Laser Diode Housing from Hardware Store Parts

{adinserter Internal_left}I never seem to be able to finish my laser engraver/cutter from broken DVD-RW drives project (inspired by Groover’s pocket laser engraver) because I keep opening new DVD drives and keep finding reasons to go on tangent mini-projects. Most of those mini-projects are brought about by my admiration of the amount of useful parts a DVDs has (even a broken one, apparently) and some are caused by specific challenges each new opened drive brings. So, at some point I opened an HP SDVD8821H DVD R/RW/RAM Drive and found this laser diode inside:

It’s a weird looking laser diode (LD) that is mounted in the same case with the photodiode arrays which makes for simplified optics but I did not have any housing for this shape/size diode. By the way, if anyone reading this knows a professionally made housing for this type of LD, please post a comment with the reference, I would greatly appreciate that. The diode is just slightly smaller than your more standard 9mm LD – it’s smaller diameter is 6.50mm and the larger diameter is 8.25mm so it fits neither 5.6mm nor 9mm standard size housings.
This made me think that I may not be the only one stuck without a proper housing for a laser diode and I decided to see what it would take to build a housing for a laser diode out of parts available only in the disassembled drive itself and in a local hardware store. Here is what came out

Please note that this housing is not for collimating the beam (i.e. not for laser pointer – type beam), this housing is for focusing the beam on the material you’re cutting/engraving. Additionally, these lens are more of a concept than a finished product – you may be able to do much better than I did if you, for example, use washers with a larger internal diameter (or drill it to a larger diameter) to allow more light through and therefore stronger beam at cutting point. So use this as a source of ideas for your own laser lens build. And be careful: USE PROPER LASER SAFETY GLASSES !!!

You will need these parts from a hardware store (mine came from Lowes):

• #6 washer (3.95mm internal diameter, 9.70mm external diameter if you don’t use US standard sizes) from the fasteners section
• Two Compression Nuts with inserts for 1/4 OD tubing from the plumbing section. Confusingly, its internal thread is called 1/8″ FIP ( Female Iron Pipe )
• One 1/8″ MIP ( Male Iron Pipe ) – threaded Brass Pipe Nipple

As far as tools/ consumables, you’ll need superglue (I prefer the gel version of it), pictured. Also 7/32 nut driver bit, tweezers, pliers, a soldering iron and a bit of heat shrinking tubing to make it all look prettier in the end.

We need to start by harvesting proper lens from the DVD drive itself. Due to the tiny size of its optical tract most of the lens are actually Fresnel lens (they look almost flat) and have VERY short focal distance, impractical for our project. However, all drives have one plano-convex lens with focal distance of approx. 40mm which is a good size for this project. These lens are located between the beam splitter/combiner cube (it’s not exactly in the shape of a cube in all drives, so look carefully) and the mirror that sends it towards the CD disk. This lens is usually relatively easy to get to and often only holds in place by a plastic wedge insert. But you may also encounter some glue as well, so be careful and look around before yanking it. Try not to mar the surface of the lens – it needs to be very clean to produce a strong enough beam.

We need two of these but, since the CNC laser cutter project requires you to disassemble at least two DVD drives, you should have enough of these lens. Just be careful not to break any (or get a spare broken DVD drive for just in case)

Once you got the lens, use a toothpick to distribute small drops (just smudges, actually) of the gel type superglue around the inner hole of the #6 washer, then, using tweezers, strong>carefully drop the lens curved side on the washer, trying to make it well-centered relative to the washer. Flat side on washer works, too but if you drop the curved side down the lens appears to sit better – maybe it displaces extra glue to the sides easier than if it was the flat side down. Center the lens against the washer before dropping it on the washer. Because of the glue you won’t get much chance in centering the lens once it touches the washer.

While the glue is drying on the lens, use vise and the 7/32 nut driver but to press the diode into the compression nut’s larger diameter insert. Note that the smaller diameter insert may very well work for a standard 5.6mm diode if you cut the insert carefully to shorter length. I did not have a standard 5.6mm diode to play with but the size of the insert seems just right for press-fit a standard diode in it. Experiment!

After that use the vise again to pres-fit the insert back into the nut itself. The position that works just happens to be the reverse of how the insert would be positioned in the nut if you were attaching a 1/4″ tube to it but it holds inside the nut quite well anyway.

At this point you can put some heat shrink tube on the back of the diode to protect it during the following operations but I guess you can say this step is optional.

Next step – drop the first washer with the lens on it onto the bottom of the nut making sure that the lens’ curved side faces up. Then the nipple screws into the nut.

Put the second washer with the lens (again, curved side up) ontop of the nipple and carefully screw the second nut onto it. The washer diameter is just right to get itself centered relatively well inside the nut. So, if the lens was glued on well-centered, it should still be well-centered after all the threads are screwed all the way in.

And here is the finished housing with the diode ready to be plugged into your favorite laser diode driver and start burning something. I should once again point out that this housing was intended for fixed and relatively short (40 mm) focus situations – works well for cutting, does not work at all for laser pointers. Since the pipe thread is tapered, it only works when you tighten it all the way in (does not hold well until tightened) and so it would be hard to use this particular set of hardware to change focus. If you have to use this kind of housing, you’ll have to adjust the distance between the bottom of the housing and the top of the material you are cutting / engraving to 40 mm.

Here is a picture of the LD in action before I added the heat shrink tubing to the back to protect the contacts. The weird contact configuration is apparent on this picture. Also, I should note that the focus achieved is not so horrible as it looks on the picture. There is a lot of rather bright red splatter, which is what my camera picked up but in the center of it is a small (0.1-0.2 mm) bright spot that burns black craft foam.

I also should point out that there are lots of disadvantages to using such a crude housing. I would say that in reality you might use it to start your laser cutter project going, work on the mechanical and CNC parts, and do some test cuts/engravings. All the while waiting for the professional housing you’ve ordered to come in the mail (’cause if it comes from China, it will take a while). You will save a lot of frustration by using a good housing because it will be able to convert more of the laser diode’s power into cutting at higher speeds, wider range of colors and thicker materials. But, once again, the crude housing described here should at least get you started.

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