3. Computer Controlled Cutting - STUDENTS

Terms and Definitions (Oliver)

Focus/Focal Point - The point where the laser beam converges to its smallest diameter and highest energy density. The focal length is a fixed property of the focusing lens. The focus distance is the adjustable height between the lens and material surface, which should be set so the focal point occurs at or slightly into the material for optimal cutting.

Power - The energy output of the laser beam, expressed as a percentage of the machine’s maximum wattage capacity. Higher power settings deliver more energy to the material, enabling cuts through thicker materials or faster processing speeds.

Speed - The travel rate of the laser head across the material surface, typically measured in mm/s, inches/min, or m/min. Lower speeds allow more energy transfer per unit area, resulting in deeper cuts or more thorough engraving. Speed is inversely proportional to the exposure time any given point receives.

Kerf - The width of material removed by the laser beam during cutting, typically 0.1-0.5mm depending on beam diameter, focal point, power, speed, and material properties. Kerf must be accounted for in design files to achieve dimensionally accurate parts.

Joint Clearance/Types - The intentional gap or tolerance between mating parts in an assembly. Proper joint clearance accounts for kerf width, material thickness variation, and char/melt characteristics to ensure parts fit together as intended. Common laser-cut joint types include finger joints, box joints, press-fits, tab-and-slot connections, and living hinges.

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Focus Test (McKinnon)

A laser cutter’s focus is the distance between the lens and the material. Many laser cutters like the Epilog laser cutters in the Charlotte Latin Fab Lab have auto focus. This allows the laser to find the correct focus point for the best result while cutting. For the focus test, we called this point 0.

Design Process

The file was designed for testing laser cutter focus. A Fab Academy logo PNG was downloaded from the internet and imported into CorelDRAW. The logo’s bitmap was traced. Neither hairline nor 0.5pt were selected because there was no need for cutting edges of the logo.

The image was then copied and pasted 5 times vertically. Each one of these logos would be given a different focus. The top logo would be given a focus of 0 and from there on, each logo’s focus decreases by 0.05.

Focus Control

The focus was controlled through the laser cutter’s focus menu. The joystick raises and lowers the bed precisely, allowing the user to adjust focus even while a job is being run.

Results

The top logo, with a focus of 0, is the darkest. It was closest to the laser and the most energy was applied to it. As each logo goes down, the darkness decreases as the laser got further and further from the material, so less energy was being applied to each logo.

Link to design file

corel_focus_file

(The file was changed from a .cdr file to a .svg file )

Clearance Test

The clearance test determines the optimal gap size between interlocking parts to ensure a proper fit.

Process

We created a test file in CorelDRAW with multiple rectangular slots of varying widths and a test square piece.

The design was cut on the big laser cutter.

Results

We tested the square piece in each gap to find which clearance provided the best fit. The 0.15” gap fit the best - tight enough to hold securely but loose enough to assemble easily.

Interestingly, when we measured the test square with calipers, it measured exactly 0.15”, confirming our laser’s kerf matched our design expectations.

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Kerf Test (Max)

The kerf test measures how much material the laser beam removes during cutting. This is critical for designing parts that fit together accurately.

Test Setup

We designed a simple 1.00” × 1.00” square in CorelDRAW to test on cardboard material.

Cutting Process

The square was vector cut on the big laser using our standard cardboard settings.

Measurement and Calculation

After cutting, we measured the actual square with digital calipers.

Measured size: 0.98”

Calculation:

• Original design: 1.00”
• Actual cut size: 0.98”
• Total material removed: 1.00” - 0.98” = 0.02”
• Kerf per side: 0.02” ÷ 2 = 0.01”

Result: Kerf = 0.01” (0.01” removed from each side of the cut line)

This means when designing parts that need to fit together, we need to account for 0.01” of material removal on each cut edge.

Detailed workflow documentation: Google Doc

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Joint Types (Max)

For this assignment, we explored various joint types commonly used in laser cutting to create 3D shapes from 2D materials.

Common Laser-Cut Joint Types

Tab and Slot: Tabs fit into matching slots; simple and widely used.

Press-Fit (Friction Fit): Slightly tight tabs create friction so parts stay together without glue.

