Prototyping: Part 2 – Design & Fabrication

2011 May 16
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Special thanks to Jamie Mulhern for taking all of the photos in this post, except the last.

Garage Sale Table

One thing I appreciate about my primary machine shop (Acme Metalworks) is that they have their heart in the project. Since last post, I had been designing a sturdy, basic table for them to fabricate that would be the framework upon which the bowl and motor would be situated. Tim, President of Acme, called me later in the week and told me he had found something workable at a garage sale! Since the table I was designing was strictly for prototyping, it would be a sunk cost. Now I get a cool looking table with a rusty patina as the base for the thing! I will design the prototype around our “found” table.

The bowl has had some machine work done on it. First, the dead center was found in Acme’s precision quality assurance lab (they make some very precise parts for missiles and the semiconductor industry). They found that the bowl was remarkably true (symmetric, no out-of-round issues). We then welded on a back plate through which we will then bore a precise hole, followed by threading the hole for the drive shaft.

With the new table and the bowl machining having already started, we discussed the design of the stationary return ring. The purpose of the return ring is to redirect the beans flowing up the side of the bowl back into the center of the spinning bowl by means of metal vanes. In the prototype, the vanes will be designed to be bent by hand into various shapes. The testing of the shapes and vane design is one of the most important reasons for building the prototype. Ultimately the bean dynamics (the movement of each bean, and the general flow of the mass of beans) must be proven in the prototype before any heat is added.

I then specified all of the components that we won’t build ourselves. These will be sourced from McMaster-Carr and our local hardware store. We discussed each component to be sure that my reasoning was sound. Tim and Tom made some suggestions and then I sent the list for Acme to place an order.

Meanwhile, I contracted with Paul at Metal Spinning Solutions (also in Gilbert) for the fabrication of the diverter cone. This is a metal cone inside the bowl which diverts the falling beans (flung by the vanes of the return ring) back into the base of the bowl. In the final design, it will also cover a hole through which the roasted beans will drop when ready for cooling. Paul spun me an 8″ dia cone at a 55° angle out of aluminum. It will be secured with an acorn nut and washer to a threaded rod screwed into the drive shaft.

All parts should arrive this week and it is likely we will begin assembling the prototype this week. I will then obtain some green coffee and some roasted coffee and begin experimenting with bean dynamics in the first prototype of the roaster project!

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2 Responses
  1. May 16, 2011

    thanks for inviting me to be a small part of the project!

    • May 16, 2011

      Jamie, you are very welcome. Perhaps you will be taking other photos for us from time to time. You have a very good eye.

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