Laser head specifics

[Yaro]

Hi all,

I want to ask if someone have more specifics(and more experience) how to build a good laser head. In particular i have this questions:

- Difference between 20mm and 25mm optics?
- The best focus that i can use for cut and engrave without change every time the lens?(or what is better focus lens?)
- Output nozzle hole diameter?
- Distance between output nozzle tip and the workpiece?
- o-rings need to be termal or the temperature of the optics is low?
- what pressure of airflow is better?
- the diameter of laser beam for a 40w 60w and 100w where i can find them(are the same for each manufactor?)? It depends on the distance from co2 laser nozzle?

[cvoinescu]

I can't answer most of those questions, but this might help: there is no one "better" lens in general.

All else being equal, a lens with a short focal length focuses to a smaller spot, but has a shallow depth-of-field (meaning that the narrow spot is achieved only over a small vertical distance). This means that it can engrave flat materials accurately, and can cut thin, flat materials with a narrow kerf, but is not suitable for cutting thick material, because the beam disperses too quickly.

A lens with a long focal length does not focus as narrowly at any distance (because of difraction), but it has a reasonably small spot size over a much larger vertical distance. It is more suitable for thick materials, and for objects that are not perfectly flat. However, it cuts with a wider kerf, so it's not as good for thin materials (slower cut, more burning).

The most commonly used focal length is a compromise, between the two extremes. For lasers this size, 25 mm is "short", 100 mm is "long", and a 50 mm (2") focal length is somewhere in between and gives decent performance in many applications.

[TLHarrell]

- Difference between 20mm and 25mm optics?

This merely refers to the diameter of the mirror or lens. One is a bit bigger than the other. This will not affect cut speed, quality, or anything else. It will reduce the possibility of clipping the edge of a mount with the beam. For tubes above 40 watts, I'd just use the larger optics.

- The best focus that i can use for cut and engrave without change every time the lens?(or what is better focus lens?)

Use one of the nice adjustable heads from LightObject.

- Output nozzle hole diameter?

Not something you need to worry too much about. Bare minimum, the beam has to make it through. I'm running tests with a paper cone on my machine, and my test nozzle diameter is around 3/32".

- Distance between output nozzle tip and the workpiece?

I'm running my test nozzle at 1/8" above my workpiece. This is on acrylic, so I'm purposefully injecting air into the cut.

- o-rings need to be termal or the temperature of the optics is low?

No. O-rings can be normal black rubber. The optics should not be absorbing laser radiation, so should not heat up at all.

- what pressure of airflow is better?

The output from a small aquarium or airbrush compressor is sufficient. It is merely there to keep smoke from being deposited onto the lens and to help clear smoke from around the cutting area.

- the diameter of laser beam for a 40w 60w and 100w where i can find them(are the same for each manufactor?)? It depends on the distance from co2 laser nozzle?

If the manufacturer provides specifications, it'll be in there. If not, most beam diameters are in the range of the diameter of a pencil. Larger tubes will give a slightly larger beam. For larger machines, this becomes more of an issue to focus on. Also relevant would be the beam spread.

[Yaro]

Thank's for your answers.

I want ask you also if the mirror glass in the laser head, is in direct contact to aluminum or have a spacer or o-ring to reduce vibrations?

[TLHarrell]

Not an issue of vibration. Most mounts, the lens sits right against the metal and any o-rings are used for compression and spacing so you don't over tighten.