Planning
The majority of the design work was done using the website makercase.com. This website allowed me to specify box dimensions, material thickness, and the width of individual finger joints.
The box edges were set to be 4 inches, and the board thickness was measured to be 0.189 inches. The width of the finger is directly correlated to how many of them can fit along one edge. I settled on 0.637875 inches; this is the maximum width to have 3 full-size fingers along each edge. This way, the product will have the signature box joint look while fingers are still wide enough to retain their strength.
Box dimensions and specifications
The final step before downloading the vector file and importing it into Adobe Illustrator was to establish the kerf of the laser cutter. I used the Epilog Fusion Pro to cut out 10 rectangles (11 longitudinal cuts), pushed them all to one side, and measured the resulting gap. The kerf was calculated to be 0.006 inches.
Caliper reading for kerf test measurement
Based on this kerf value, I cut out two edges of the box to test the press fit. At 0.006 inches, the finger joint does hold together but not strongly enough. It only takes a few pushes to disconnect the joints. So, I increased the kerf size to 0.007 inches to better compensate for the material lost during laser cutting. The resulting joint requires considerable force to pull apart.
Test finger joint snapped together. Kerf = 0.007 inches.
Final Laser Cutting and Assembly
The SVG file generated using makercase.com was imported into Adobe Illustrator, where I added my name, course information, and college crest. The laser cutter settings are as follows:
For vector cut:
- Speed: 22.5%
- Power:100%
- Frequency:10%
For engrave:
- Resolution: 600 DPI
- Speed: 100%
- Power:50%
These settings were based on the reference manual for the Epilog Fusion Pro.
Sides of the box all laid out
The box was relatively easy to assemble; the fingers fit snugly together. It takes a bit more effort to attach the top and bottom panels because pressure needs to be applied evenly along all four sides to push the fingers into place.
Clean workspace when finished
Cost Analysis
There are three main types of costs to this project: material, labor and personnel, equipment and facility.
| Cost Type | Cost | Price | Source | Quantity | Total |
| Material | 2’x2’x1/5” Plywood | $7.28 | Home Depot | 9/32 | 2.0475 |
| Labor | Laser Cutter Operator | $19 /hour | ZipRecruiter | 2 | 38 |
| Prototyping Engineer | $36 /hour | ZipRecruiter | 1 | 36 | |
| Quality Control Engineer | $37 /hour | ZipRecruiter | 0.2 | 7.4 | |
| Overhead | Facility Cost (Machine Time) | $12.73 /hour | TechGen | 1.25 | 15.9125 |
| Total | 99.36 |
