Making laser mirrors

[Richard Rumancik]

I had one mirror that was going bad so I purchased a replacement on eBay some time ago, just never got around to mounting it. I had to make a backer plate for it and just used cyanoacrylate to bond the mirror to the steel plate.

While I was at it, I recalled a post from last year from Chris DeGerolamo
http://www.sawmillcreek.org/showthread.php?188697-Making-Mirrors-From-Scrap-HDs&highlight=making+mirrors+from+scrap+HDs

where he provided a link regarding making mirrors from old hard disk platters. The method in the instruction was to use a hole cutter to cut round "mirrors" from the platter. For my GCC machine I realized there wasn't any good reason to make the mirrors round, so I just masked a disk and cut a rectangle on a shear. (I don't know if other manufacturers require the mirror to be round.)

Anyway the cutting stresses did distort the reflected image about 2-3 mm all around the rectangle, but the incident beam would not have been in that area anyway so it was not a concern. I did a quick raster test and it looked fine. I had just finished cutting 6 mm acrylic, so I used the same settings and I was able to cut through the 6 mm fine with the aluminum mirror in place.

This is not a quantitative test by any means but it does seem like a viable way to make a mirror, at least on an emergency basis. I think it is a lot easier to cut rectangles or squares than try to make disks.

I have no idea of the reflectance of a HD mirror as opposed to a gold mirror - if you used these for all 4 locations there would probably be a performance hit. I'd be curious to know what it is, but it would take a power meter to get any quantitative data and I don't have one.

[Dan Hintz]

At our power levels, the difference will not be measurable... enjoy the speed at which you could replace a mirror compared to shipping and keep lasering.

[Richard Rumancik]

With one mirror maybe there is no obvious difference - but what I was thinking was that if it is 95% as reflective as gold and I install 4 of them - then .95*.95*.95*.95 = .81 or 81%. Now that would be a big hit. But if it is 99% as good as gold, then no big deal. But I don't know which it is . . . in any case it is worth a try to get a laser going again.

(Maybe someone with a power meter and some free time will take the challenge to do some measurements.)

[walter hofmann]

Hi there
I am the guy who has invented this and posted this last year and many have allready used it too. I dont have a power meter but compared this with the gold mirrors the practical way side by side and there is no practical difference not with cutting and not with engraving.
A buddy of mine in germany who works for aerospace in R&D made some measurments of reflectivity and did find that the most of this round cut mirrors have a reflectivity of 99.5%. another importand part is that this mirrors are pretty scratch resistend what is very importand because they can be wiped of with lens cleaner and a lens wipe without scratches. I use them since 9 month and so many times cleaned no scratches. with the gold mirror they have scratches after a few cleaning pretty easly.
greetings
waltfl

[Richard Rumancik]

Walter, I did not realize it was your idea or I would have mentioned your name - my apologies. The trail was a bit long to follow as Chris linked to a site which reported on a post on another site . . . anyway thanks for sharing the idea with the community.

[walter hofmann]

Hi
no probleme no apology needed I am glad that so many followed it and safed some money.
greetings
waltfl

[Dan Hintz]

I am the guy who has invented this and posted this last year and many have allready used it too.

Sorry, Walter, but Instructables beat you to this ;) Here's an article from four years ago:
http://www.instructables.com/id/Make-a-laser-show-with-an-old-hard-drive/

[Martin Boekers]

In reading this I have a question? It seems this is a cheap solution for mirrors, how come someone hasn't manufactered these as it has to be cheaper than the front surface "gold" ones we buy. It seems this could be sold as a kit with 4 for the cost of one or two.
One more question are there any laser companies using this style mirror instead of the "gold" ones? It seem as this is right up the Chinese alley if it works as good or almost as good as the "gold" ones...

[Dan Hintz]

Martin,

Plenty of mirror options other than gold... this is just a convenient way to get back into business same-day rather than wait for shipping. It's an aluminum disk with polished carbon. Nothing special, but also not designed from the beginning to be a good front-surface mirror. It works, but there are better options for cheaper.

[Joe Hillmann]

Martin,

I don't think gold has much to do with the price of mirrors. The mirrors are gold plated so there is only a couple dollars with of gold in each one. Most of the expense I would assume comes from grinding an optical surface onto it and the economies of scale. The laser companies may make a 10,000 or so mirrors a year, the computer companies making the hard drives probably make that many in a day. And as is the case with everything the more specialized something is the more it costs.

[Matthew Grant]

Boy was I excited to find this old thread, but unfortunately it didn't work well for me.

I cnc'd three mirrors from an old WD IDE hard drive and slapped them in. The losses were about 8W per mirror, I'd call these particular mirrors about 85% reflectance.

It might vary by manufacturer or model, so scratch Western Digital Caviar off the list.

[Dave Sheldrake]

I'm testing some new mirrors from a UK based PVD company, double sided and have 99.7% reflective indexes.

Ok nothing special until you hear they cost $6 a pop for 25mm and $4 a pop for 20mm. Hit them with 230 watts so far and as yet no problems.

[John Noell]

Some of us would love to buy some (if they keep working for you). :)

[Kev Williams]

I made a couple of HD mirrors once. The one I installed worked great!


--for about 20 minutes... burned a hole thru it--

http://www.engraver1.com/erase2/mirror2.JPG


ooops, wrong kinda hard drive platter! Yes, I machined a plated glass HD platter...

ANYWAY, the reason I made it was the mirror over the lens had some pretty good scratches after 10 years. Of course, it went back in shortly after my failed experiment.

Then a few months later, my Gravo rep stopped by, and gave me a new mirror for helping him out on a job. The original mirror was silver, the new one is gold....

Switching gears a bit, I bought 3 laser pointers about 2 years ago, one red, one green, and one blue. I was experimenting with aiming them thru the lens on the Triumph. Once I got to the blue laser, I found that the yellow lens completely filtered out the blue laser light, 100%. I suppose then, that our lenses are yellow on purpose TO filter out blue light- so now I have 2 questions:

1- Why filter out blue light, and
2- Do the gold mirrors also filter out (not reflect) blue light?

I ask because, after just this mirror change on my 40w LS900, the usable power noticeably increased! And this power increase has made in necessary to change saved power settings going back to day one. Such as cutting tape, I've used tape settings for years that will cut thru the tape, but not the slick paper I stick the tape to. After the new mirror, I had to decrease the power and increase speed to keep from cutting clear thru the paper. So at 11 years old, I can honestly say this laser is working better than when it was new. (knock on my head!)

So naturally I'm curious as why the gold mirror would increase my spot beam power? Has anyone else had a similar experience?

Other than one X belt so far, this mirror is the only maintenance item I've ever changed out....

[Dan Hintz]

Switching gears a bit, I bought 3 laser pointers about 2 years ago, one red, one green, and one blue. I was experimenting with aiming them thru the lens on the Triumph. Once I got to the blue laser, I found that the yellow lens completely filtered out the blue laser light, 100%. I suppose then, that our lenses are yellow on purpose TO filter out blue light- so now I have 2 questions:

1- Why filter out blue light, and
2- Do the gold mirrors also filter out (not reflect) blue light?

So naturally I'm curious as why the gold mirror would increase my spot beam power? Has anyone else had a similar experience?

Our lenses are yellow because the material they're made out of, Zinc Selenide, is yellow... filtering out blue light (which doesn't exist in a far-IR CO2 output beam) is irrelevant.

Gold mirrors are high-efficiency reflectors of far-IR wavelengths, so that's why they're used.