges. If you bend it too far, it’s usually difficult to bend it back. It’s easier to bend more with another gentle heat.
Heat treating is a two step process – hardening and then tempering.
Mounting the handle can be done before or after final sharpening, but is easier before the blade is sharpened. It’s also nice
having a big handle on the blade for holding it during
the final sharpening.
This is important: Now that the blade has been heat treated, it will loose its temper if it gets too hot from grinding/polishing. If you use power sharpening equipment, don’t heat the edge to show any tempering colors (especially beyond straw). It’s OK to cool with water, but best to just go slow. If you do overheat the edge, it will probably be too soft to hold a good edge. Then you’ll need to go through the entire heat treating again.
Sharpening should be started by truing up the convex side of the blade (it may have cupped or gotten misshaped during the bending)
and removing the scratches there to at
least 600 grit. This is the really critical part of the blade, as it controls how it will work. The bevel
there should be fairly flat. A little bit of roundness is better for carving hollows like spoons and bowls, to round
out through the cuts, but it should be quite flat for at least 1/4" back from the edge.
Follow my guidelines to care for your carving tools: protect from rusting and avoid contact with other hard surfaces (sand, metal, glass…). Strop often!
One of the best indicators of how much sharpening a person has done is how careful they are with their tools when not using them. A simple towel makes a temporary tool roll. Make sure it is dry!
My carving knives are intended for serious wood carvers. They are razor sharp and can be very dangerous if used improperly. Please be careful and don't allow young people to use them unsupervised.
Your satisfaction is fully guaranteed. If you have a problem of any kind with one of my knives, please let me know. I will make it right with you.