Saturday, November 29, 2014

Laser for ShapeOko2.

I have been thinking a lot about how to install a laser in the ShapeOko2 machine I assembled a few weeks ago.

In my mind, it should be capable of delivering enough power to the focal point to impress a photoresist coated PCB or even evaporate the ink from a black, hand painted PCB. Maybe it will also work with black wax coating too.

The list below converged after many days of EBay browsing. Keep in mind that there are many suppliers for each item. I tried to select the ones that looked better and cheaper for me without compromising quality but I may be wrong and only the tests will tell if I succeeded. Also do not forget that there are laser diodes and laser diodes. They look pretty the same, but their quality can vary a lot.

If you ever want to start a new hobby and it involves lasers like this, YOU MUST READ ABOUT LASER SAFETY. The most important thing to know and always remember is that YOU CAN GET PERMANENTLY BLIND IN A FRACTION OF A SECOND. My masters advisor always remembered the students that WE HAVE ONLY TWO EYES and WE CAN BURN BOTH IN A SIMPLE, STUPID, ACT LIKE LOOKING AT THE REFLEXION OF A LASER BEAM IN A METALLIC OBJECT. In laser science, research labs avoid reflexive materials and scientists are advised to keep the laser beams in a very definite plane and to keep their eyes far from that plane.

You must also wear protective equipment every time you enter a room with a free propagating laser beam. Special goggles are made to absorb all the light from the laser that you are working with. This means that, different laser colours may require different safety equipment. And this rule includes far-infrared (CO2), infrared and ultra-violet lasers. The fact that you do not see the laser beam, or that it looks faint to your eyes, does not mean that they are safer. It is the contrary. They are much more dangerous. INFRARED AND ULTRAVIOLET LASERS CAN BURN YOUR EYES TOO. THEY ARE VERY, VERY DANGEROUS.

So, think twice before starting this new hobby. Enforce safety on the working environment punishing who enters it without protection with a one day entrance denial, or a many day one in case of recurrent behaviour. Remember all the beautiful scenes that the people will miss in their future if they loose their vision if you need motivation for this.

Before continuing read the information on this link and on this link too.

One last call to safety: if you look at the sun your eye hurts, right? The sun delivers to our planet around 1.4kW per square meter. This means 1400W per 1000mm x 1000mm area, or 1.4mW/mm^2. A typical, low power, cheap, red laser pointer delivers 1mW per square mm. It has roughly the same intensity as the sun but it is even worse for your eyes to look at a laser beam than to look at the sun. Check this link to see why.

I hope you understood that you should not keep reading this post before reading all you can about laser safety. And that YOU SHOULD NEVER POINT A LASER TO ANOTHER LIVING CREATURE WITH EYES. You can blind your cat, your dog, your neighbour or somebody you love in a fraction of a second.

Now let me share with you what I just bought on EBay. The list includes power supplies, drivers with TTL port, 405nm and 808 diode lasers, copper laser housings, a heat sink and lenses for both wavelengths. The power I chose for the diodes was 120mW (405nm) and 500mW (808nm). Both are very powerful lasers that should do a lot of damage when focused to a 0.1mm spot.

Let me start by the laser diodes. As said before, I chose two wavelengths. The first, 405nm is the peak of absorption of photoresist materials that coat PCB boards. The second, 808nm, is the peak of absorption of copper. Above the selected powers the prices seem to increase a lot so I selected the best relation power/price for me.

808nm 500mW 5.6mm TO-18 Infrared IR Laser Diode No PD        $6,54 USD

New 405nm-410nm 120mW TO18 5.6mm Sony Laser Diode/Violet Laser Diode 1

PCS         $7,99 USD

These diodes must work at around 25 degrees Celsius. If their temperature increases, their lifetime decreases abruptly. They need the operation heat to be flowed out very efficiently, so I selected housings made of copper, that seems to be of good quality:

3 pack 12 x 30mm Copper 5.6mm Laser Diode Mount Blank Module & Diode

Press Tool         $28,00 USD

After being assembled on the housings you have what they call a laser module on EBay sellers language. The module needs to be inside a heat sink. The higher the laser power, the better must be the heat sink. Some of the heat sinks even accept fans. So I selected this:

New TYPE Professional Cooling Heatsink/ Heat Sink for 12mm Laser Diode

Module         $5,99 USD

You also need lenses to collect the light emitted from the diode and collimate it to a beam. As you may not know, the diode does not emit light in a straight line. It is more like a cone. The lens must be placed with its focal point positioned over the diode output and it must be transparent to the light emitted by the diode. If possible, it should have an anti-reflective coating to avoid loosing power by backward reflection. I selected two lenses, one for each wavelength:

For the 405nm (purple, UV) laser:

445nm 405nm Three Element Glass Lens for Aixiz Module        $10,95 USD

808nm 3 layer Glass Laser Collimation Lens with M9P05*10mm Frame        $4,99 USD

The laser diodes requires constant current supply at a specific voltage. The parameters vary with the emitted wavelength and there are ready made circuits to drive them. I chose drivers that can be tuned, hoping that I can decrease the emitted power to a minimum while learning how things work. My options were:

405nm 50mw-400mw Violet/Blue Laser Module Power Supply Driver 12V with

TTL         $14,23 USD

Professional Laser Diode Driver for 808nm&532nm +660nm with TTL        $14,39 USD

Finally I ordered two power adapters to feed the drivers:

Power Supply AC 100-240V To DC 12V 2A Adapter for 3528 5050 LED Strip

Light EU         $4,39 USD

AC Converter Adapter DC 5V 3A Power Supply Charger EU plug 3000mA MICRO

USB 15W         $5,49 USD

 

This post was long. I will share my results here as soon as the parts arrive and I assemble them.

Thanks for reading.

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