When using Linux EMC I could easily drive a laser from the direction pin of the Z axis on the parallel port.The pin held it last state so if the last movement commend was down it stayed that way even as the other axis' were moving. All I had to do was wire that to the laser enable lead.
When I switched to GRBL I found the dir pin always reset to up whenever another axis moved. this strange interaction did not affect the stepper because there were no pulses on the step pin. all that was needed was a simple d flip flop to keep the state. it turns out a 12c508 pic micro is cheaper than a d flip flop....
Step 1: Assembly
I added a bi color led so i could see the laser status without having the laser connected. then I added a 3 pin jumper to select direction pin polarity.
if you are using a dedicated laser engraver this wouldn't be necessary as you could change the polarity of the pin in software. I use my machine for both laser and milling/engraving so I wanted an easy way to match it to the setup of the z axis of the mill.
I have used this circuit with a 2n2222 to drive a mechanical relay, with a 2n2222 pulling a p-channel mosfet, and with a solid state relay. the method you choose depends on your laser system.
Step 2: PROTECT YOURSELF!
The first and most expensive investment you will make is a quality set of Laser Safety Glasses. This is not optional.
Step 3: The Laser
There are many types and sizes of Lasers. The first one I experimented with was salvaged from a DVD burner. It was about 350mW but was a little weak for what I wanted. It would easily burn anything dark but had trouble with light woods and cork. I wanted to engrave the cork in the bottom of drink coasters.
Step 4: The BIG Laser
I eventually moved up to a 5W diode laser. That one made a lot of
heat but I had a heatsink from an old Mac. The old PPC Mac's had really nice heavy all aluminum heatsinks. The one I chose had a raised boss where it touched the chip. That turned out to be the perfect size to hold a to-3 device.
Step 5: Heatsinks and Optics
These things make plenty of heat so you need a may to mount them. The most common types are TO-18 and TO-5 cans. These can both be used in their matching 12mm laser housings. Thats the easiest way to get a sturdy mount and optics in one package.
I bolted a couple of scraps of aluminum block together with a couple of index cards in between. I then milled it flat on all sides and bored a 12 mm hole down the middle. That made a good mount to go to a pentium II heatsink with its fans attached.
There are also T block mounts available but there is less contact area that way. By boring the hole with index cards as a spacer it made a very tight fit around the module when the cards were removed and discarded. Modifying the T blocks for a pinch fit is possible but with < 1W lasers a little extra grease seems to be good enough.