2012-01-22

Get Your CO2 Laser Mirrors for FREE

Anyone who has been using a co2 laser for any period of time knows very well the two truths about the mirrors that direct the laser beam from the laser tube to the material being lazed:
  1. Mirrors will get damaged, needing to be replaced, and 
  2. Replacing the mirrors is expensive. 
The first one is inescapable, but maybe there is something you can do about the second. Follow along here and discover how to Get Your CO2 Laser Mirrors for FREE!

I have to start off giving credit where it is due. On one of my favorite sites, BuildLog.net, a poster, Walt A542002,  talked about making an emergency replacement mirror out of a hard drive disk. The idea intrigued me and I decided to put the idea to the test. The results were so impressive that I wanted to share with all of you the step-by-step procedure, along with a lot of pictures. So here it is, the step-by-step guide to making laser mirrors from a hard drive disk.


Materials needed:

  • Hard Drive
  • #9 Torx bit
  • Large straight bit screwdriver
  • 7/8" Metal cutting hole saw 
  • Flat file
  • Drill Press (or electric hand drill)
  • Masking Tape
  • A couple of scrap 1x6 boards
  • Denatured alcohol
  • Cotton swabs
  • 2mm Craft foam (optional if needed)

If you already have those on hand, you have everything you need to make 9 or more mirrors at zero cost.

(As you read, I highly recommend that you click on the individual pictures to enlarge them to see the detail.)

Let's start with the hard drive. If you have been around computers very long, chances are you already have a dead HD lying around someplace. If you don't, try talking to a local computer repair shop. They will certainly have plenty around and will likely give you one or more. It actually costs them to dispose of them, so giving some away is actually a saving to them.

The first step is to remove the 6 (or whatever is correct for your HD) screws around the perimeter of the drive. For mine, these six screws required a #9 Torx bit. But removing these 6 screws will not allow you to open the drive, yet. There is usually one more hidden screw, someplace under the label. Manufacturers do that to ensure that drives returned on warranty have not been tampered with. You can usually find it easily by running your finger over the label till you find a soft spot. That's where the screw is. Tear open the label and remove that screw as well.

With all of the screws removed, you can now pull off the cover plate and see that shinny disk you are after.

In this photo, you can see the reflection of my hand and camera as I took the picture.



But there are a couple of things in the way of just popping that disk out, and we need to get them out without damaging the mirror finish of the disk. Most noticeably, the arm that hold the head that actually reads and writes data to the disk. 

There are two heads, one on the arm you are seeing and another on an identical arm beneath the disk. The two arms are connected, so don't think you can just bend the top one out of the way and skip the removal process - you'll likely end up scratching the bottom surface of the disk. That bottom side will become important to you a bit later.

Fortunately, it is pretty easy to remove these arms. There are two screws that need to be removed. You can see them circled in red in this photo. BUT, we need to do them in the correct order. Remember, we need to do all of this without damaging the disk surface. So start with the small screw. It also uses a #9 Torx.

Once it is removed, you can remove the somewhat moon-shaped metal bracket that rests over the rear end of the arms. You may, at first, think there is still something holding the bracket in place, as you will find a noticeable resistance to removing it. What is holding it is the magnet that is on the underside of the bracket. You can easily overpower the magnet by hand, so go ahead. The photo at the right shows the bracket removed.

Next we have to remove the arm itself. To do that, using a large flat blade screw driver, unscrew the larger screw in the middle of the arm assembly. It won't come out all the way, but you will be able to tell when you have it completely free.

At this point, you need to rotate the arm out and away from the disk surfaces. Then you can easily (but carefully) lift the entire assembly out. Again, you will find a slight resistance, as there is another magnet at the bottom. Just pull the arm assemble out and set it aside.

We're getting close, now. The obstructing mechanisms have been removed. We just need to remove the rings that mount the disk to the spindle. To do this, remove the 6 or so screws on the top ring. You do this using, you guested it, a #9 Torx bit.

With the screws out of the way, you can remove the two rings. Now the disk is just lying there.

Time to start handling the disk itself, so I wore rubber gloves. Being used to handling the very fragile gold-plated mirrors, I found myself being very careful of it. In retrospect, I probably could have done without this - you'll be amazed at how tough the disk surface is. But, even the thought of letting that beautiful shiny surface get even a finger print on it prompted me to use an abundance of precaution.

