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Old 08-13-2011, 01:48 AM   #1
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Exclamation Laser for hobby CNC-use?

Hi guys. I wasn't sure which subforum to post this in, but I guess here is best as it's modding and experimental. Although I ponder about red lasers now it wouldn't really belong in the red forum if someone suggests other colors so here goes...

I am after advice and guidance relating to lasers for neatly slicing through plastic film like the thick stuff used for transparrancies/overheads in laserprinters/copiers. I am trying to cut stencils for use in electronics soldering (solder stencils) and after trying drillbits and other milling as well as hot-needle type cutting (just gets full of gunk from cutting!) I ended up starting to look into lasers.

I've read up on protecting my eyes and such and have a few laserpointers up to the 50mW range already (and am very carefull about where and when I use em, mostly chasing seagulls off the lawn in the wee morning hours).

Putting my EE training and experience to good use I started by picking apart one of my derlilict dvd-rw drives (a SH-S223) where I quickly found a dual-diode assembly whithout the traditional slug, but instead a huge heatsinky thing with the red diode molded in together with it's IR brother using a common Cathode. I got it running with a simple linear regulator type constant-current drive and have tested it up to 227 mA so far.

By modifying the heatsink I managed to make it match the diode-slug from a 5mW red laser so I could reuse it's frame and twist-focus lense.
It's hard to focus when you avoid looking at the beam, reflections and spot but I managed to go by smoke on a non-reflective dark surface and have it fairly well focused at 3" with no noticeable burn-danger 1/2" infront and back of this point.
This is good for me as I intend to put it in my cnc machine where I only want to cut through the suspended film but not scribe patterns in the base table. (MDF burns!)

Attached are some images resulting from testing with sharpie-coloring the plastic sheets. It's mostly fast swipes and it's obvious that slower move can cut the plastic but it's not very clean. Images had to be rescaled to 800x600 so they have about 418 pixels/mm for scale. Film is only 0.1mm thick and it appears so is the focal point of my beam when approx ok focused. If I could cut with that accuracy I would be a very happy man. It would be accurate enough for my smallest details like the really small pads on some chips.

When it comes to the machine operating I will probably have to run slowly so best not to be in room while it works. It's too tempting to look at it.
I'd like a ref to a good place to buy some RED blocking shades/goggles but I am quite dissapointed in the OD 2+ stuff being sold all over. It seems I could get OD 4+ for same money, but I need to find somewhere that ships to Norway.
I'd also like tips on how good the goggles need to be vs the power of the laser even though I think I want 4+ regardless.

If anyone knows how far I can push the diode from that SH-S223 I'd be thankfull.

I have started with RED laser for a few reasons. It is my understanding that red lasers are direct-type laserdiodes and as such will have little stray frequencys. This should make it safer in regards to blink reflex and optics focusing what is really there and not focusing something else another place too. There may however be good reasons to use something else, so I am all ears...

As a final comment I will note that I won't post detailed images of modifications and such here as I don't want any kids starting to reproduce this from their old dvd burners. I have a certified lab to work in allowing me to do these mods without ruening the diodes and other parts but most kids won't. (Luckally...)
Attached Thumbnails
Laser for hobby CNC-use?-burn_170ma_3_670pix_pr_mm.jpg   Laser for hobby CNC-use?-burn_227ma_670pix_pr_mm_1.jpg   Laser for hobby CNC-use?-burn_227ma_670pix_pr_mm_2.jpg   Laser for hobby CNC-use?-burn_227ma_670pix_pr_mm_3.jpg  
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Old 08-14-2011, 09:13 PM   #2
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Default Re: Laser for hobby CNC-use?

Safety first: Don't use you laser if you don't have appropriate laser safety eyewear. With all your training and experience you should know this.

The stray frequencies you mention is probably the IR output of a green DPSS. Try getting a blue laser diode, much more power then a red at a reasonable price. Next stop would be a CO2 laser, but I suggest you get familiar with laser before getting to that.
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Old 08-14-2011, 09:22 PM   #3
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Default Re: Laser for hobby CNC-use?

If you want a good pair of goggles try OEM laser system. They are expensive, but well worth the price in my opinion.
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Old 08-14-2011, 11:16 PM   #4
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Default Re: Laser for hobby CNC-use?

Currently I have some cheap crap that is rated OD 2 and I think the films on em aren't even colored through, just coated. Thus I simply stay away from the beams alltogether.
I manage this by using the cnc to focus the beam by running testscans at a steadily increasing elevation (z) and then looking at result after laser is off again. Finding the best focus height and then deciding if I should adjust. Rinse and repeat.
I have it ok focused at 2.5" distance now and ran a test on some blackened sheets.
As for the powerlevels. All I need is something that can barely burn through a 0.1mm sheet of plastic. So far I am blackening it though.

Here's a video, with the laser controlled by the computer so I could leave the room and not be tempted to look.

http://www.youtube.com/watch?v=3U_rUmlGIvw

As for stray frequencys, yes green is bad with all the IR it generates. But I have seen shocking numbers on blue too. It seems there are 3 different types of blue diodes. Some produce ir.

