Design choices — system housing

The system housing is the structure that hold our extrusion subsystem together. It must meet these requirements:

System housing holding the barrel and motor

1. Hold the motor and barrel at appropriate height
2. Constrain rotational and linear motion of the barrel
3. Constrain rotational and linear motion of the barrel
4. Withstand high temperature thermal stress
5. Able to be manufactured and assembled quickly

To meet these requirements, we to use ¼” laser cut mdf as our material of choice.

1

Mdf and laser cutters allow us to cut at whatever planar locations we desire. This means that properly lining up the barrel and motor is easily achieved with 2 or 3 trials.

2

To constrain rotational motion of the barrel, we set a 6–32 screw inside the barrel. To constrain linear motion of the barrel, we use 4 4–40 screws to attach a plate on the other side of the 6–32 screw, as this is the only direction the barrel can linearly translate.

Barrel and System Housing: A screw prevents the barrel from rotating.

3

To constrain rotational motion of the motor, we connect 4 connectors to the base plate with 4–40 screws and T-Slot Joints. Then, we run two 8–32 screws through the motor. The 4 connectors also constrain linear motion of the motor.

Motor and System Housing: We secure the motor to prevent it from twisting.

4

In terms of thermal stress, the ignition point of mdf is around 220 degrees Celsius. Although we are heating the PLA around this temperature, the mdf will only receive a fraction of that heat meaning that mdf is a reasonable choice for our system housing.

5

Because the entire system housing is assembled using T-Slot Joints, it can be assembled in around 10 minutes. It is also manufactured in around 7 minutes with a 60 watt laser cutter.