Week 03: Computer Controlled Cutting¶
This week’s group assignment is to characterize our laser cutter. At Fab Lab Bali, we use the FSL Muse Core, a 40W CO2 desktop laser cutting and engraving machine with a 304 x 508 mm work area.
Focus¶
Our machine has a fixed 2” focal length lens and comes with a billet to help set its focus. Here are the steps for setting up the focus:
- Place the material on top of the work bed. Larger material tends to have a little bit of bow and will affect the cutting performance and quality result.
- Move the toolhead on top of the material using the jog keys or by unlocking the toolhead and moving it manually.
- Place the billet on top of the material and below the nozzle.
- Hold the toolhead, release the locking mechanism, and let the nozzle rest on top of the billet.
- Tighten the locking mechanism and remove the billet.
Speed, Power, Current, & Passes¶
The control software can be accessed through a browser using the machine’s IP address when we are connected to the same network. We can import vector or raster files, make small adjustments (like sizes, add text, duplicate instances, etc.), and most importantly, adjust:
- Speed: Percentage from the max speed of toolhead movement
- Power: Percentage of power the laser tube delivers
- Current: Control the pulse of the laser; some machine may also refer to it as the rate or frequency
- Passes: Number of times the laser will run a layer
All the settings above will vary depending on many factors such as the state of the laser tube, the wattage, and the material itself. Before running a job (especially a large one), it is advisable to do a cut test first on a sample material to determine the optimal settings. For this, we use a file that Full Spectrum Laser provided to do a material test. It’s a simple file with a grid of squares with one axis indicating speed, another indicating power, each has 25% increment.
Here are our test results with their respective settings:
2.7 mm cardboard¶
| Setting | Value |
|---|---|
| Speed | 25% |
| Power | 40% |
| Current | 100% |
| Passes | 1 |
6.5 mm double-layered cardboard¶
| Setting | Value |
|---|---|
| Speed | 25% |
| Power | 40% |
| Current | 85% |
| Passes | 2 |
Evaluation¶
Finding the perfect settings is like an act of balancing. When you use a higher power value, then you can increase the speed because the laser needs less time to burn through the material. The opposite is also true: the lower the speed, the lower the power needed because the laser has more time to burn through.
The included test only varies in power and speed, which is adequate to evaluate many types of materials. When a material is too thick to be cut even with 100% power and 25% speed, then we can add passes instead of lowering the speed even further.
From the test result, you can see the settings that make a successful cut. Generally, you want to prioritize choosing the lowest possible power value and choose the fastest possible speed from the chosen power value. A higher power value tends to increase the width of the material that got burned. Even worse, running high power values at slow speed tremendously increases the risk of your material catching fire. We do not confirm nor deny that a small fire started when we were doing this assignment. (It totally did!)
For the current, we find it gives very similar results with power settings. One place we find it useful is for fine-tuning. When cutting a thick material that easily combusts like cardboard, we find that we need a certain power value to cut it through, but it tends to ignite and spread a little burn. We try to either lower the power or increase the speed, but it results in the material not getting cut all the way. That’s where lowering the current value a little bit helps reduce the chance of the cardboard starting to ignite while still successfully cutting through the cardboard.
Kerf¶
Kerf is the width of the material that got burned away by the laser. To find the value of our machine, we use the Kerf Checker tool by Doyo-sensei. It generates an SVG file that has a series of slots that start and incrementally increase or decrease by values that we defined.
We do tests for both cardboard options, and the following are the kerf values for each material:
- 2.7 mm cardboard: 0.2 mm
- 6.5 mm cardboard: 0.5 mm
Joint Clearance¶
By reducing the width of a slot by its kerf value, it results in the laser-cut slot width dimension matching the theoretical thickness of the material.
- 2.7 mm - 0.2 mm = 2.5 mm
- 6.5 mm - 0.5 mm = 6 mm
This slot fits nicely with the other piece; however, cardboard thickness varies slightly, especially the one we tested, resulting in some of the pieces fitting slightly loosely. Luckily, cardboard has slight elasticity, and we can reduce another 0.1 mm on our slot width, and we will get a tight connection.
