Re: Laser Engraving

Hi Whelen,

Last year I was looking to purchase a laser engraver.
Here is what I learned, take it for what it's worth.

Of the three big boys (Epilog, Universal, GPC) they use sealed (gas) CO2
laser tubes. Sealed CO2 tubes have a shelflife of about 3 to 4 years, even if
in use or still in the box. After that, their power output decreases
(basically).

Most of the mfg's can recharge and replace the mirrors in the tubes.

The older type of CO2 laser tubes are flowing (as opposed to sealed), where
you have the welding supply mix you up a special receipe of gases and you
just refill the tank when it gets low.

CO2 lasers can NOT mark/etch/cut metals. The wavelength is wrong.
You'll need a YaG laser for true metal work.

The metal marking stuff is just like pottery glaze.
You brush it on the metal, the laser "cures" it, and you wash away the rest
with water. It does not mark the metal in any way.

Now, if you have anodized metal, a CO2 laser can "bleach" the anodize itself
(usually comes out a off cream color). It doesn't matter what color the
original anodize is (red, blue, gold, etc) the bleaching will always be the
same off cream color.

You can even bleach the color out of denim to produce patterns in fabric.
(I was told this process of bleaching fabric it patented, so...)


All of the laser use flying optics (moving mirrors to position the beam).
The laser *MUST* be focused to the top surface of the material before each
run. If not you will get a gooey blob (in the cast of plastic), so altering
the Z height itn't going to do it.

A 35 Watt CO2 laser can cut 0.25" thick wood. But if the wood is dense it
might be better to make two passes instead of one big one to get a nicer
finish. I took a scrap piece of teak wood and had they cut it for me. Not a
pretty sight on such a low power laser. Too slow feed and low powered cause
the sap to melt/burn and char the edges.

The power levels (like depth) is controlled by pulsing the laser (plus
something else I can't recall at the moment).

They all use HPGL (plotter) and not G-Code for controlling movement/power.

Also most all of them are installed like a printer and most everyone in the
engraving industry uses Corel Draw.

I started to ask around about used lasers and found someone that engraves urn
boxes (beautiful work) professionally. He was selling a 75 Watt C02 laser
engraver because it was too low power to engrave on the surface of softwood
0.125" thick in a reasonable amount of time.

I hope I didn't ramble too much and the information was helpful.

Jim...

> Date: Mon, 07 Nov 2005 18:45:57 -0000
> From: "whelenremington" <wperun1@...>
> Subject: Re: Laser Engraving
>
> Bob, thanks for your reply. As you know I e-mailed you for
> information on pricing. It may be useful for the rest of the group
> to repeat some of my questions. I can see how conventional CNC mills
> will move the x and y axis so that the laser can "cut" the design.
> You can see what I mean by design on the web site - (
> www.epiloglaser.com/applications.htm ). But, what varies the
> intensity of the laser to "change the contrast" of the design
> being "cut" by the laser. I am using the software Virtual Sculptor
> 3D, ( www.designscomputed.com/vs3d/ ) . VS3D is both CAD and CAM
> software, and works in both raster and vector space. So it generares
> the G-code for the Z-axis heights as a function of image contrast.
> Now my question is - do I let the Z axis move the laser to achieve
> the "intensity levels" to achieve the contrasts in the image, - OR do
> I need electronics to read only the Z axis G-code from VS-3D and use
> the electronics to vary the intensity of the laser?
>
> Will a low power CO2 laser yield a "material burn" proportional to Z
> axis movement? Does anyone have an idea of how Epilog Laser does
> this in their machines? Are there various ways to do it?
>
> Thanks for your help.
>
> Whelen

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