Ultimately, this is a focal point. A laser is most powerful when its energy is focused on the smallest possible point. This means there is a "sweet spot" in front of the camera, where cutting and sculpting are most efficient; Anything closer or farther than that won't be as effective. For example, the distance on his machine is exactly 50.3 millimeters. The green laser pointer beam is focused through a focusing lens. Focusing lenses act like magnifying glasses and sunlight. For a 55mm lens, the laser beam passes through the lens and converges to a minimum point about 55mm from the edge of the lens. The laser beam is concentrated at this "point" to its minimum size. Given that the lens is mounted in a focal tube, the problem is how to put the material in the best position to sculpt or cut. All other things being equal, a lens with a shorter focal length will have a shorter focal length (high power density) and a shorter length (can't cut too deep), and a lens with a longer focal length will have the opposite - a larger focus and a longer length of time. Lens selection is a tradeoff between these two features, and a 2" lens (usually the standard lens you get) is a good general-purpose lens.
First, think about the desired outcome. Whenever we want to sculpt, we want to focus the laser beam on the smallest spot of light, and that spot is on the top surface of the material. Having the smallest spot size will give us the best resolution... Best DPI (points per inch). The high powered laser machine shall have a manual height measuring tool. Some machines come with a square or acrylic to match the mark on the side of the coke tube. Other machines are fitted with feelers that fit tightly between the nozzle of the focusing tube and the top surface of the material. Most lasers have a removable bench height. If the table does not move or has moved to the top, then the focal tube makes some adjustments to move up and down/slide about 1.5 inches. First, loosen the focus tube nut (or screw). Next, move the coke tube to the desired height above the material surface. Finally, tighten the focus tube nut (or screw).
Positive focus cutting refers to the cutting focus on the workpiece, the focus is located above the cutting material. For carbon steel oxygen cutting, proper use of coke. The cutting width at the bottom of the workpiece is larger than the upper surface, which is conducive to slag removal and oxygen reaching the bottom of the workpiece to participate in the full oxidation reaction. Within a certain range of focal length, the greater the positive focal length, the larger the size of the plate surface spot, the more sufficient the preheating and heat supplement around the slit, the smoother and brighter the carbon steel cutting surface. This is also called positive attention. When the workpiece to be cut is stainless steel or aluminum plate, the cutting point in the workpiece is often used. However, a disadvantage of this method is that due to the focusing principle, the cutting amplitude is larger than that of the cutting point on the workpiece surface. At the same time, the cutting airflow required by this mode is large, the temperature is enough, and the cutting and perforation time is slightly longer. So in the selection of workpiece material, mainly stainless steel or high hardness of aluminum tube.