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Laser protective acrylic

Discussion in 'Laser Cutters' started by nportelli, Mar 28, 2018.

  1. nportelli

    nportelli Well-Known
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    What do people use? And why is it so expensive? Is it because it is tested or special type? I'm looking for a protective sheet for a 445nm diode laser.
     
  2. BNMaker

    BNMaker Veteran
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    For a 445nm laser, orange acrylic in 3mm will give you ‘adequate’ protection from the odd stray reflection for diodes <3W, but there’s no substitute for glasses and you should still wear them - you’ve only got one spare eye ;)

    The darker the orange tint, the more the protection.

    You can beef up the protection if you have a 3W<8W laser by putting a layer of reflective acrylic ‘one way’ sheet on the inside. The kind of stick-on sheet you would use for an infinity mirror (which is where I got mine - off-cuts from my infinity clock).
     
  3. Giarc

    Giarc Master
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    I bought a piece from jtech photonics because even with glasses, I did not feel the protection was adequate because reflected light would get under the lenses sometimes. The stuff they sell is tested. The shipping is what was expensive, but it came in two days. I looked at Tap plastic's orange acrylic but no data was available so I went with jtech. I need my eyes to make a living - and because I like them. It was worth the $32 IMHO.
     
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  4. Scotty Orr

    Scotty Orr Master
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  5. Giarc

    Giarc Master
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    I am building a box as well. Unfortunately, mine will be much longer since the focal length of my laser is about 180 mm.
     
  6. JustinTime

    JustinTime Master
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    Scotty, is that a cream-cheese/sour-cream tub that is encasing your diode?
     
  7. Scotty Orr

    Scotty Orr Master
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    No, that's my 3D printed router adapter for my Makita - I just leave it in place when swapping out the router for the laser mount.

    20171211_155759.jpg
    20171229_133909.jpg
     
  8. Mark Carew

    Mark Carew OpenBuilds Team
    Staff Member Moderator Resident Builder Project Maker Builder

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    Scotty Orr likes this.
  9. BNMaker

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    Yep, you've only got one spare!

    But... orange is orange. These 'laser safety' companies are charging huge money for what is just normal coloured acrylic. They give all sorts of fancy figures, and 'OD' numbers, but what they really do is to buy a bunch of off-the-shelf acrylic and put it through a spectrum analyser - which you can do at home, except the cost of an analyser is more than a sheet of 'laser' acrylic.., but, I just happen to have a transmissive and reflective spectrum analyser and the absorption capabilities of yellow through red acrylic give varying levels of absorption of 445nm light, from over 50% to over 90%.

    And I live in the middle of nowhere in SE Asia, where you can't easily buy 'laser safe acrylic'... unless you want to pay US$150 for shipping of a 12"x12" square.

    There's nothing special about 'laser safe' acrylic - its just coloured acrylic that naturally absorbs a specific range of frequencies of light. Orange is high up on the visible spectrum - around 640-650nm - which means it doesn't transmit other, lower colours, but passes the range we see as orange.

    If you had a blue sheet of acrylic, that's low on the spectrum - 420-470nm, depending on the colour. That would pass a 445nm laser, but block a red diode laser at 640nm

    It very much matters a) what kind of laser - diode vs CO2 b) the power of your laser c) IR or visible spectrum d) the opacity of your acrylic.

    For IR lasers, even a sheet of clear acrylic will block 95% of IR. But a clear sheet won't do much at all for a visible-light diode... and theres a reason black acrylic is easy to cut - it absorbs all the energy and converts it to heat.

    So, don't worry too much about it - if you have a 500mw - 10W 'blue' laser diode, a sheet of 50% orange acrylic will cut down the transmission of harmful rays to a non-harmful level. So will dark sunglasses, but without knowing the colour of the glasses and the frequency of the laser, you are just being stupid to use sunglasses as your primary defence.

    And you can test it yourself - get a piece of acrylic you want to test, set your laser at 90deg to the beam, place a piece of tissue paper or other easily burned object and fire up. You won't even be able to scorch light tissue with the beam focused on the paper.

    Reflection is the major source of stray coherent light beams in unexpected places. And, unless you're cutting or engraving mirrors 0.o then the reflected beam is going to be significantly lower powered than the beam that struck the object. it will also absorb some of the 'speed' of the beam, shifting it to a lower frequency.

    If you want to DIY your laser shielding, get some complementary coloured acrylic and for additional safety some 'one way' reflective film for the inside and you will be fine - but ALWAYS wear your safety specs, even if you have shielding. One accident is all it takes.
     
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  10. Giarc

    Giarc Master
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    I agree with what you are saying. However, for me the decision was that since Tap Plastics was just a few dollars less for orange acrylic shipped to my house then Jtech was, and Jtech took the time to provide me with data I would go with theirs. I could have got the Tap Plastics piece significantly cheaper if I drove to the store, but I started putting a dollar amount on my weekend time and to me it was not worth the gas burned and the hour to hour and a half round trip.
     
  11. BNMaker

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    J tech haven”t made some special plastic - they’ve just sourced good quality orange acrylic.

    Most of the world isn’t within easy driving distance, and the original question was about what works.

    If it is orange, it’s filtering blue light.

    It’s not rocket science.
     

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