Week 3 – Computer Controlled Cutting

Fab Academy – Week 3

Date range: 2nd Feb - 10th Feb

Instructor: Daniele Ingrassia and Debabra Goswami

🧠 Learning Objectives

• Demonstrate and describe parametric 2D modelling processes.
• Identify and explain processes involved in using the laser cutter.
• Develop, evaluate and construct a parametric construction kit.
• Identify and explain processes involved in using the vinyl cutter.

📋 Assignments

Individual Assignment

• [ ] Design, laser cut, and document a parametric construction kit, accounting for the laser cutter kerf.
• [ ] Cut something on the vinyl cutter.

Group Assignment

• [ ] Do your lab's safety training.
• [ ] Characterize your laser cutter's focus, power, speed, rate, kerf, joint clearance and types.
• [ ] Document your work to the group work page and reflect on your individual page what you learned.

🛠️ Tools & Materials

• Software: Onshape (for parametric design), Inkscape (for vinyl design), Cameo Silhouette Studio, and RDWorks.
• Machines: Chinese generic laser cutter, Cameo Vinyl Cutter.
• Materials: 4mm Cardboard, vinyl sticker sheet, IKEA pendant lamp fitting, LED low watt light bulb
• Tools: Notion AI tool to improve writing

👥 Group Assignment

The objective of the group assignment was to understand the safe operation of the laser cutter and to characterize how different power and speed settings affect cutting results, including measuring the kerf of the machine.

Safety

Before operating the laser cutter, our local instructor guided us through a few safety rules for operating the laser cutter, including:

• Never leaving the laser cutter unattended while operating
• Ensuring proper ventilation and exhaust is on
• Keeping flammable materials monitored at all times
• Knowing the location of the fire extinguisher and emergency stop

Fire extinguisher near the laser cutter

Power and Speed Testing

We tested multiple combinations of power and speed on cardboard to observe:

• Whether the material was fully cut through
• Edge quality (burning, charring, or incomplete cuts)

Test boxes to test different speeds and powers.

We started at 100mm/s speed and 20% power and for each box we increased the power and decreased the speed, we found out that 4mm cardboard on a 55Watt laser cutter is best cut at 70mm/s speed and 75% power

Types of fit to design:

Depending on the joint you are designing, different types of fit can be used to control how parts assemble and interact:

• Press / Interference fit: parts are forced together and hold by friction → account for negative clearance (usually –0.1 to –0.3 mm, depending on material and kerf).
• Slip / Clearance fit: parts slide together easily → account for positive clearance (usually +0.1 to +0.3 mm).
• Transition fit: can be tight or loose depending on tolerance → account for near-zero clearance (around 0 to ±0.05 mm).

Kerf Measurement

Kerf is the width of material removed by the cutting tool (such as a laser cutter or CNC router), which must be accounted for in design to ensure accurate dimensions and proper joints. Kerf directly affects the type of fit because it changes the actual size of the cut parts, so kerf must be compensated for in the design to achieve the intended fit.

You can see the gap between the two parts as a result of the kerf size

To measure the kerf, we:

1. Drew a test 30mmx30mm square.
2. Cut the square using the laser cutter
3. Measured the total width of the cut piece subtracted from 30mm and divided by two to calculate the kerf

This kerf value was later used in the parametric design to ensure a proper press-fit for the lampshade connectors.

The kerf test must be done for every machine and with every material you’re going to use.

It was a 30mm square.

0.1 + 0.2 total kerf is 0.3 divided by 2 = .15 which will be updated to the kerf variable in Onshape

🧪 Process & Workflow (individual Assignment)

I think it’s fair to say by now that I am huge fan of lights and lamps 😉 . For the individual assignment, I designed a parametric lampshade kit using Onshape. The goal was to create a design that could easily adapt to different materials and configurations by changing parameters instead of redesigning the whole model.

Step 1 – Parametric lampshade Design

I designed the lampshade with the following parameters:

I sketched a lower holder, upper holder and a panel using these variables.

Step 2 – lampshade Fabrication and Assembly

• Material used: 4 mm cardboard
• Initial configuration: 10 panels

I cut the first version with 10 panels slots on the upper and lower holders. It was fully cut and assembled to test fit and appearance.

After assembling the first version, I decided the lampshade would look better with more panels. Instead of redesigning the model, I:

• Changed the number of panels parameter in Onshape
• Cut only a new top and bottom holder and 5 additional panels

This demonstrated the advantage of using a parametric design.

• I used an IKEA pendant lamp fitting
• Because the lampshade is made of cardboard, I used an LED bulb with very low wattage to minimize heat and reduce fire risk

Step 3 – Vinyl Cutting

I’m kind of known in my makerspace for repurposing cardboard, I’ve made a lot of projects out of it, and most of them are lampshades 😄 So it felt only fitting to design and cut a lampshade sticker for this assignment.

To create the sticker design, I started from an image of the lampshade I took earlier. I:

1. Used ChatGPT to generate a black-and-white silhouette of the lampshade: with the following prompt: "Take this image of a lampshade and convert it into a clean, black-and-white silhouette suitable for making a vinyl sticker. The output should clearly show the outline and main shape of the lampshade with no shading or colors, emphasizing simple, solid areas that can be easily traced into vectors.”

Original picture of an old lampshade I made

1. Imported the silhouette into Inkscape
2. Used the Trace Bitmap tool to convert the image into vector paths

1. Cleaned up the vectors and made minor design adjustments
2. Exported the final design as a DXF file for cutting

Vinyl Cutting

The DXF file was imported into the cutter software, and the design was cut using standard vinyl cutting settings.

After cutting, I used the sticker on my vinyl cutter.

⚠️ Problems & Solutions

• Slight inconsistencies in cardboard thickness and bends affected results. I had to find a level of laser focus that can cut without burning or charring the cardboard.

📊 Results

• Vinyl sticker
• Lampshade

🧩 Files

• Onshape file
• Inkskape sticker in svg

📝 Reflection

• Designing parametrically in Onshape allowed me to iterate quickly without starting over, which is especially useful in digital fabrication. Next, for this assignment, I plan to fully define the Onshape lampshade file with variables so it can generate a wider range of shapes and sizes.