Finger Joint (Box Joint): Interlocking rectangular “fingers” increase strength at corners.

T-Slot Joint: A tab slides into a T-shaped slot and locks in place; good for structures.

Mortise and Tenon: A rectangular tenon inserts into a mortise hole; very strong and traditional.

Cross-Lap Joint: Two pieces intersect with notches so they sit flush.

Dovetail Joint: Angled tabs prevent pieces from pulling apart; strong but more advanced.

Living Hinge: Repeated cut patterns allow rigid material to bend.

Snap-Fit Joint: Flexible hooks or clips “snap” into place for tool-free assembly.

Puzzle Joint: Pieces connect like puzzle parts; often used for decorative or modular designs.

Max’s Native Files .zip

References

• Fab Academy Charlotte 2024 - Week 3B
• Fab Academy Charlotte 2025 - Week 4
• Fab Academy 2026 - Computer Cutting Class Files

Workflow

1. Downloaded the joint template file (joint.fcstd) from the Fab Academy computer cutting class files
2. Opened in FreeCAD - The file format (.fcstd) is exclusive to FreeCAD software

1. Exported as STL - Converted the 3D file to STL format for compatibility
2. Imported into Fusion 360 - Opened the STL file in Fusion 360
3. Created 2D profiles - Projected the 3D pieces onto a flat plane to create 2D cutting profiles
4. Broke projection links - Disconnected the 2D sketches from the 3D bodies to edit them independently
5. Duplicated missing joints - Some joint types didn’t have matching pairs, so we duplicated them

1. Exported as DXF - Saved the 2D profiles as a DXF file (standard laser cutting format)
2. Transferred to laser computer - Placed the file (joints.dxf) in the shared Google Drive
3. Cut on the Epilog laser - Opened the file on the laser cutter’s computer and cut using our established workflow

These joint types are commonly used in laser cutting to create 3D structures from flat sheet materials, enabling complex assemblies without the need for fasteners or adhesives.

Speed, Power, and Frequency Test

To test these settings, we decided to create a 10 x 3 grid of small (0.5” x 0.5”) squares, with each column representing one of the three settings and each row representing an amount/level (percentage) of the settings. This was done by Yian Hu in CorelDRAW, and was roughly inspired by Elle Hahn, Amalia Bordoloi, Andrew Puky, and Jenna Chebaro’s group project documentation.

While designing this test, it was important to ensure that each square was unique so that it could have its own settings in the Epilog Fusion software. To do this, the outline of each square was changed to a different color with the CorelDRAW color palette. Each column had a rainbow-like sequence to allow for differentiation when working in the Epilog software.

Here is the native file of my design:

Corel Draw Test Design

It should also be noted that every line in this design was hairline, as everything was to be cut entirely instead of engraved.

After the design was completed, it was then uploaded to the Epilog software to prepare for testing. First, each square color was separated into a unique object by clicking “Color” next to “Split By:” in the object tab. This formed a total of 30 individual identities. Then, starting at the first row of squares, the speed, power, and frequency settings were increased in increments of 10% per row. This meant that the first (speed) column would be 10% speed for the first square, 20% for the second, 30% for the third, and so forth. The same can be said about the power and frequency columns. To ensure consistency in test results, the two settings that were not tested in a column were kept at 100%. For example, in the speed test column, power and frequency were at 100% no matter the square. Here is what the design looked like after configuring each setting correctly.

Once the design was ready for testing, it was sent to the Epilog Fusion laser cutter by clicking “print” in the software. Before running the test, the laser was homed (returned to the original position) and then focused by using the auto-focus button on the laser cutter. To start the cut, the design was selected in the laser cutter menu and then the start button was pressed.

Here is what the completed test looked like after the cut was complete.

As can be seen, the quality of each square varies significantly as the setting percentage changes. When speed is lowered, the laser spends much more time on each point, meaning that more power is devoted and the cuts are much deeper/thicker. When power is lowered, the laser cannot fully cut through the material which causes very light and shallow lines. Since frequency does not make any significant impacts on cardboard, there are little to no differences between each square in the frequency column.

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Last update: February 18, 2026