Assignment

The Assignment this week is to propose a final project that integrates the range of units covered, answering a variety of questions.

What will it do?

My project is to build an automated vacuum chamber. This vacuum chamber will degas molds and dehydrate various components, in particular fresh cut wood and food. To dehydrate large pieces of wood, it must hold a relatively tight vacuum for extended periods of time, which can be bad for the pump. To overcome this I intend to develop a circuit with a vacuum sensor that will turn it on and off automatically.

Who's done it before?

Vacuum chambers are actually relatively common industrially and scientifically. The problem is they are either quite small or quite expensive. As far as I'm aware, no one has fabbed a vacuum chamber from cast materials.

What materials and components will be required? Where will they come from and how much will they cost?

1: A vacuum chamber. I will be casting this from Hydro-Stone X with some chopped fiberglass mixed in to improve strength. I also need to make a mold, which will be cut from wood and lined with poster board. I ordered a large quantity of Hydro-Stone X for $49 from plaster.com and a small quantity of chopped fiberglass for ~$10 from Amazon.com

2: A lid for the vacuum chamber. I have already made this from burlap and epoxy in a thick composite layup. We already had the burlap and epoxy in the lab, from the Fab Lab inventory. The total value of these materials is ~$5

3: A gasket for sealing the lid and chamber. I have already made this from Smooth-Sil 940, a platinum-cure and food stable silicone which should be durable. I also will use high-vacuum grease to ensure a tight seal. I used the silicone from the lab inventory, using ~$25 worth. I ordered $10 of grease from Amazon.

4: A circuit board with common components and a vacuum sensor. All of the components other than the vacuum sensor will come from the lab and I estimate their cost at less than $5. I am testing a variety of vacuum sensors and hope one that works will be less than $10 and commonly available from either amazon or digikey.

5: A vacuum pump, assorted hoses and connectors. I ordered a relatively high cycle vacuum pump for this project as I intend to run it for a long time, but any vacuum source would likely work. I estimate this cost at ~$150.

Total cost for project (including pump) = ~$250, which compares very favorably to commercially available systems of a similar scale.

What parts and systems will be made? What processes will be used?

I will make the vacuum chamber (and mold), the lid (and mold), the gasket (and mold) and circuit board. I will use large format machining, laser cutting, precision milling, electronics design/production, molding and casting and composites layup to finish all of these tasks.

What tasks need to be completed?

I already have the lid and gasket produced, the mold for the vacuum chamber is designed and under production and all parts are ordered.

Remaining tasks include: producing the mold, casting and finishing the chamber, testing electronic components, designing the circuit and assembling the final circuit.

What questions need to be answered?

My primary questions revolve around the electronics component of this project. I need to determine which sensor is appropriate for my application and then how to create a circuit around its capabilities. Additionally, I intend to do some basic design evaluation to ensure I am producing a safe device within reasonable parameters.

What is the schedule?

I hope to finish the mold by 6/2, cast it on either 6/3 or 6/6 (depending on when the material arrives) and then finish it the next day (I will likely seal the chamber with a thin coating of epoxy and maybe burlap to improve strength and protect it.) In parallel, I intend to test electronic components as they arrive and have a designed circuit board no later than 6/5. Hopefully this full project can be assembled and tested before 6/10.

How will it be evaluated?

The primary evaluation for this device will be whether it holds a vacuum or not! If successful, it will be able to easily degas large molds and dehydrate green wood overnight. Hopefully evaluation will be relatively straightforward here, either the project will work or it will not!