Focal length and laser power for engraving

Hello,
i'm building a laser engraver, using a 150mW red diode.
The laser it is mount on an AixiZ 5.6mm housing.

I'm wondering this: does a 5 to 30cm distance from the laser to the engraving working plane affects the engraving capabilities of that laser?
In other words, fiven a 150mW power laser, if i place the laser 5cm from the object i would like to engrave, or i place it at 30cm, and of course i adjust the focal of the laser, does it get !substantial! change of cutting capabilities?

thank you for helps!

It probably depends how it spreads out. I don't know. Anyways I'd use more power.

It's a junked-DVD led, so that's more or less the power.

hozone said:

I'm wondering this: does a 5 to 30cm distance from the laser to the engraving working plane affects the engraving capabilities of that laser?
In other words, fiven a 150mW power laser, if i place the laser 5cm from the object i would like to engrave, or i place it at 30cm, and of course i adjust the focal of the laser, does it get !substantial! change of cutting capabilities?

Click to expand...

Let's assume that your laser power is enough to cut whatever you want to cut,
then closer you focus a smaller spot you get, and a higher intensity to heat your material. There could be a tradeoff for the quality of the spot as a lens probably is designed for collimation.

Focal distance doesn't matter as much if
you are only engraving, not cutting. For
cutting, you want it focused out farther to
give better depth of focus. Focusing
farther out also puts the lens closer to
the diode and reduces clipping if there is
any. Probably the only time you would want
to focus closer in is if your CNC is so
short that it becomes necessary. If your
diode can engrave well, then I would
suspect that it was a bit more than 150mW.
You should also have a fan running to blow
the smoke away from the optics.

Thank you for help and for interesting replyes.
Yes i will add a fan, as i've already done with the other smaller engraver i've built.
I suppose it's 150mW, but i'm not sure about that, what i'm sure is that it is a red dvd-writer diode.
I will write here for further news in this project.
Just to let you know, I was using a ebay cheap driver, now i'm testing this driver:
http://laserpointerforums.com/f51/simple-linear-mosfet-dimming-circuit-pwm-70812.html