These types of blades have a sharp edge on the leading edge of the blade and are cut by cutting through vegetation. It is by far the most common type of metal blade and is usually standard on brush cutters with metal blades. Blades come in an almost infinite number of shapes, but what they all have in common is that they are usually lasered or stamped from sheet steel. They range in shape from oblong to round and have dozens of small knife-like teeth. The most common is a star with three or four cutting edges.
Advantage
Inexpensive, due to being made from one piece and stamped from sheet steel for faster production. Usually good at cutting soft materials such as grass and waterweed. But it depends a lot on the design of the blade. Depending on the design and quality of the steel, there is usually a lot of punishment to take.
Shortcoming
As the tip of the blade becomes blunt, the efficiency decreases rapidly. This is because the blade spins so fast that only the tip of the blade can make the cut. When the brushcutter head is oscillating rapidly from side to side, the cutting edge of the blade will actually do nothing but cut. As a fixed blade, when you hit hidden rocks or steel objects, the tip will bend or chip, depending on the type of blade and the quality of the steel. This is why some three of the four blades have beveled cutting edges. Not for cutting efficiency, but for liability reasons to make the blade more resistant to breaking.
Cutting Ability
The number of blades does have a big impact on how the blade behaves. The blade relies on the sharp leading edge of the blade to cut, but since the blade rotates at around 100 to 120 revolutions per second, usually only the outermost edge does the cutting.
Now, if you can imagine your mower head oscillating from side to side, the speed of the oscillating motion will determine how much the blade is exposed to the new grass. The swing is very slow, and only the tip of the blade can make the cut. Swing very fast, more tips mow.
Now consider a rectangular blade with two cutting edges, which rotates at 100 revolutions per second, which means that one cutting edge passes the same point 200 times in one second. Let's say you swing the brushcutter sideways 1 meter in 1 second. This means that only the outside 5mm of the blade can actually cut new material. With the 4-edged blade, only a 2.5mm outer edge cuts, while the 8-edged blade only cuts through any grass with a 1.2mm outer edge.
So as you can see, the blade doesn't actually do any cutting. Now moving on to the 40-point blades, each cutting only a fraction of a millimeter. So, as with nylon wire, only the outermost end of the blade actually does the cutting.
This little blade dulls quickly, so it ends up shredding vegetation, which means the blade quickly becomes a shredding blade. Only when this happens and rough uncut vegetation springs back under the blade, or when cutting in a vertical motion, will the inner blade make any cut? Dull blades are one of the main reasons users get into the habit of turning their brush cutters up to full speed and throwing the blades into heavier vegetation, a habit that can be hard to break when switching to chisel or saw-type blades.
Multi-tip blades become less effective the faster the tip loosens, but at the same time, due to their more rounded shape, drag grass to the outside of the blade and are therefore less likely to cause long strands of grass to wrap around the gearhead.
This is why different blades are better suited for different types of vegetation, and why many brush cutters come standard with a range of blades.
Mulching Ability
Likewise, rectangular and star-edged blades are best for mulching when the blade is cutting vertically through vegetation, as these provide the largest cutting edge area for vegetation.
A more rounded shape, multi-point blade with a shorter blade is of little use when it comes to mulching.
Chisel Blades