Cover Window Material

Issues related to safety

Cover Window Material

Postby lazerous » Mon Nov 23, 2009 11:57 pm

What is a good material for the window on the cover. I have found some sources, but they are extremely expensive.
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Re: Cover Window Material

Postby bdring » Tue Nov 24, 2009 12:46 am

I have not actually built my door/cover yet, but...

I did some research on this and found that very few materials are transparent to the 10.6um wavelength of CO2 lasers. I found this document (http://www.synrad.com/LaserFacts/laser%20safety%20requirements.pdf) document at Synrad that agrees with that. I added some info to my research section (http://www.buildlog.net/cnc_laser/cnc_build_research.htm#SafetyWindow).

Since I did that research I have been cutting and engraving a lot of materials. You can engrave all day on a piece glass, acrylic or polycarbonate and no real energy appears to go through. As an experiment I put a piece of glass on top of a white piece of paper and engraved very stongly until I enventually shattered the glass. No discoloration appeared on the paper.

With that said, I now realize the invisible IR is only half the story. When cutting or engraving most materials, the point where the laser strikes the material is an intense white light, like the tip of a welding torch. This must be burning the material and gases. It hurts your eyes to look at it even through IR laser safe glasses. Therefore, you really want something to shield both the primary IR light as well as the intense visible light.

This may be why some lasers have tinted covers. I am almost temped to buy some flip up retro looking welding googles.
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Re: Cover Window Material

Postby LeonS » Wed Nov 25, 2009 8:19 pm

I saw on another site that regular clear Plexiglas will work just fine. It absorbs IR but it will not burn thorough unless it is sharply focused. The cover in the worst case will be receiving reflected IR from shiny target materials or from the hardware due to mirror misalignment or severe vibrations. In either case the IR radiation would be defuse and not damage the cover. It seems you want the window to absorb the IR, right?

Cheers!
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Re: Cover Window Material

Postby LeonS » Wed Nov 25, 2009 8:21 pm

Some steam punk retro goggles would not only protect your eyes, but you would feel wicked cool.
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Re: Cover Window Material

Postby bdring » Thu Nov 26, 2009 2:21 pm

Yes plexiglas should work fine for IR safety. I don't know what to do about the brightness factor. Regular sunglasses don't help much, so I doubt tinted plexi will help much.

Yes the steampunky goggles are cool, especially when you see how dorky most IR safety glasses look.
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Re: Cover Window Material

Postby lasersafe1 » Fri Nov 27, 2009 8:58 pm

First Statement: Everything I'm about to say is wrong from a safety standpoint.
Second Statement: These statements only apply to your laser engraver that has the focusing lens in place.

1. 10.6um from the CO2 is absorbed by water, glass, plexiglass, lexan, etc.
2. I bought a cheap 40W laser engraver from ebay and I routinely operate it with the cover lifted.
3. I always make sure I'm wearing my glasses. Plain old reading glasses.
4. The beam is always directed down toward the workpiece.
5. The lens focuses it to a pinpoint about 2" below the lens. It is highly divergent after that point, so if it reflects up from the workpiece it will diverge quickly.
6. I have done some tests in the past where it indeed reflected up toward my face. I could feel the heat from the laser as it hit my face. It was sort of like a heatlamp over my whole face.
7. I was glad I was wearing my glasses, but even if I hadn't had the glasses the laser light would be absorbed by the water on the surface of the cornea. This is bad, but not nearly as bad as a laser of visible wavelength that will travel through the eye and focus on the retina. Retinal damage is usually permanent. Cornea damage can be permanent or non-permanent. The cornea can be sugically replaced.

I don't have the necessary equipment to actually measure the neutral density attenuation of my glasses, but I would be willing to bet that they meet the ND level required to keep the laser attenuated below the MPE (maximum permissible exposure) level for 10.6um specular reflections as long as the laser focusing lens is kept in place. If you remove the lens and hit a reflective object, the collimated beam may be directed toward your eye. Even the commercial laser safety eyewear would not protect against this.
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Re: Cover Window Material

Postby bdring » Fri Nov 27, 2009 9:19 pm

Do you have issues with the brightness of the visible light of the "burn"? Mine is freakishly bright sometimes and you will see spots for a while after looking at it.

I am tempted to mount a little piece of a welding lens on the X-axis where you could look through it. It would move with the cut. If it were positioned right, you could easily look around it too.

I was at a sheet metal fabricator the other day where he was using a 2500W CO2 laser on steel. There was very little protection. You could see the contact point sometimes.
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Re: Cover Window Material

Postby lasersafe1 » Sat Nov 28, 2009 4:16 pm

When something is too bright to look at I simply look away. The bright glow produced by something burning is in no way a coherent form of laser light. Yes, you can get flash burns on your retina from this, but it is usually not permanent. I agree that if you really need to look in order to make an adjustment to the cut, then welding goggles would be appropriate.
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Safety Filter

Postby cozmicray » Sun Dec 01, 2013 11:39 pm

I am looking for cheap material to make safety window for
445nm (blue) 1.75W solid state laser.

Real bright looking at reflection off any material being engraved or cut
and
I don't want to be using a white cane after a laser session.

Know of any suppliers of plastic to make safety windows?

:o
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Re: Cover Window Material

Postby cvoinescu » Mon Dec 02, 2013 12:21 pm

For that wavelength, I would use Dibond for the window. :) Actually, I'm way too chicken (and treasure my eyes too much) to even consider using that type of laser, regardless of enclosure.
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