"The Laser from HELL"
I have been playing with a low cost diode laser etcher/cutter since last summer. Everything about the machine is marginal and my lack of knowledge in this arena has really hindered progress. I ended up developing a Linux application to control the etch/cut operation, built a circuit board to drive the electronics, and developed embedded firmware to run the generated gcode.
I suspect 3D printer users experienced similar pains getting started but that industry is much more mature and stable. The diode lasers are low power, -0.5W to 6.0W, devices that evolved from the BlueRay DVD technology. Add to the equation the safety elements and the inablity of the Chinese vendors to tell the truth and we have a product in complete chaos.
I belong to an online group with over a 1000 members dedicated to this technology. Almost every new member (including me) started with "I bought a low cost laser cutter fro China and it:"
- Arrived without documentation
- Failed to work
- It ran for 23 minutes and died
- Where is the host software
- Where is the controller firmware
Due to the small size and light weight the typical mechanical structure is quite simple and robust where they can't screw it up. Individuals and companies have added the diode module to CNC mills and 3D printers with varying degrees of success but the cost of the standalone diode module often exceeds the cost the the entire kit.
The typical controller uses the GCODE protocal to request X,Y,Z motion and laser ON/OFF. Depending on who developed the particular gcode variant, theirs is the "standard" and everyone else is a deviant. Or their is "custom" and it is better than the standard. Regardless there is no industry reconized standard. Most implementations agree on the simple motion commands, are somewhat close on simple configuration, and completely disagree on anything relative to laser ON/OFF commands. Please note that I use the words "typical" "simple" "standard" with a large degree of cynicism.
While they both are lasers, the diode laser is quite different from the higher power CO2 lasers in regard to operation, speed, and materials that can be cut.
The ability of the laser to cut (burn) is dependent on three factors:
- Laser power
- Laser beam focus area.
- Applied time.
In addition we want to vaporize the material, not ignite it.
We can somewhat control the laser power by either pulsing the laser ON/OFF via PWM or varing the speed. I prefer the PWM method.
The laser needs a constand current source and that means a dedicated drive board. Often the analog circuits on these board distorts the PWM signal produced by the CPU. The typical systems use a power MOSFET on the CPU controller board and switch 12V to the diode module. Then they cut corners and marginally drive it resulting is a short product life expectancy. Perhaps the real profit is in replacement boards.
It is also necessary to adjust the stepper motor driver current limits to obtain optimal smooth motion. In that the motors are about as weak as they can be this is another marginal component. I have fried 4 driver boards in 6 months. Must be another high profit component.
After 4 months of frustration I started getting some reliable results. Once the hardware stabilized I was able to tune the application and firmware to fit my needs. My ecpectations were also downgraded. One thing that is quite a positive susprise is the position repeatabliity. The stepper motors take 80 steps per mm and I and quite sure that the system can maintain that accuracy.
I have been successfull cutting up to 3mm plywood, 3mm bass wood, 2mm balsa, 3mm colored ABS, 0.15mm mylar, plus standard white printer paper, card stock, and synthetic shelf liner. For etching I have used wood, slate, anodized alumimum, painted metals, and cardstoke. BTW - Neon colored cardstock is my favorite test material for both cutting and etching as I can use low power and high speed and it is cheap,
Greater than 1mm cuts typically require multiple passes. The laser will lose focus within a 3mm cut. It also means that the cut will be wider and more charing on the walls.
Another learning experience is not all laser diodes focus the same and there are multiple lenses available. It fact, due to the manufacturing technoology, 1.6W laser focus the best and 5,5W focus the worse. Guess which one I bought!! Turns out a properly focus 1.6W laser will outperform all the others for cutting. Remember it is the power delivered to a point and the sharper the point the better the cut.
I receintly added X & Y limit switches and needed insulating spacers. I have a roll of synthetic shelf liner which is about 1mm thick and used the laser to cut the pattern with minimal effort on my part. Best part was I need one more and that was about zero effort.
While I bought it to cut 3mm ABS my primary interest has turned towards etching. The kids building blocks were purchased from Hobby Lobby for about $1.00US each and were Christmas presents for three little girls. I spent (wasted) way too much time getting gimp to produce an etchable alphabet. The letter gets etched on 4 faces of the block and small circular magnets get embedded in the other two. My 15 month old granddaughter like to stack the vertically. The letters are etched wit a left->right followed by right->left raster burn operations. The start and end points are quite precise.
I also got interested in etching slate coasters. An online acquaince posted a Dobby Elve image that consumed and infinite amount of time for me to etch in slate, all just getting the text right. After multiple revisions I now have a recipe for adding etchable text in gimp and burning in slate. Only 1 slate coaster compeletely ruined plus two that didn't look quite right before the finished product.
I am clearly addicted to this technology. Have a couple spare laser modules plus plans for making a much larger frame. The online group at www.benboxlaser.us is a great resource. While 99% of the users log on to get help getting started and then disappear, the remaining 1% is quite active.
I should mention that I bought my 5.5W laser after seeing a video of it cutting 6mm (1/4 inch) clear acrylic. Turns out the video is pure fraud. First there is insufficient power and the focus cannot be maintained over that distance. Second and more important, laser diodes at 440 nano meters just pass thru clear plastic. They used a CO2 laser at 1100nm were and photoshopped the video.
My next step is going to require a 3D printer. I have one that has been almost assembled for about 2 years. After that I will be heading down the CO2 laser cutter path unless there are better diode options.