I have these coming btw: Laser Glasses - Red laser beam protection 600-740nm :: Laser Safety :: Dragon Lasers
I chose them as I like red lasers with their relatively clean output.
They are rated OD 4+ at 190-450nm as well as for 621-740nm which should make em ok for blue/purple lasers as well as red right? Many appear to be 405nm others are 445nm. Both should fall within the 190-450 range although not by much in the latter case.

Last edited by KreAture; 08-14-2011 at 11:18 PM.
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Old 08-19-2011, 01:19 PM   #5
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Default Re: Laser for hobby CNC-use?

Will the glasses I have coming be ok for a 1w blue laser? For example one of those projector diodes. As people mention, the absorption of shorter wavelengths in plastics and such (that I will be cutting) is better than for red.
Still want to be safe though...
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Old 08-22-2011, 07:13 AM   #6
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Default Re: Laser for hobby CNC-use?

Yes, if they are indeed rated at OD4. I do wonder how long they'll last under direct exposure.

The best lasers for cutting plastics are CO2 lasers as plastics are opaque to the far infrared wavelength of the CO2 laser, and the CO2 lasers produce far higher wattage than diodes.
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Old 08-22-2011, 11:11 AM   #7
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Default Re: Laser for hobby CNC-use?

I think they won't be ok for brilliant blue, only purple-blue.
190-450nm doesn't cover the 457/473 nm range.
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Old 08-22-2011, 02:44 PM   #8
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Default Re: Laser for hobby CNC-use?

No blue direct diodes produce IR. The only diodes that produce IR are IR diodes and DPSS systems, but only because there is an IR diode pumping those.
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Old 08-22-2011, 03:16 PM   #9
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Default Re: Laser for hobby CNC-use?

Thanks Wolfman, then as long as I stay away from 457/473 I'll be fine. Or atleast as safe as glasses can make me. The rest is still up to me.
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Old 08-22-2011, 03:35 PM   #10
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Default Re: Laser for hobby CNC-use?

Quote:
Originally Posted by BittyNittyMitty View Post
I know NOTHING about lasers, could I import a Wicked Laser
Core 5mW into Australia?
Would it get through customs?

Btw I live in Perth

Pls reply
What does that have to do with this Thread...
Try to read the Thread Title Subject before posting...
It will save you a lot of grief.....

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Old 08-26-2011, 02:51 PM   #11
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Default Re: Laser for hobby CNC-use?

Is there any practical and cheap way to get around 1-2w with a good cooling-setup now?
I think that will be fine for my needs, and I see CO2 lasers start at around 20w.
Also I really distrust invisible beams...
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Old 08-26-2011, 02:55 PM   #12
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Default Re: Laser for hobby CNC-use?

Easily. Use a 445nm diode. Those reach upwards of 2W in handheld systems (but don't expect to get any more than that even with crazy cooling).
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Old 08-26-2011, 03:07 PM   #13
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Default Re: Laser for hobby CNC-use?

I am almost done with my new TEC regulator. It will control a TEC relative to ambient allowing me to set a certain deltaT or absolute allowing for a specific C.
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Old 08-26-2011, 03:17 PM   #14
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Default Re: Laser for hobby CNC-use?

That's neat. How did you go about doing that?
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Old 08-26-2011, 03:47 PM   #15
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Default Re: Laser for hobby CNC-use?

The preliminary circuit is here:
http://kreature.org/projects/laser/tec-reg_v0.4_sch.png

And layout here:
http://kreature.org/projects/laser/tec-reg_v0.4_pcb.png

I wanted to etch a board myself so I tried getting it 1-sided.
I did flow backside so I can optionally link it in if the groundplane is too poor.

Basically it's a ATtiny10 microcontroller that reads two NTC resistors and calculates temps. One is for air-ref and other is for cold-side. By utilizing the reset-pin from 5v down to 2v(ish) I can also have a potmeter input for setting the temp. By disconnecting the air-ref I can detect it's missing and go for a absolute ref instead allowing both solutions to be integrated without more pins.

The FET is capable of 17 amps so there shouldn't be many issues with 0-6 amps TEC which I plan on using. As long as the coil can take it, it should work ok.
The optocoupler is ok from 10-30v but bootstrap makes max around 15v so better stick to 12v.
The opto is a push-pull style and I use a bootstrap to allow a highside n-fet. The Vgs of the FET is however only 20v so I think I should change the bootstrap to work from 5v not input. I only need 2-4v abowe input for proper operation anyways.
Pwm will be 31 kHz at 8-bit, but I may drop it to 6 bit for 125 kHz.

Last edited by KreAture; 08-26-2011 at 03:52 PM. Reason: Corrected data.
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Old 08-26-2011, 04:39 PM   #16
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Default Re: Laser for hobby CNC-use?

I don't understand - why use an opto-coupler? Why not just use a rectifier diode so current only flows in that direction?

Still need to do more work with uCs

EDIT: And where do you get the pin-headers and their equivalent female components?! I can never find them!

Last edited by Wolfman29; 08-26-2011 at 05:45 PM.
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