1. Numerical control positioning and dotting method of laser focus
Numerical control positioning and dotting method: use a flat and clean white cardboard, lay it on the workbench, set the laser cutting head above it, and the height of the focusing mirror from the cardboard is about 10mm smaller than the focal length of the focusing mirror. For example, if the focal length of the focusing mirror is 127mm, set the focusing mirror at about 117mm from the cardboard. The NC system sets the cutting head to move every 10 mm along the X axis or Y axis, and the Z axis rises by 1 mm each time. The distance for 20 consecutive moves can be set. Each time it moves to the position, a total of 20 holes are drilled with 20 times, and the Z-axis height increases by 20mm. By observing the 20 holes, it can be found that the diameter of the holes changes from large to small, and then from small to large. Find the position with the smallest aperture is the focus position, and record this. When measuring at this position, the distance between the cardboard and the lens is the actual laser beam focus position.  
2. Inclined focus burning method
Inclined focus burning method: This method is shown as follows: place a straight board on the workbench at an angle of about 10 degrees. Set the cutting head at point A. The height of point A to the focusing mirror is 20mm smaller than the focal length of the focusing mirror. The CNC system sets the cutting head to move horizontally and continuously along the X axis or Y axis for 230mm. When the movement starts, the laser outputs 200W continuous laser. When the cutting head stops moving, the laser also stops. At this time, we can see that there is a burning trace of the laser beam on the board, which has changed from wide to narrow. Take the narrowest part of the trace as the focus position, record this point, and measure the distance between the wood plate at this position and the lens, which is the actual laser beam focus position.   
3. Laser cutting direct burning method
Direct burning method: this principle is to hold a straight wooden board, immediately form an angle of 85 degrees on the cutting worktable, and raise the cutting head to the position where the focus lens is about 1.5 times from the worktable surface. Open the laser shutter, output 200W laser beam continuously, move the board horizontally and quickly to the bottom of the focusing mirror, and you can see that there will be a burning trace on the board surface before and after the laser beam focusing from wide to narrow, and from narrow to wide, which is very close to the change of the laser beam focusing process. Take the narrowest part of the trace as the focus position, record this point, and measure the distance between the wood plate at this position and the lens, which is the actual laser beam focus position. Because this method requires manual operation, special attention should be paid to safety to avoid human injury.