To continue protecting the surfaces, now and during the upcoming cutting procedure, I covered both the top and bottom with masking tape. I then trimmed the tape so I could trace around the outside edge of the disk when setting up for the cutting.

To hold the disk securely and to further protect the disk surfaces, I sandwiched the disk between to pieces of 1x6. Since the disk was going to be hidden from view, I traced around the disk before assembling the sandwich. I also marked where the center hole of the disk was. All of this so I could tell where to cut the holes. You can hold the sandwich together in any manner you choose. I used a small finish nailer - one nail in the center and one at each corner of the boards.


Now it is time to set up for drilling. You need a 7/8" hole saw that is capable of cutting metal. Most hole saws have a center, or pilot, drill bit as well. Obviously, we don't want to put a hole in the center of each of our mirrors, so that needs to be removed. There is probably a set screw on the side of the hole saw bit that, when loosened, allows you to slip the pilot bit out.

You can use a hand-held electric drill if you wish, but if you have a drill press available, you will find it much easier. I chucked up the hole saw and set the depth to allow me to drill through the top board, through the disk layer, and a little bit into the bottom board.

There are probably other ways to construct this, and if I were going to be doing a lot of these, I would take time to design a jig to help with the setup. But for now, this is just fine.

Here we are making the first cut. Notice that I have the sandwich clamped down tightly to keep it from flying around if it happened to get away from me, had I only been holding it by hand.

I ended up cutting 9 mirrors, so I did a lot of clamping and unclamping. That's the price of safety.

To cut the mirrors, I ran the drill at 590 RMP. I would have like to go even slower, but 590 was the slowest speed available on my bench top drill press. Along with the slow saw rotation, you want to feed the drill very slowly as well, at least when you get to the middle of the sandwich where the metal disk is. The slower you go, the less burr you are going to create. I didn't go as slowly as I probably should have. Patience is a good thing here.

When you use a hole saw, the center plug (the wood and the mirror from the disk) will be inside the hole saw. To remove them, slip a small screw driver or other item in one of the slots on the side of the saw, and push the plugs down. The mirror will come out first. BE CAREFUL! THE METAL MIRROR WILL BE VERY HOT! (Don't ask how I know.)

When the mirror disk first popped out, I was sure I had done something wrong. It looked terrible. Fortunately most of what I was seeing was sawdust stuck to the masking tape I had used and the metal burrs around the edge of the mirror.

As this was the first one, I was anxious to see if there was anything salvageable at all. So I carefully removed the tape and sawdust. Denatured alcohol and cotton swabs did the trick nicely. To my great (and very happy) surprise, the mirror was in very good shape.  I went ahead and deburred the edge with a flat file.

NOTE: If I were doing this again - I would look for alternative means of holding the disk for drilling. This method works - but other methods might make cleanup a bit easier and faster and produce less burring. 

Below, you can see my new HD mirror on the right, compared the the gold-plated mirror I removed from the laser. Yes, the gold-plated mirror was getting ready to be replaced anyway, so the timing of this worked out really well for me. And the edge of the new mirror is a bit ragged. But that is OK. Remember, we really only need to use the center of the mirror where the beam will hit.

On my laser, all of the mirrors are 20mm in diameter. The 7/8" hole saw I used, has an interior diameter of only about 17.5mm. To make it all work, I cut a spacer ring out of 2mm thick craft foam.

I made it just small enough on the inside to slightly stretch over the new mirrors and the outside to just fit inside the mirror mount housing. This worked out beautifully.

The disk mirrors are just a slightly thinner than the stock mirrors I had been using. The only effect I noticed was that I had to readjust my alignment of the replaced mirror. Fortunately, the adjustment was easy and quit fast - taking only about 30 seconds to perform and the beam was dead on again.

You can't help but wonder what the reflective ability of the HD mirrors is compared to the original gold-plated mirrors. Before replacing the mirror, I did some test cuts with the old mirrors. I made a cut in 5.6mm acrylic. I had the power and speed set so that it would just barely cut all the way through on a single pass. In fact, I had to apply just slight pressure on the cut portion to get it to break completely free. I knew that if I used the same setup with the replacement mirror, I could get a sense of any power loss from using the HD mirrors.


When I switched mirrors and made the cut again, I was surprised to find that it cut equally well. In fact, it may have cut just slightly better! In the photo, notice the burrs on the lower right edge of the piece on the right. That was cut by the OLD mirror. The other, cut by the HD mirror, is clean. In fact, the surface of the cut is as good or better with the new one than it was with the old one.

