Jasmin Cheng

Assignment

Make something big.

My Goals

• Make a pressfit bachelor chair

What I Learned

• How to design furniture
• How to make paper prototypes
• How to create test joints on the Shopbot
• How to use the Shopbot
• How to use sand paper, a chisel and the Japanese saw

What I want to keep working on

• Add table top and folding functionality to pressfit bachelor chair design
• How to use the Shopbot for 3D milling

Tooling, Materials & Speeds

• Shopbot
• 12.5 mm plywood (12 m x 24 m)
• 3mm mill bit for down cut, 6 mm for up cut
• Speed Rate: 12000, Feed Rate: 25mm/sec, Plunge Rate: 20mm/sec

Downloads

The Candido Pressfit Step-Stool (Illustrator and DWG)

Documentation

This week’s assignment was probably the most creative assignment of the Fab Academy program (except maybe for Laser Cutting). Basically, all we had to do was make something big using the Shopbot and a sheet of 12m x 24m plywood.

Concept Sketching & Paper Prototyping

Before using the Shopbot, I spent some time making paper prototypes of my ideas. It came down to 2 ideas - a lotus shaped meditation platform, or the bachelor chair - a chair that folds into a ladder and a table.

I decided to to make the bachelor chair. I didn’t have any previous furniture designing or building experience, but I was fascinated with the mechanics of the chair, and felt like the press fit aesthetic would make this old-fashioned piece more modern.

I made numerous sketches of the chair to wrap my head around the mechanics. I also took measurements of the bachelor chair at Fab Lab Wellington, which I would use as a starting point for my design.

Furniture Design in Illustrator

Once I had all the measurements, I went into Photoshop to design the parts. Despite having measurements to start with, there were aspects of the design of the bachelor chair that had to be re-considered because it will be cut out of plywood, not solid wood.

I was faced with 3 big design challenges:

• Base legs of the bachelor chair all came up into the seat at an angle, making it (almost) impossible to design a press fit seat
• Ladder steps had to be reinforced because the load would be coming down the vertical length of the plywood, rather than from the surface
• Mechanics of how the table top would swing around from one position to another to create the various stages of the bachelor chair/ladder/table were complicated to wrap my head around

My first attempt to solve all these challenges led to something that resembles more of a torture device than a bachelor chair. Wendy and Stu encouraged me to model it so I would be able to see how it would actually work.

It was actually scarier as a model than as a blueprint. With the model, it was easy for Wendy to point out how unstable a square/rectangle structure would be, which seemed to make sense in 2D, but made very little sense in 3D. We also decided that because of the complexity of the bachelor chair mechanics, we would focus only on the base of the chair, which would be a chair on one side, and a step ladder on the other side.

The new model was clearly more stable with nice proportions. The press-fit aesthetic suited this chair/ladder, making it look modern and functional and approachable, which was what I wanted.

I showed this design to other students, and the feedback that I got from Anna and Ted were on how the foot stool and the steps of the ladder tilted in at an 18* angle, rather than 90* angle from the ground. I refined my measurements in Illustrator and felt confident that after 2 models, I was ready to cut out the design on the Shopbot.

Shopbot Production

Anna and I worked on a joint test together. We were really surprised at the results - we were expecting a tolerance difference of 0.1 or 0.2 mm (like we saw with the laser cutter), but the best fit was actually at 0.5 mm. Prepping the joint test was good practice for cutting the actual assignments.

For this design, I decided on the following settings:

• 6mm drill bit
• 2 passes up
• 1 pass down

How to set-up PartWorks file:

• Export your Illustrator file as an DWG
• Open the DWG in Partowrks
• Set-up the size of the bed (2400 mm x 1200 mm)
• Join all unjoined objects - it’s really important that all points are joined because otherwise, Shopbot can’t tell which is the inside and which is the outside of the object
• Dogbone and T-bone - always do this at the beginning! If you wait til the end and realize that some of your joints won’t dog bone, you’ll have to fix your file and re-start the process all over again and that’s not fun at all.
Create layers - you want to create layers for each type of cut. Typical layers I use are: “Screws”, “Outside Cut”, “Inside Cut”. Once you’ve created a layer, move those objects to that layer and lock it.
• Create tool paths for each layer by highlighting the objects that go together - profile for shapes, drilling for screws
• Select the kind of screw that you’re using (6 mm or 3 mm)
• Set cut depths - 2-3 mm for screws, 12.5-12.7 mm for cutting through
• Pecking is for drilling holes
• Select “inside” or “outside” based on where you are willing to lose material - you may need to tweak your designs when you can see how the tool path eats away at the material
• Save tool paths by grouping together the tool paths that use the same drill bit (i.e. "Down 3mm” or “Up 6mm”)

Craig gave us good advice on how to set cut-depth for UP and Down cuts:

• Start with the Down cut
• Down cut should be the shallowest (i.e. 3.5 mm)
• Up cut should be the deepest, but it needs to start where the down cut ends (i.e. start depth at 3.5 mm, cut depth at 9.2 mm - adding up to 12.7 mm)

How to use the Shopbot

• Put the material on the machine and clamp it down
• Turn on Shopbot machine and open Shopbot application
• Move the drill-bit to the place you want to set the Z axis somewhere in the middle of the board using the keyboard (make sure keyboard is aligned in the same direction as the board) by opening the yellow window (make sure to close the yellow window once you’re done moving the Shopbot arm)
• Change the drill bit by loosening the extraction skirt and using the tools to loosen the collet (make sure the spindle is off)
• Insert the drill bit allowing for half a cm of the shaft showing and tighten with tools
• Test the z axis by going to Cuts>C2 and zero the z axis by using the metal plate (make sure metal plate makes contact with the bit
• Set the x-y axis by going to Cuts>C1, sending the bit to the desired origin
• Turn on extraction and turn on the spindle
• Click Cut and select the cut file you created in Partworks (make sure you’re cutting the right file with the same drill bit)
• Stand close to a Stop button and watch the Shopbot closely - stopping the machine if the drill is at risk of hitting a screw or a clamp - when you stop the Shopbot (with the stop button or space bar), you can resume the cut job)
• When the cut job is finished, turn off extraction and the spindle



Wendy helped me a lot with this because there were quite a number of screw holes - both on and off the object, and I was unsure which ones to use. To speed up my process (as there were many undergrads waiting to use the machine), she showed me that I could start unscrewing the board, and pulling off parts while the Shopbot was on its final pass (while obviously paying attention to the Shopbot at all times, and being prepared to press the Stop button if the machine came too close to me.



Stu helped me put the chair together using a mallet, a Japanese saw, a hammer, a chisel and some screws. It’s a proper press fit design. Unfortunately, I hadn’t taken dog bones into my design and the steps were just off. Also, I can’t use the chair as a step ladder as I originally hoped because the ladder tips over. But I’m happy with this as a first prototype and believe this is a good starting point for the bachelor chair.





Downloads

You can download the DWG file here.