Week 3 Assignments - Computer Controlled Cutting

Laser Cutter Safety

Parametric Construction Kit Design

Press-Fit Construction

Octopus Vinyl Sticker

Group Assignment - Laser Cutters

For the group assignment, we went over the lab safety traning for laser cutting and worked through characterizing aspects of lab laser cutters. More details are on the group assignments page.

Epilog Helix Laser Cutter

In addition to the primary laser cutters in the Super Fab Lab, some earlier model laser cutters are available for use. I also reviewed characteristics for the Epilog Helix laser cutter.

Safety

I reviewed laser safety with staff for the Epilog Helix. This included details about materials, operation, monitoring, and fire safety.

Laser Cutter Details

Power

This Epilog Helix is a 75 Watt laser cutter.

Focus

Focus for the Epilog Helix is a manual operation using a manual focus gauge. The gauge attaches to the laser head. Focus is optimized by adjusting the bed of the laser to the point of the focus gauge.

Settings

For the Epilog Helix laser cutter, I reviewed the settings across different material. Epilog provides primary documentation for Epilog laser cutter settings across different materials. Specific documentation is available for Epilog Helix material settings.

This includes recommended settings per material type for:

• Raster Engraving - DPI, speed, and power
• Vector Cutting - Frequency, speed, and power

In addition a lab reference is available that includes some setting refinements based on available materials.

Kerf

To measure kerf on the Epilog Helix, a pattern of 10 rectangles was designed and cut with the Helix. The pattern was created as an Autodesk Fusion sketch, which was exported as DXF and opened in Adobe Illustrator as part of the laser cutting workflow.

The pattern was cut with the Helix using settings for cardboard.

Measurements were taken for the resulting opening for width and height.

Measurements were also taken of the cut pieces for width (all 10 pieces together) and height (2 pieces at a time).

Calculations were made for the kerf, based on the specified and measured dimensions. Outline height and width, as well as average piece height, were the direct difference. The overall width of all pieces was the difference divided by the number of pieces. An additional calculation of (outline - piece) / # cuts for width and height was made.

Aspect	Specified (mm)	Measured (mm)	Kerf (mm)
Outline Height	30	30.25	0.25
Outline Width	150	150.30	0.30
x10 Piece Width	150	147.84	0.22
x10 Piece Avg Height	30	29.74	0.26
Calc Width			0.22
Calc Height			0.25
Overall Average			0.25

The overall average of 0.25 mm was taken as the kerf for the Helix.

Parametric Construction Kit

For the parametric construction kit, I first explored some different kits that had been done previously. Pictures that I saw from Brent Richardson reminded me of the Lincoln Logs toy construction kits (and indeed that was the idea for that design). Of the different examples I saw, that resonated with me for the nostalgia. So, I went about creating my own parametric log-style construction kit from scratch.

Tools

For the parametric construction kit, I browsed through a number of the tools in the listing. I gave more detailed consideration to Inkscape, Fusion, and Cuttle. Each of the tools has some advantages, but also some pretty big flaws for 2D parametric design. Inkscape does not provide parametric capabilities as such. There is the clone tool that gets toward it, but is not really parametric and seems to be excluded from the assignment. Fusion sketches provide sketch constraints but do not seem to support 2D operations for things like boolean combination or incremental changes in patterns. Cuttle does not provide constraints, but does allow for coding constraints through expressions. After some exploration in each tool, I selected Cuttle for the parametric design.

Design

I decided to model the connecting notch first and then log pieces that would use the notch as primary connection.

Parameters

The main parameters in the model were for:

• thickness (3.75mm) - thickness of the material (this drives the size of the notch). available cardboard stock was a bit of a mishmash, so an average measured value across multiple pieces was used.
• kerf (.26 mm) - width of material removed by the laser (this also drives the size of the notch for close fit). the average measured value for the laser was used.
• height (30mm) - common height of basic components. this height seemed reasonable to allow for top and bottom notches while still being somewhat log like.
• unitwidth (35mm) - components come in size multiples of 1 to 4, this is the width of the basic unit. this width seemed reasonable to allow for enough material around the notch while still being somewhat log like.
• size - for a given component, how many units wide is it.

Notch

The notch was modeled as a rectangle for the main area, with a trapezoid shape to define the chamfering at the entry point. Specific parameters for the notch were:

• width - in order to get a close fit for the thickness of the material in the notch opening, notch width is the basic thickness accounting for kerf (half on each side): thickness - kerf
• height - height is one quarter of the overall height of the basic height: height / 4

Piece

The base piece was modeled as a rounded rectangle, which was parameterized as follows:

• The size of the piece determines how many notches are present. Each notch is in the center of a piece of unit width. If there is more than one notch, there is an additional full unit of width between the notch pieces. So, the overall width of a given piece is: unitwidth*(2*size-1).
• Notches are placed using 2 levels of repetition. The base notch is centered at the top of a unit segment and then mirrored to the bottom. The top/bottom notch is then linearly repeated across from the left side of the piece, with size number of repetitions every 2 * unitwidth.
• With the base piece and notches created, a boolen difference is used to create the final parametric piece.

Press-Fit Construction Kit

The press-fit construction kit was created using the parametric base design. Four different types of part were created using different parameterized sizes (1, 2, 3, 4).

The base parts were exported as an SVG from Cuttle as a template. The template was imported into Illustrator as part of the laser cutting workflow. An initial laser cut was done in cardboard for the basic parts to test the fit. The fit seemed to be good based on the design. Multiple parts of each size were copied and oriented to create a multi-part design as a basis for the kit. This was cut multiple times to produce the pieces for the kit.

The kit was tested by creating a basic cabin structure. This held together well with only press-fit. An extension to the kit would be to model roof / chimney parts to fith with the types of content available in the origial Linconln Logs kits.

Vinyl Cutter

Options for vinyl cutting tools included Roland and Silhouette. I chose to use the Silhouette cutter to create a vinyl sticker.

Design

I selected a basic octopus design as an image. The process used was:

• Imported image into the Silhouette Studio software.
• Used the trace outline feature to create the cutting path.

Cutting and Finishing

For creating the sticker, the following steps were taken:

• Set up the vinyl with the cutting mat and launched the cut.
• Weeded the cut vinyl sticker.

I did some trials, both basic shapes and the final shape, in order to make sure that the cutter was working. Initial tests had some errors in cutting. The cutting mat was older and had lower adhesion, and the testing vinyl had some wrinkles. With a new cutting mat and smooth vinyl the cut came out well.

Design Files

For the week's activities, following are the main design files.

• Octopus Sticker Design (Silhouette Studio Project)
• Parametric Construction Kit Template (SVG - Cuttle)