3. Computer Controlled Cutting

This week’s group assignment was to characterise our lab’s laser cutter and to measure the kerf size to account for joint clearance.

1. Characterise FabLab Kamakura’s laser cutter

Laser Cutter at FabLab Kamakura

- Model: Trotec Speedy 300, 30watt CO2 laser cutter
- Work area: 610 x 305 mm (24 x 12 inch)
- Maximum material thickness:
-> 170 mm (6.7 inch) with 1.5 inch lens
-> 157 mm (6.2 inch) with 2.0 inch lens
-> 144 mm (5.7 inch) with 2.5 inch lens

Preparing the data

First we prepared a simple square shape on Adobe Illustrator and saved it in svg format.

We set the thickness of the line to be 0.001mm, and since it’s a Vector line, the color of line to Red (R: 255, G:0, B:0).
If we also had Rastor data, we would change those colors to black (R:255, G=255, B=255).

We then sent the data to Trotec by selecting “Print” from the File tab, and selecting “Trotec Speedy” as the printer.
- Select the checkbox “Ignore Artboards” - this ensures the printer will ignore the blank areas.

After we select “Print”, the Trotec window will open, with the print job sidepanel on the right. Drag and drop the desired job onto the work window.

Laser cutting

1. Turn on the machine, and wait for it to calibrate.
   

2. Place material inside (laser starts from top left). Tape the material onto the bed with masking tape as necessary.
   (Caution: Do not place a metal object on the bed as laser light can reflect on the metal, which can be dangerous)
   

3. Click the ‘Connection’ Button on the bottom right to connect the PC to the laser cutter.
4. Set the laser to the origin point, by using the machine control pad to move the effector along X and Y asis.
   

5. Focus the laser using the laser focusing tool.
   Raise the bed using the Z axis control button until the tool drops from the groove.
   
   

6. Make sure your data is aligned with the laser’s position (usually bottom right of the cross).
   

7. Close the lid.
   

8. Set the laser’s speed and power by first right clicking the work area, then selecting “Material Database”. For each line color, set the process (Skip/cut/engrave), Speed, and Power.

   • Speed is measured in milimeters per second
     
   • Power is measured in Percentage of 100%
     Note: The optimal settings for the old printer are displayed next to the printer in FabLab Kamakura, which is a good reference point to start from.
     

9. Press start
   

Important safety precautions:
※ Never leave the laser-cutter machine unattended during the printing process!!
Know that laser-cutting comes with risks of unexpected fire.
※ If a fire starts, be careful with opening the lid as oxygen can be fuel to the fire.
※ If it’s a little fire, you can open the lid and extinguish it appropriately such as blowing it out (if it’s very small), or covering it with non-flammable material.
For more extreme situations, there is a fire extinguisher stored next to the machine.
※ In case of emergency, press the red Stop button.
※ When printing, don’t directly look at the laser light.
※ Keep the room well-ventilated (open window) while printing, as the fumes produced from cutting materials can produce harmful gases.

Once the cutting is finished, turn the laser off, wait a little, and open the lid to see the final result.

Result

Vector (Red line):

Rastor (Black line):

We were confused by the result of P=90 S=100, which should have come out much lighter, but we figured that it was because of the raised board.

We concluded that the optimal settings for cardboard is below;

Type of image	Optimal Power	Optimal Speed	Memo
Vector	35	1.2	FabLab cheat sheet for the old machine recommends P=60 but as it’s a new machine, we need much less power.
Rastor	90	40-60

2. Press-fit test

The goal of this assignment is to identify the optimal “offset value” needed to account for the kerf.

What is a kerf?

• It’s the small width of material removed by a laser beam when cutting. They are typically 0.8mm-1.0mm
  
• It’s important to account for kerf width, as it can affect the fit of the final design (Good joints typically require 5mm). It also can help reduce waste and material costs.
  
• Some of the factors that affect kerf width are Laser type, the material, cutting settings, etc.
  -making@stanford

Preparing the data

Since the material we will use for this week’s assignment is cardboard, our goal is to find the optimal offset value for cardboard, for the Trotec 300 in Kamakura.
First we measured the Cardboard thickness using a caliper, and it was 3mm.

We then used this tool (developed by Mr. Daisuke Doyo in Fab Academy 2018) to create the test comb image data for testing.
We decided to do the test in 2 steps, first in wide intervals of 0.05mm between 200mm and 300mm, to identify rough fit, and then do a more precise test second time if needed.

Laser Cutting

The above data was exported as svg file and imported into the printer.
For the cutting settings, we referred to the results of above test, which is;

Vector: Power = 35, Speed = 80
Rastor: Power = 90, Speed = 40

Result

We assembled the parts together test the kerf and here are the results:

Slot size	The fit
More than 265mm	Too loose
255-265mm	Fits well
Less than 255mm	Possible to force it to fit (since cardboard is flexible), but creates bends

We concluded that the optimal offset value for slots in cardboard is between 0.35mm - 0.45mm, depending on your joint fit preferences.

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