Concept 1 is based off this project http://www.reprap.org/wiki/Web4deb and parts from McMastercarr. This method uses a wood auger to work the plastic. There is a heated chamber that will melt the plastic and force it through an opening. Mixing the plastic might require a longer heated zone, so that the screw can mix the molten plastic longer. To melt the plastic, the hot chamber is heated using Ni Chrome wire and has multiple heated zones to endure the plastic is at the proper temperature. Some issues with the design is a wood auger is not designed to perform like a injection mold auger. In an ejection mold machine, the auger has multiple zones. The first halve moves the material with constant groves depth, next it is compressed as the groves get smaller, and finally it is pushed to the end with constant grove dept.
Concept 2 is based off a melt flow index machine. It cost just about the same just is easier to build and less parts. It will use a weighted plate to provide constant pressure to give a constant flow. The heat will be provided by AC heating rods inside the main cylinder. We will need a thermocouple inside to maintain a constant temperature. This build will require minimal electronics, basically a few relays and maybe a motor controller. Normally you would use water to cool down the wire but because it is important to keep out moisture, fans will provide air to do the cooling. The diameter of the wire is thin enough this should cool it. To maintain the 1.75 +-.05 mm, we will need to test out different off the shelf nozzles to see what they produce. In the drawing there is a .17″ nozzle but the inside of it is .12, which is a little larger than 3mm. The wire will shrink a bit and might fall within tolerances. If this does not work we will have to machine a nozzle.
Concept 2 Rev1.1
In considering safety of the system, some changes were made to help protect the user from the 400 degree F pot of molten plastic. The pot has been encased in wood to protect from burns and the pot from moving. The pot is encased in a fiberglass insulation, but is not seen in the drawings.
Concept 2 Rev1.2
A better method to rotate the spool was added. Wooden gears will turn the wooden spool. The goal is to be able to easily change out spools, so one of the spool sides will come off and allow the filament to be easily removed. Also, a heater band was added instead of a heater rod. This will provide more power and better distribution of the heat. The price difference on the heater was not that much different considering we don’t need to drill into the 3″ pipe anymore plus going from 175w to 500w is a plus.
Concept 3 Rev1.0 Plan B
This is a redesign based on a combination of concept 1 and concept 2. A 1″ pipe was selected to reduce price and with the screw on top. A continual feed of plastic pellets can be supplied to the pineapple. The pineapple melts the plastic and mixes it. This design will allow for larger volumes of plastic to be made and also greatly reduce the cost. The overall height was dropped down to 28″. The machines that cut out all the wooden pieces has a max travel range of 30″ (we know because we over extended it and broke it). A box for the electronics was added and taps to help put the device together were added.