Now that the laser is firing all the way through the beam path and the path can be controlled by the computer, we're down to the detail:
Controlling the Laser
I don't have too much to say here because I got incredibly lucky and someone else did all the heavy lifting for me.
Users on Buildlog.net have done lots of work making it possible to control the laser from EMC2. User BenJackson has published his configuration files and adapting them to my machine was a piece of cake.
His configuration file includes a custom HAL component that does PPI (pulse per inch) control. With this configuration, I have three "knobs" I can turn to adjust how the laser cuts or engraves material.
- Feed Rate controls how fast the laser is moving over the material
- PPI controls how many 3ms pulses are delivered for each unit of travel (inch or mm)
- Laser Power. EMC2 can vary the PWM signal to the laser power supply to control the power delivered to the tube.
By playing around with these three, I've found I can go from drawing a light brown line on a piece of paper all the way up to burning clear through 5mm wood or 1/4" acrylic! Very Nice! I've got plenty of learning still to do but it's looking good.
The basic buildlog setup is a 5 gallon bucket of water, and an aquarium pump. I need to tidy up my setup but it's working for now. The only part I'm missing is a flow switch. The control card has an input for a switch that is tied into the safety interlock. It should prevent the laser from firing if the water isn't flowing. I don't have a switch yet so I've hotwired around it. Not good.
The glass tube hanging off the back makes me nervous. I'm not sure if there's any dangerous radiation emitted from the sides of the tube, but I'm not taking any chances. Besides, it's just a matter of time before I drop the broom handle or something else on to the tube and bust it. I had a local sheet metal shop bend and weld up a shroud that fits over the tube and screws to my mounting rails. After painting it, I think it came out nice.
When the laser is burning anything, and especially plastics, it puts off a lot of smoke and foul smelling crap. I have a big dust collector for the CNC machine. I'll add a drop near where the laser will end up so I don't have a dryer hose trailing across the floor.
And the results? This is 1/4" plywood cut through.
Since my tube mount is completely custom, I have to manually align the tube with the first mirror. The C02 laser is invisible (and dangerous) so aligning it correctly can be a trick. I saw a solution on buildlog that I thought was a very clever hack. The guy used a reprap to print out two disks the same diameter as the tube. One disk has a very small center hole, the other has a hole that exactly fits a laser pointer. He mounts them in the brackets and adjusts the laser to shoot through the small hole, into the first mirror. Once the alignment is correct, he loosens just one screw to remove the disks and insert the tube. At that point, the alignment should be very close.
I have a reprap but I had some time to kill before Christmas while I was waiting for my power supply to arrive and needed some lathe practice. I turned these two 'cookies' and bored one to fit a cheap laser pointer I have.
Not much to say about this. It's scary cool! The tube glows pinkish purple and the wood block ignites instantly. The only thing I've seen ignite faster was the imagination of my 12 and 10 year old sons. Something about that glow inspires a guy to try stupid stuff. Fortunately eye-protection was the order of the day and no injuries were reported.
Since I'm replacing the RF tube with a Chinese glass tube, I'll have to fabricate the mounting brackets. The buildlog 2.0 laser uses plastic brackets cut out of HDPE on a CNC router. I've cut HDPE before and it's great stuff to work with on the router and I even have enough left over from an earlier project.
I started by mounting two pieces of 1/8" aluminum square tube to the existing mounting holes on the frame of the laser. This will give a nice solid base to attach the brackets to. It also has clearance behind for routing wires and enough room to turn the bottom adjusting screw.
The old panel had an LCD display and a few controls specific to the original electronics. It went away with the rest of the antiques.
I made a new panel from a chunk of 1/8" steel cut to the same dimensions as the original. I consider this a temporary job to get the machine up and running. It has a bare minimum of control since most of the user interaction will be done through EMC2 on the PC.
Ultimately, I'd like to incorporate some controls to jog the X and Y, touch off, and monitor the water temperature, but that can all wait. This panel will have the following:
The all-important Emergency Stop button. (E-Stop). A good E-stop is is big and red so it's easy to hit. It also locks into the emergency condition position. There's a lot of different styles available and they can be very expensive. This one isn't expensive. It's also cheap. It has two sets of terminals so the switch can be wired normal-open or normal-closed. Playing around with it, I found the normal-closed was reliable but the normal-open was flaky in the closed position. I certainly wouldn't trust my life to this switch in that configuration. The way I'm using it, any flakiness will shut the machine down.
The toggle switch/button toggles the controller between taking it's pwm control signal from either the potentiometer on the panel, or from one of the pins incoming from the computer. For normal operation, the computer will control the output power of the laser but manually controlling and firing it is desirable for alignment.
The pot (black knob) sets the pwm manually as described above.
The square momentary switch manually fires the laser. Useful for alignment and other 'experiments' (ie screwing around 🙂 )
I drilled and countersunk holes to mount the panel. Then mounted it on the machine. Then overlayed it with a sheet of paper and played around with where I wanted the controls before drilling and mounting them.
After drilling, painting, and installing:
Well, not quite....yet.
I found an old Universal Laser Systems model 25A for sale at a surplus auction. It looked to be in good shape and went cheap. After I got it home and cleaned up, I found that I couldn't get the laser head to fire. I called in some expert assistance from Columbia Gadget Works, but no luck was to be had. I've since learned that RF laser tubes have a life expectancy of about 10 years before they need to be re-gassed. Re-gassing this one is prohibitively expensive and would *only* get it back to 25W. Instead, I'm looking at replacing the RF laser with a chinese glass tube. This should take it to 40W.
Either way, this looks to be a fun project. Here's a picture.