Profile and Edge Geometry Choices for a Bug-Out BladeOur guest author for the past two weeks is Todd Gdula, a professional bladesmith and member of the American Bladesmith Society. He does custom work and his website is www.toddblades.com.
Having already selected the steel type from among the dozens of practical choices, choosing a good profile and geometry is relatively simple.
Blade GeometryGeometry refers to the type of edge. There are essentially three: hollow, convex, and flat.
|L-R: Hollow, flat, and convex grinds.|
A hollow grind is the sharpest, but the most fragile. Its strength is in knives used for fine cuts. Its weakness lies in chopping, and even worse being hammered through an object.
A convex grind is the opposite of a hollow grind; the sides of the blade bow out rather than in. It is also called an apple seed grind or a Moran edge. It has the most steel behind the edge and is therefore the strongest. Axes and hatchets have this type of edge, and although it is the least sharp, it has the best edge retention. Despite the fact that it’s the least sharp it is possible to bring a convex edge to sharpness where it will cleanly cut paper.
A flat grind is just that; the flats of the blade are actually flat. It is considered a compromise between the hollow grind and the convex grind.
The hollow grind is the first and easiest to eliminate. It is simply too fragile to be used as an all around survival knife.
A good argument can be made for a flat grind, and it’s not a bad choice. For shear strength, however, it’s just not as good as a convex grind.
So, we’re left with the convex grind. I think it’s the best choice. Axes have this grind for a reason; anyone who has ever driven an axe into a log with a sledge hammer will testify to how strong this edge is. I’d make it ¼” thick at the base of the spine, tapering to the tip.
We need to choose a profile next. For a big working knife I want a blade 10-12” long and around 1 ½” wide. We have the choice of any number of blade styles:
spear point, bolo point, or drop point being among the most popular.
|Bowie (clip) point|
Bowie Point: Jim Bowie made the knife named after him famous as a fighter. It was also very popular as a camp/utility knife, used as a chopper, skinner, and steak cutter. It has a clip point to lighten the tip, making it a faster fighter but a less powerful chopper.
The bolo point adds weight to the tip and makes for the most powerful chopper of the group, but it’s front heavy and a poor stabber, and so not a great fighter.
Of the last two, the drop point is the better chopper and the spear point is the better fighter, but they’re both pretty good all around designs. I’d go with either one of these with a slight bias toward the spear point.