I then cut some additional foam rings to use fore the additional mirrors I was able to cut from the HD disk.

Again, the cutting with the new mirror was identical to the cutting I had experienced with the gold-plated mirror.


I ended up with 9 new mirrors - one in the laser, and the 8 you see above. But Wait! I don't have 9 new mirrors. I have 18! Both sides of these mirrors are the same reflective material. In reality, the back side of a few were slightly damaged in the cutting process. All together, I ended up with 15 good, usable mirror surfaces.

If you are thinking the above arrangement of mirrors reminds you of a Christmas tree, that was intentional. After all, what better present can you get than a handful of free laser mirrors?

I haven't done any engraving tests yet. The cutting tests tell me there is not significant power loss, so the engraving process should be equally as good. In fact, Walt's engraving tests looked great. Again, a big thank you to Walt, who had the original idea to even try this.

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19 comments:

  1. Thanks for this - I will make up a few of these to have as spares as I seem to have plenty of scrap HDD but no spare mirrors!

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  2. Glad it was helpful. Currently, these are the only mirrors I use.

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  3. Thank you for posting this useful howto article, Its nice to know there is another source of Mirrors...

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  4. Awesome! I have been looking for "cheap" front surface mirrors for a laser show setup and you just made my day. These are perfect for a 3 motor Spiro. And... I have a box of ten or so "old" hard drives. You know, the 30-60gig IDE ones that I just couldn't throw away!

    Jules

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  5. Nifty idea!

    You should probably invest in a diamond core drill. Prices are very reasonable and the quality of your mirrors will improve. Bond the platter to a sacrificial piece of glass and use coolant.

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  6. Nice hack, would this work for Bluray diode cutters?
    Seems that these are great for cutting clear plastics, and general etching due to the increased absorption at this wavelength.

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    Replies
    1. Sorry. I don't have any eerience with diode cutters. If you try it and find it works, be sure to leave additiona
      Feedback

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  7. This is great!

    Just a word of warning - some of the smaller HD's have glass platters and shatter. Don't ask me how I know this ;)

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  8. Hello! I really like the idea and your post. I just have one question: Do you know how good is the performance of these mirrors at a AOI of 45 degree? Thank you.

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  9. The angle of incidence on all three in my system is 45 degrees. These are the only mirrors I currently use. I find them to be as good as the gold mirrors I used to buy. They are also tougher, meaning I can clean easier with less likelihood of damage, so they last longer. I am still on the first set I installed (14 months ago).

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  10. Hi,Thank for good idea.
    Do you think this mirror is usable as two-side of laser tube? I'm making one of "home- made co2 laser, and my plane is to use hdd mirror(combinated with N-salt OC)

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  11. Not sure what you mean by "two-side of laser tube".

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  12. Hi
    I'm sorry i forgot the details, this is a home made co2 laser tube. absolute.
    I mean two side of the resonator tube.
    Usually the output coupler is Znse .(I would like to use drilled hdd mirror(and Nacl window) and the other side, I've made a hdd mirror.
    Unfortunately, there is no experience, so I ask you.
    Many of the home made co2 laser's resonator are mounted with simple car-mirror, or hand polished copper plate.
    Do you think is the idea good?
    Pictures made ​​about the process.
    (a couple of pictures on my(temporary) site) but I did not put the link here without your permission.
    Thanks for answers
    Piq

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  13. Hello
    mirrors made with hard disks may be used with a power of 60/80 w co2?
    thanks

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  14. I don't have a 60/80 watt system, so I cannot say for sure, but I suspect you can. You will be amazed at how tough those mirrors are.

    If you try it and find differently, please let us know.

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  15. Hi. I'm new in laser cutting and I was wondering if I could use my laser to cut those mirrors? Just worried if mirror could reflect laser beam back.

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  16. I'm slowly building my laser engraver/cutter now. Found your blog while searching for cooling the tube. Thanks for posting these great articles and howto. They really help me out. This source of mirrors is great. I've been saving some HDD plates just because they are so beautiful. Now they can be used for laser mirors.

    One question about the wiring of the tube. I'm not sure if it matters, but which end of the tube is supposed to connect to the positive wire from the power supply?

    Thanks

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  17. The positive (larger) wire goest to the back end ops the tube. The small, ground wire goes to the output end.

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  18. Thank you for the answer, sir!

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