3. Computer-Controlled Cutting

This week I learnt how to use the laser cutter, and how to use it to create a Press-fit construction kit.

Assignments for this week (Feb 5 - Feb 11):

Group assignment:
- Do the safety training for the lab’s lasercutter
- Characterise lab’s lasercutter’s focus, power, speed, rate, kerf, joint clearance and types
- Document work

Individual assignments:
- Create a Press-fit construction kit, which can be assembled in multiple ways
* Account for the lasercutter kerf
* For extra credit, include something that’s not flat
- Cut something on the vinyl cutter

Group Assignment

For this week’s group assignment, we had to figure out our lasercutter’s focus, power, speed, rate, kerf, and joint clearance.
Group documentation here

About the 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

Some of my personal learnings

How FabLab Kamakura's Laser-cutter works

It's a type of cutter that utilizes a CO2 tube, which generates a laser beam through the electrical stimulation of a gas mixture predominantly composed of carbon dioxide.
A series of mirrors and a focusing lens precisely guide and focus this beam onto the material's surface, enabling intricate cutting, engraving, or marking through the processes of melting, burning, or vaporizing the material.
(Reference: https://fabacademy.org/2024/labs/puebla/students/ximena-mendieta/assignments/week03.html)

What materials can be cut using laser-cutters?

Depends on the type of machine. They typically cut Wood, acrylic, fabric, paper, leather, glass, certain plastics, rubber, etc.
CO2 lasers cannot cut metals as their lasers operate at 10 micron but there are some more sophisticated machines such as Plasma, water-jet, etc.

What's a Press fit Construction?

It's a method of joining two components together by applying pressure to fit one part slightly larger than the other into a hole or fitting, creating a tight connection solely through friction without the need for additional fasteners.
(Reference: https://fabacademy.org/2018/docs/FabAcademy-Tutorials/week3_computer_controlled_cutting/press_fit.html)

What is a kerf?

- It's the small width of material removed by the laser beam during the cutting process. They are typically around 0.3-0.5 mm
- It's important to account for kerf width, as it can affect the fit of the final design, especially for Press-fit construction. 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.
(Reference: https://making.stanford.edu/resources/)

What's a Parameric Design?

It's a design method that uses algorithmic approach to creating structures.
Benefits of parametric design includes; allowing for design modification with accuracy and efficiency, reducing time to market, enabling complex forms.
(Reference: https://www.sciencedirect.com/topics/engineering/)

The Press-fit construction concept reminded me of a traditional Japanese carpentry technique called “Kumi-ki (組木)” which I’m a big fan of.

It’s a joinery technique where wood pieces are interlocked together without needing nails or fasteners to form very stable 3D objects. I love its intricate and clean aesthetics, and low environmental foot print. I was hoping to incorporate this concept into my personal assignment, but didn’t really manage it due to time constraints.

Personal assignment - Press-fit construction kit

For this week’s assignment, I set on a challenge of creating a rack whose size can adjust to fit to a wide range of owners’ needs.

Design (1st design)

While scanning for design ideas, I found this simple shelf that I thought I can adapt into a modular design.
Source: Creema

I first used scissors to make a simple prototype to test out a design, and then sketched it out with rough measurements.

For the actual Press-fit modelling, I decided to get more practice using Fusion 360 (which was another challenge in itself) and eventually I completed it.

I found the process of parametric design quite tricky, especially while considering my own requirements such as fitting in the narrow space of 7.7cm behind my stoves, ensuting rack size appropriate for spice bottles, overall cadboard size of 30 x 60cm, etc.
To make the structure more stable, I was planning to make the joint into snap-fit, but my instructor Rico told me it wouldn’t work on cardboard. I tested-cut it anyway and he was right!

Below are the parameters I set for my design.
Based on the groupwork results, the the best press fit for our 3mm thick cardboard was 2.55mm, thus the offset value for the kerf was .225mm.

Below you can see how I set the slot width to be Material thickness - kerf.
This way, if I change the dimensions such as the material’s thickness, Fusion 360 will automatically reflect the measurements without me having to manually change them.

Design (2nd design)

After sharing the 1st prototype with my Instructor Rico, he shared with me a design of Chinese display cabinets, which inspired me to make another design.

It’s essentially a series of boxes that can be stacked together. This is the side-view draft sketch I made on Excel.

For the base box, I was inspired by Lucas Lim’s box design.
I adapted it a little by making the joints resemble a plum flower (another good exercise in parametric design).

I was also interested in incorporating a Kumiki-like aesthetic to the design, and adding a back flap controlled by a living hinge, but I ran out of time. This is a rough prototype I quickly tried out (still lots of room for improvement).

Cutting and Assembly

I exported the final Press-fit designs into .DXF files for laser-cutting.
The steps for operating the laser-cutter are documented over in the groupwork page.

Here is the final result!

I expected the cardboard structure to be quite flimsy but it was surprisingly quite sturdy. Maybe one day it might come in handy as a prototyping technique.

Vinyl cutting

There are 2 models of vinyl cutters at FabLab Kamakura.
- Silhouette Cameo
- Brother ScanNCutDX

I used the Brother vinyl cutter to cut out a cute duck sticker for my coffee mug. I simply loaded a duck shape I liked for cutting, set the sticker sheet on the base sheet, and cut it.

Tutorial

Design files:

Final Fusion360 files

Links

https://fabacademy.org/2019/docs/FabAcademy-Tutorials/week03_computer_controlled_cutting/press_fit.html

Reflections:

This was another week packed with learnings, including…
- Slightly better understanding of how to navigate Fusion 360
- How to model 2D designs parametrically
- How to think in 3D through rough prototyping and sketching
- How to cut using the laser cutter and vinyl cutter

Some of my main learnings
- For some reason, my parametric parts designed on Fusion 360 had 2 overlapping lines. We had to stop the printer mid-way as the machine was going over lines which were already cut. I could not figure out when or how they were made, but I hope to be more careful next time.
- I personally found parametric modeling and thinking in 3D objects to be very challenging. It was especially so since my design had quite a few specific requirements (such as overall depth and height, material width, etc). I also learnt that parametric modelling in Fusion 360 is tricky because it doesn’t allow the user to keep the parameter window out while designing at the same time. I am curious to know if FreeCAD might be easier in that respect.
Since I found it much easier to think on paper than on the software, next time I will sketch out the exact measurements before starting designs on the PC.

Further Questions:
I am curious to explore more into what kind of designs/functions Parametric design can enable (that I still haven’t explored)
I am also interested in exploring the living hinge and how it can be applied to woodcrafts.

Assignment Checklist:

• [x] Linked to the group assignment page
• [x] Explained how I created my parametric design
• [x] Documented how I made my press-fit construction kit
• [x] Documented how I made something with the vinyl cutter
• [x] Included my original design files
• [x] Included hero shots of my results