Criteria to make a good knife
Let’s see how the blade should be designed to cut well and can be sharpened easily. To qualify it as a “good knife” is important to have the following qualities: good steel, good heat treatment, structure and appropriate edge angle. All must be present.
Besides the good steel and good heat treatment it is important that the blade structure including: the type of rebate, thickness and angles. These details will determine that the knife will cut well, for a long time and let his sharpen easily.
Almost every beginner makes the knife blades with convex sections (Figure 1). It is a primitive criteria leaf design. It is very easy to make and very low cost, more similar to a machete (for a machete, you do not need a fine cut), it is only useful for chopping and axing branches or something.
Another very common type of construction is shown in (Figure 2), which are unsuccessful knives simply because they do not cut.
Right angles are for a chisel, not a knife to cut the things we want to cut with a knife.
Often you will find a blade is made from a flat-parallel small plates, a rebate at an angle of approx. 25º and a bevel cutting edge of 55-60º, even up to 70º in some cases. You should be reject the acquisition of a knife of these characteristics… it is useless. Another widespread type of blade is made in a flat-parallel small plates with a small concavity as shown in (Figure 3).
When it is new (see position A) it will cut relatively well until the wear and tear from use and the resharpening transform it to position B, where we find a piece similar to the case of Figure 2 with a cutting angle excessive for a knife blade.
So here we are eliminating many grams of useless steel.
Creole blades with section illustrated in (Figure 4) have good performance at the beginning (position A), we use a section something thicker at the cutting edge (position B) which is going to be difficult for resharpening because it increases the worn surface, and so requires “lowering” the blade.
I made blades of Creole style with a slightly concave to reduce this problem.
We have finally the (Figure 5), where we see a blade of unusual section. This blade enhances the cut because it offers no resistance to penetration (position A). Think of a wedge, if it is thick and the angle is large, the effort to achieve the penetration should be greater.
In the figure we see that the blade is a strip approximately 15 mm wide (parallel to the cutting edge) and 0.5 to 0.6 mm thick.
The thickness of the blade in the cutting edge area, should be 0.4 to 0.6 mm, maximum 0.7 to 0.8 mm depending the abuse that is intended to submit the knife and with respect to cutting angles aproximdadamente 20 º for general use. Minimum 15 and maximum 25 º.
If this is a knife to cut very thin cold meat the angle can be reduced to 10 degrees or less, but limits its ability to cut something hard.
In closing let me share my attributes of a “a good knife”:
It should be lightweight (unless it is one of those 4×4 knives which clearly we have for abuse, axing, hitting, breaking everything).
For this case the weight of the blade should be appropriate to the demands we’re going to submit. The weight should never be in its handle.
The weight of the handle should not be larger than necessary. It must be able to control everything that can be done with the blade. Any excess is useless, and can be harmful. Its hardness should be optimal (60 RC) for a Durable cutting edge, without being difficult to resharpen with simple elements (flatstone, steel sharpener, etc).
And preferably the blade steel should be corrosion resistant.
There are many concepts or criteria to evaluate or qualify a good knife and these are the ones that I think are the best, but nobody can affirm that really they are.