25 Balloons vs a 30W laser diode. Following in the footsteps of other laser enthusiasts who turned their lasers onto balloons we wondered what would happen if we did the same with one of our 30W laser tubes. With 60x more power at our finger tips we felt sure that we’d produce some spectacular results. The reality was a little different but we had fun with our experiments anyway.

We started by wiring up the laser tube to make sure we could test fire it without any additional control signals. The Laser power supply has a ‘test’ button on it which is a good place to start. Safety is all important when playing with high voltages so we made sure the wires were well insulated with thick silicon tubes and the laser itself had a silicone tube covering the anode. Even though we were only doing very short bursts of laser we didn’t want the tube to heat up so we also installed a water pump and had water flowing through the cooling jacket. With the laser tube plumbed in, a quick test fire of the beam ensure that we were getting lasers out of the right end of the device.

The balloons were inflated by an enthusiastic bunch of onlookers. After a few test shots at 2-3 balloons, 25 balloons were inflated and stapled down to a wooden batten. This ensures that the balloons all remain in a straight line and that they won’t be blown out of the way as the previous balloon pops. Black balloons absorb the all the light hitting it so the theory follows that black ones should pop more easily. With the balloons lined up, the laser ready to go we took our best shot and the row and the results are shown in the video above. 25 balloons all popped in a single firing.

This was a pretty fun and silly way to spend an evening. If we’re honest it didn’t blow away as many balloons as quickly as we had hoped but there are definitely some major improvements we could have made to the process.

• We under inflated the balloons to fit more of them into the limited space we had, thicker rubber is harder to burst.
• An additional lens on the laser tube would have kept the beam in focus for longer, meaning more popping power.
• The balloons still moved around on the baton as they popped, you can see at the end some even managed to pop out of order.
• With more time and more space we could have set up more balloons.

One of the limitations with hobby sized laser cutters is that the cut can only be made vertically through the material. It is possible to buy machines with more cutting axis but they are outside the budget of individuals. This means that for home brew mitred joints we have to be a bit more creative. If moving the laser beam to a different axis isn’t possible then how about moving the material we’re cutting through?

Here at Just Add Sharks, we’ve been running some experiments using these cutting jigs and the results are pretty promising. The first and arguably most useful jig holds the material at 45 degrees to the laser beam. The panels that make up the box were cut to size before the machine was set up to accept the mitre jig. The laser was focused to the top surface of the material while at an angle and the power set to cut material 1.4 times thicker (the thickness of the material at 45 degrees).

While using the mitre jig the laser is only capable of cutting in straight lines, any deviation off the cutting line takes the material out of focus. Each side of the each panel has to be cut individually, so the panel is manually rotated within the jig after each cut. The jig is arranged so that the panel remains the maximum size and the external dimensions of the box will be the same as the panels.

The flat spots on either side of the jig line up with the surface of the angled material. The laser is focused to this height which is best for cutting the angled material. The lines on either side show where the cut will be made, the jig is aligned by ensuring the red dot touches both of these lines as the laser head moves from left to right. The jig is held in place under the laser beam using magnets to ‘lock’ it onto the honeycomb. The laser is programmed to perform a short cut in a single straight line, this should be just longer than the panel being cut.

With the first jig we underestimated just how much cutting power would pass through to the material underneath. After half a dozen passes the verticals had been cut trough and the base has some serious damage to it so the jig was redesigned to remove all the material from under the laser beam (common sense really). A panel was also placed between the verticals to give the angled material a flat surface to rest on, the meant no more balancing of panels between the verticals. The first, 45 degree, cutting jig can be downloaded here.

With the basic jig proven and working we were able to consider some other angles. Simply changing the verticals of the jig we were able to create the Octahedron (available here) and the Icosahedron (available here). Manually changing the angles like this is tiresome so the next sensible upgrade would be to build an ‘any angle, any material thickness’ jig for the same purpose, but that is a job for another day.

Here is a new height adjustment tool for the Blacknose laser. This tool features an image showing exactly where it should be aligned against the cutting head. (dxf here)

What happens when you combine a love of laser cutters with a love of cool 70’s toys and an Arduino? An ‘Etch A Sketch’ controlled laser cutter of course! I always wondered… what if I could control my laser cutter just like drawing lines on an ‘Etch A Sketch’?

Over here at Just Add Sharks, we’re celebrating International Arduino Day by dusting down one of the ideas we had a very long time ago! We present to you the ‘Etch A Sketch’ controlled laser cutter!

https://www.youtube.com/watch?v=huxarKnxWU4

Using our Blacknose Laser Cutter we bypassed the control board to drive the laser tube and stepper motors, an Arduino Pro Mini controller was patched into the machine’s wiring using the existing connectors to interface with the Leetro controller. Safety is important, using the existing wiring meant that the laser won’t actually fire unless the water pump is running and the lid is closed. The laser power is hard coded and it can be set to either cut through the material or just make a mark on the material surface just like an Etch A Sketch!

The handheld Etch A Sketch controller is custom built from laser ply and stained red with Mahogany wood dye. The screen is a layer of baking paper to give it a frosted plastic look. The dials are rotary encoders with quadrature output, the knobs are laser cut then glued onto the shaft of each encoder. The back of the Etch A Sketch was closed with more layers of stained laser ply, the final piece has 6 layers of ply and is 18mm thick.

The schematic above shows the connections we made into the control system. The onward items like the stepper motors or laser tubes have not been drawn because they were not modified and use all the existing wiring. The Arduino pro mini works as the controller. The analogue input pins are configured for use as general IO to provide the additional number of inputs required from the rotary encoders. The pulses for the stepper motor drivers are provided by the Timer 1 PWM hardware module. The laser module power is controlled by Timer 3.

The software is relatively simple. When the machine is turned on the laser will attempt to drive to the zero position. Both X and Y axis are driven until they hit the end stops. Once both axis are pressed against the limits, the controller moves the axis forward again until they no longer press the switches, this is the Zero/Datum position. From this known position the controller moves the laser head to a ‘Home’ position which is a fixed distance from the zero spot.

When the laser has reached the Home position it is ready to run. The stepper motor drivers require far more pulses than the rotary encoders provide. If it was left with a one to one relationship you would need to turn the dial a dozen times to get noticeable movement on the axis. The software detects rotation on the dials and creates stepper motor pulses for a set period of time, this scales up the number of output steps for each input.

The laser driver has its PWM input permanently set, the laser only turns on when the enable line is pulled low. As long as the laser is only turned on while the axis are moving, we eliminate the burning problems from keeping the laser in the same place. If the laser is run back and forth over the same area it will cut deeper and in the end that would cause a fire. Hopefully common sense on the part of the operator will prevail.

The source code to accompany this project can be downloaded here: EtchaSketchLaser.zip