Cheap (Free?) Mirror Replacement for your CO2 Laser

hdd mirrors

You know what’s expensive? Those little tiny little mirrors used in laser cutters — and they don’t last forever either! What if we told you it’s possible to make your own for free, using a broken hard drive?

[Tim Wehr] read about using HDD platters as mirrors on BuildLog.net, and decided to try it out for himself to see how well they work. He quickly salvaged an old hard drive and removed the ever so shiny platters. Using a few pieces of wood he clamped the platter and then cut circles out of it using a metal hole saw — the edges are a bit rough, so we’d recommend you invest in a diamond hole saw if you’re planning on trying this.

Some denatured alcohol polishing later and a bit of filing on the edges, and he had a replacement mirror. He then performed two tests using both the original and the HDD mirror on his CO2 laser. Almost identical cutting power. In fact, [Tim] muses that the HDD mirror looks like it cut slightly better even! Not bad!

[Thanks Riva!]

Comments

  1. MrX says:

    I used to work in an optics research laboratory, it was a fairly common practice to use HDD plates as replacement first-surface mirrors.

  2. ejonesss says:

    why are the mirrors so much?

    it isnt like they are made of or coated with some kind of rare or restricted substance that requires a license or even haz mat license to handle and buy?

    • Jason says:

      The quality of the coating. A front-silvered mirror used in a lab setting usually has a surface flatness of lambda/10 (to preserve the quality of the wavefront) and a scratch-dig specification of 25-10 (to prevent scatter). So assuming a 10 micron wavelength for a CO2 laser, the variation between the high and low points on the surface of the mirror has to be less than 1 micron, and any scratches or scuffs on the surface must be less than 25 and 10 nm respectively.

      That’s just the glass that the mirror coat is deposited onto. Getting an acceptable, uniform coating as described above requires some serious hardware.

      • medix says:

        “Getting an acceptable, uniform coating as described above requires some serious hardware.”

        Yep. Usually a very large, walk-in high-vacuum chamber for sputter-coating as they’re often coated in batches. *really* awesome stuff if you ever have the chance to see it in person ;)

        • colecoman1982 says:

          And then don’t forget all the special packaging and handling required to ensure that those high tolerances are maintained from the point of finishing the glass’ surface to the point it’s delivered to the customer. Also, don’t forget to take into account the fact that lab grade optics are being produced for a vastly smaller market than hard drive platters. The significantly smaller economies of scale also probably play a big part in the price difference.

    • Adam says:

      And, conversely, why are HDD platters so cheap if they work (at least close to) as well?

  3. m4rkiz says:

    make sure that you check what is the platter made from before cutting ;) there is plenty of drives (mainly 2.5 inch) with glass\ceramic platters

    • medix says:

      Easy test: Accelerate (throw) drive towards (hard) floor then pick up after it stops bouncing. If the contents of the drive rattles, it is (was) ceramic. I don’t think I’ve ever encountered a dead drive of the 3.5″ variety that had ceramic platters however.

      • colecoman1982 says:

        It’s still made of glass/ceramic at that point, you’ve just multiplied the number of platter in the drive. If you can manage to throw a hard drive at the floor hard enough to convert the platters from glass/ceramic to another kind of matter then you have a very promising career waiting for you as a Major League Baseball pitcher…

    • barry99705 says:

      Like this one, who died from a head crash.

  4. Ren says:

    It’s a hack!
    B^)

  5. RexJaguarius says:

    Interestingly, I just read up on this process over the last few days as I have a ‘new’ eBay laser with a cracked mirror. I didn’t have a drill press handy, so instead I hand shaped a piece of copper PCB, polished it with 600, 800, 1000, 2000 sandpaper and then metal polish. It’s been working great for a week now, though it may not have the longevity of hard drive mirrors or silicon/gold.

  6. Oddly says:

    To prevent the edges from coming up, clamp the platter between something hard(like metal) and put your clamps as close to the hole you are going to drill as possible to make sure the metal pushes onto the platter. Also, put the good side of the platter up.

  7. Martin Raynsford says:

    I read this once before somewhere, Oh yeah it was on Hackaday, must be a slow week for hacks :P

    http://hackaday.com/2012/07/01/hackaday-links-june-1-2012/

  8. svofski says:

    Diamond saw/drill + aluminium platter sounds like a recipe for a sad evening, no?

  9. fartface says:

    Enjoy the shattering on the drives that have glass platters. Be incredibly careful and be sure you are using one with a metal platter.

  10. cplamb says:

    Couldn’t a glass based platter be cut with a diamond saw if it was done with water lubrication/cooling?

  11. Galane says:

    Glass or ceramic platters could be cut if you have access to an abrasive water jet machine.

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