CNC Chair Project RD

The goal of this project is to learn the designing and manufacturing process center around a CNC machine. A CNC machine use a type of manufacture called subtraction manufacturing where it remove material from object to get your desired shape. In my case I plan creating a chair from a 4fftx4ft sheet of plywood to learn how to utilize this machine. The particular machine I am using comes from Carbide 3D with a 4ftx4ft bed. I am hoping by taking on this project I can understand both the hardware and software of this machine to manufacture more complex objects and move on to cutting hard materials such as aluminium.

4ftx4ft 3/4in of plywood

Memory foam

Canvas

CNC machine

Fusion 360 Carbide create 3D

We need to define the problem. I have a 4ftx4ft piece of plywood than need to be cut and assemble to a chair/bench. I originally wanted to do a sun chair. However, the area of the wood was to small for a full scale sun chair. So, I decide to swap to a simple artist lounge chair with these criteria in mind: comfortable, lightweight, and relative easy to assemble with instructions.

After analyzing and researching, I gain a general idea of how I want my chair to look and be assemble. I want my chair to be able to be most slotted together and be quickly manufactured for assembly lines. I tried to make the measurements proportional to the size of a standard dining table chair. So with these ideals in mind I begin creating a sketch of my chair in a fully assembled. I then on graph paper, broke down my chair into individual pieces: back, seat, two real legs, and two front legs. I added possible cut outs to the seat and backrest where the legs can be fit in and create more accurate measurements based on the width of my materials.

To try out this design I first create a 1:4 scale model out of cardboard to test the stability of the design and figure out potential weak points. Through this process I Was able to create a more complex model in Fusion 360 which was able to utilize joints in assemble instead of adhesive to bond parts.

I started this process by turning my paper sketch of my chair into a 3D model using fusion 360. Fusion 360 is a online CAD software used by engineers all across the globe to create, analyze, and modify designs before being put intro production. Creating a model of my chair allows me to make rapid adjustments to my chair design and check my tolerances. After creating my model I then use the arrange tool to create a copy of my chair and lay each part on a plane. From here I can use my flatten chair to project each part of my chair into a sketch, which is just a 2d drawing of my chair. I then converted the sketch into a .dxf file(Drawing exchange format) to be able to convert the line into vectors when I imported into carbide create.

Carbide create is a software design by Carbide the creators of the cnc machine I use. This software is a crucial step in the process it tells the machine where to cut, how deep to cut, and how fast it should be moving through the materials. For me I need the machine to know that it is using a 1/8in bit and don't cutting any deeper than 5mm. To achieve this I created a layer and assign the vectors of my chair to it. I now can create a tool path where I can put into the information need about the rotor speed, max depth, and bite type. Know we are done, with the toolpath before we can send it off the machine we need to create tabs to ensure once the parts are most cut they don't bend or jump up before they finish cutting to avoid having to recur damage pieces.

In the previous step, we created and configured our chair and tool paths now it is town to cut. To start off we need to make sure our material is properly cut to size and firmly attached to the bed of CNC machine. For my case, I glued my plywood to a sheet of metal covering in a masking tap then clamped the sheet of metal down. Then zero the rotor to a comer of the plywood. From here I can tell the machine from the software to cut my design from vectors I load up into the computer. The cutting takes around 20 minutes to complete but that is not the end of processing I need to do. I sand down some rough edges to make the part mesh properly with each other and then use a small amount of super glue to permanently bind the parts together to insure security.

The scale down model was a good learning experience but it wasn't perfect. So back into Fusion I go I first start by fixing the areas where parts are supposed to mesh and changes it a slightly larger tolerance. I then work on modifying the pieces so they lock into each rather then lay into a slot. During this process I made sure that slots are slightly wider than the thickness of the plywood sheet which is 3/4in just to make sure they can slot in properly. After fishing my modifications I rearrange the pieces and import them into Carbide create to add tabs and create new tool paths for the full scale model.

When cutting something of this scale it is essential to make sure it is properly secure if the material jumps a whole part can be ruin accruing additional cost. So clamps are a necessity to insure

A straight plywood chair would be uncomfortable so adding some foam padding to the seating pad and adding the addition of canvas to protect the foam for weathering. This require a few staples .