How does it work?

[David Fried]

Venturing into the laser forum ... scary.

I was just looking at Pete Simmons post, "My best yet" and I realized I don't know why the laser engraving works. OK, I assume the laser removes (vaporizes) some material. Is it changing the surface angle or texture (therefore reflectivity) or what? Looking at the engraving on Black marble it looks like a gray scale image. How many different levels can you create in an image? How much is a question of the laser and how much is due to the material?

Simple lettering never made me think about it but those photographic images have get me wondering.

I'll bet lots of creekers don't know why the laser stuff works and how you folks can do the things you do. Could someone explain it please. Thanks.

[Jerry Allen]

The quick answer:
In blasting of the shiny black surface, it leaves a white dot (pit). Analogous to using an inkjet or laser printer. To get the shades of gray, as you would have to do on any bitmap machine, you convert the photo to black and white dots (how many and why according to content and medium) and in this case invert them (black is blast). The machines are also capable of vector lines for cutting or just continuous poit to point lines and curves. Doing text is bitmap but does not require a screen or dot placement algorithm as a photo does.

[Kevin Huffman]

Hello David,

Yes, the laser is a very powerful beam of light. It is generated by the laser tube and then bounced through a series of mirrors and directed to the head. In the head there is a lens. The lens refocus's the laser and concentrates it into a certian area where it actually do some engraving. Kind of the same thing as when you were younger and used to burn ants with a magnifiying glass. You had to move the magnifying glass back and forth until it focused and hot enough to set ants on fire. Basically the same principle just a lot hotter.

The concentrated light actually takes away particals and/or burns the material. In the case of marble, it is taking material away exposing the color underneith it, white.

There are a ton of grays that can be had. Your software and laser just have to be able to lay down different patterns of dots, which will allow different amounts of white to show through. Which gives you the different grays.

Alot of engraving has to do with the material. Some materals like marble start black and engrave white. Most other materials are lighter and engrave darker. Laserable plastics are two different colored plastics melted togheter, you engrave the top color to show the bottom color.

Photographs are pretty easy when you thing about it in greyscale (black on one end of the scale, white on the other and all the grey's in between). The laser driver always changes an image to greyscale before it sends it to the laser. Grey is always a % of black and a % of white. White is always 0 speed and 0 power. When the laser comes a across a grey it looks at its chemical make up. Lets say this grey is 65% black and 35% white, the laser will adjust the power of black and only use 65% of the power of black on this gray spot. The speed will remain the same. When it come to another grey it looks at it and adjusts the power for the % of black it has it in. The darker the grey the deeper the engraving because the laser uses more power, and vice versa. The lighter the gray the lighter the engraving because the laser uses less power.

I hope this makes a little bit of since. I know I am rambling. If not just reply and I will try to explain better.

[Rodne Gold]

Doesnt the laser only vary the power when it does 3D?
Photos are all lasered at the same power with diff dot spacing AFAIK.

[Nick Adams]

I would assume, by nature that a greyscale image is nothing more then a solid line that varys from white, to black, and vice vs.

However a true bitmap image would only be that. A series of dots, spacing and grouping to give shading and depth.

However, I do not fully understand the drivers total functionality as far as processing images sent to the laser. So I would, and very well might be way off.

[Rodne Gold]

Nick
You cant achieve lighter or darker engraving by varying power on most substrates , all it will do is engrave deeper. For example a laminate with a white cap and and black substrate will either engrave white (the cap isnt fully removed) or black (the laser vaporises the cap) , nothing inbetween. If you were using that to reproduce a photo , varying power is useless , what you have to do is find a power setting that vaporises the cap and use a halftone image to represent the photo.

[Nick Adams]

I understand that. I guess I was thinking of wood more so, since I work with it daily.

On another note, my legend 75watt 32ex is working wonderfully.