Newbie- Laser Strength

[RiseUp]

My little brother loves my CNC router(he helped me build it), and has recently discovered the online tutorials on how to make your own "laser cutter" from a dvd burner diode. He came to me for help, as he wants to build a small (14"x14") laser cutter, using that diode. I figure it's roughly 200mw at the MAX, so it's okay for cutting stencils from thin paper, but otherwise useless.
He's adamant about funding this entire project, so he started looking for cheap laser diodes, and found a few 1 watt diodes on eBay for about $10-20.
What could he cut with one of those?
There's also a 4 watt for $30, and a 12 watt coherent diode for $40.
Could he even use a coherent diode, or are the optics too complex for a desktop machine?
I'm new to laser cutting, so please excuse my limited knowledge.
(His budget is roughly $150, but he's down to about $50 after the last trip to Home Depot. I'll probably end up buying the diode for him as a gift though.)

[zax15uk]

The DVD diodes are easiest, since you can just install them into a standard (meaning cheap) housing which has the focus lens. Power supply requirements are also lower so cheaper too. The downside is as you said, the cutting power is very low so not much use but they can be used for engraving on wood etc.

You could use a 1W diode, but make sure to price up the power supply and required lens before jumping in.

Zax.

[RiseUp]

I'll probably end up buying whatever he ends up needing, if I don't have a few power supplies laying around as it is. What about strength though? What materials/thicknesses can he expect to handle with something <10 watts?
I was thinking he could cut 1mm balsa MAYBE, on the maximum end, and at least strong enough to engrave it. Am I wrong?

[zax15uk]

There is more to the equation than 'power', especially with diodes that are often rated at input current. So a 10W @ 50% efficiency is 5W of light energy output, substract the losses for lens and air from that too.

The wavelength is also important, different materials absorb or reflect different wavelenghs.

What is most important though is the power density. A 1W laser focused to a few micron spot size (expensive optics) would have greater cutting power than an unfocused 100W CO2 laser.

So, back to your question. Yes, a 10W diode laser with glass optics would be able to cut 1mm balsa and Acrylic. It would also be able to engrave on wood and other materials. Just stay away from any linear/bar IR diodes, these require very expensive optics to collimate into a usable beam.

Zax.

[RiseUp]

Looking at other examples, a convex and concave lens is used, and placed in a screw type housing to adjust distance between lenses. A basic collimator, I believe.
From what I've read, a simple magnifying glass would work, but I'd much rather use optics made specifically to do what he's trying to accomplish. Any links to useful optics suppliers(who don't require orders of >100)?
I apologize if this seems like another obnoxious "newbie demanding answers without searching for them because he isn't the first to ask", but I've Googled and forum-searched many times before resorting to bothering you guys with irritatingly simple (to you) questions.
I know I'm basically having a conversation with myself on this one, but if he were to properly focus the 1w laser diodes beam,using a simple DIY collimator, could he expect to at least cut 3mm Depron foam(used for RC planes,helicopters,etc)?
Video of laser collimation process

[RiseUp]

I found a biconvex lens at surplusshed.com. 10mm dia, 26mm FL, uncoated for $4. If I used this, would the fact that its diameter is larger than my laser diode interfere with its performance? ie, Laser diode=7mm. Lens=10mm. Problem?

[zax15uk]

No, the lens diameter doesn't matter.

A 1W diode and standard optics would probably not cut the 3mm depron, or at least not at any reasonable speed. It would likely melt it's way through slowly and not produce a good cut.

Zax.

[RiseUp]

Okay.
I'll probably make him do the extra homework on what WILL work(and how much it'll cost) for a simple machine. He'll probably cut thin foam and engrave/etch acrylic. I'm guessing somewhere around at least 10w.
Thank you Zax.
RiseUp

[zax15uk]

A 10W system (CO2 or high IR diode) would be ideal, and 5W sufficient if correctly focused.

If you buy surplus I would expect $100-$200 for the diode laser, PSU and optics. Probably $200-$300 for a small CO2 tube system.

Here are some ebay examples (I do not have any affiliation or experience with them - so this is not a recommendation just somewhere to start):

http://cgi.ebay.com/HIGH-POWER-5W-CO...item439ae26c8e

http://cgi.ebay.com/HIGH-POWER-IR-91...item4ceb914948

Zax.

[RiseUp]

Wow, thank you Zax. I was somewhat aware of the price range. Those seem to be decent enough lol. The Synrad CO2 tube comes with its own driver,too. 1 day left, 5 bids already,man I hope I can pull the old 'wait and pounce' technique by bidding on it in the last 5 minutes.
I appreciate the info. If he ever gets this thing up and running (or even buys the laser for that matter) I'll definitely post a build log for such a tiny lasercutter.
RiseUp

[zax15uk]

Those surplus 5W Synrad lasers were being sold over at LPF for $150 shipped.

http://laserpointerforums.com/f39/5w...red-23204.html

The surplus Synrad RF tubes are generally a good buy, but this is an older version and not their new metal resonator but still worth considering if the price is right.

Zax.