How to focus the laser?

Quick Answer:

Adjust the table height or move the focal tube to/from the material surface.

Complete Answer:

The laser beam is focused through the focal lens. The focal lens acts like a magnifying glass and sunlight. For a 55mm lens, the laser beam passes through the lens and converges to the smallest point at about 55mm from the edge of the lens. The laser beam is concentrated to the smallest size at this "spot". Given that the lens is mounted in the focal tube, the question is how to put the material at the optimum location to engrave or cut.

First, think of what results are desired. Whenever we want to engrave, we want to have the laser beam focused to the smallest spot and that spot located at the top surface of the material. Having the smallest spot size will give us the best resolution.. the best DPI(dots per inch). The laser machine should have come with a manual height measurement tool. Some machine come with a square piece or acrylic to match to a marker on the side of the focal tube. Other machines come with a feeler gauge that snuggly fits between the focal tube nozzle and the top surface of the material.

The normal adjustment method is to place the material on the worktable and then to move the worktable height such that the top surface of the material is at the focus spot of the laser beam. Use the measurement tool while moving the table to the proper height. Make sure not to move the table too far. You will not want to damage the table surface, material, or the focal assembly.

Most laser machines have a movable table height. If the table will not move or is already moved to the top, then the focal tube has some adjustment to move/slide up and down about 1.5 inches. First, loosen the focal tube nut(or screw). Second, move the focal tube to the desired height above the material surface. Last, tighten the focal tube nut(or screw).

You may be concerned that you are using the provided tool to place the focus at the prescribed distance, but the focus just doesn't seems right. Please remember that the Chinese optics are not the best. The optimum focal distance might be slightly closer or farther away from the lens. Place a piece of flat scrap material (wood) under the focal assembly. Adjust the focus such that the material is slightly too close to the focal lens. Use the "laser" button to make a test spot on the wood. The spot size will be larger than desire for engraving. Move the table away from the lens just a small distance. Move the wood to a clean target location. Make another test spot using the "laser" button. The spot size should have gotten smaller. Continue moving the table and making test spots on the wood surface. When the spot starts getting bigger, then you have just passed the focal point. This is the easiest way to find the true focal distance of your lens.

To get the best engraving....
1) Make sure that your laser is focused on the material.
2) If your target material is an uneven surface, then it may find some areas where the laser is out of focus.
3) If your target material is a dowel rod and you are not using a rotary attachment. The laser will be out of focus at some portions of the image..
4) If your image seems fuzzy at the edges of the laser cut, but is focused, then you might be trying to engrave at too high of a speed. Set the engraving speed to a slower rate. You will also need to reduce the laser power percentage as to not over-burn the material.
5) If your material shows (Scan) lines in the engraved areas, then the "scan gap" may need to be reduced. The "scan gap" is the amount of space that the rail moves in the Y direction between engraver scanning passes. Setting the "scan gap" to a lower number will give a better resolution. With some materials (anodized aluminum, hard plastics, and hard wood), a scan gap of 0.05 may give excellent results. A good setting for glass is 0.07. In soft plastics, a scan gap of 0.1 will be needed to ensure the plastic does not glob.. A setting of 0.1 is good for soft woods.

If you are regularly engraving materials that vary in distance from the focal point, then it may be a good idea to purchase a focal lens with longer focal length. The longer focal length will stay tighter to focus for more distance.

FAQ item was submitted:

10/16/2009 By: Raymond L. Scott

Raymond L. Scott  ... Owner Engineer
601 North Verity Parkway
Middletown, OH 45042
(513) 217-5707

Related Topics:

focus, distance, lens, focal distance