Prototyping: Part 1 – Design & Fabrication

2011 May 3
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The Roaster Bowl is Here

The roaster bowl finally arrived. We waited several weeks for the fabricator in Los Angeles to get around to shipping the thing (which was in-stock)! It is not easy, sometimes, having the roaster project be a single work with no prospect of future sales for parts manufacturer.

The bowl is a beautiful piece of work. It is 36″ in diameter, made of cold rolled steel about 1/3″ thick, and weighs 154 lbs. It is shaped as a 2:1 semi-elliptical bowl. It is now at Acme Metal Works (Gilbert, AZ), our primary fabrication partner for the project. They will be boring and threading the bowl as well as doing some final trim and dimension check (to ensure that is is perfectly symmetrical).

Prototype Design – Brainstorming

I learned many years ago as a young engineer that it is valuable to get the view point of machinists and fabricators when designing components. They have insight into the manufacturing process and design that comes from actually making things. Thankfully, at Acme, I have two talented men to work with on design review: Tim and Tom Eckholdt. Tom is the founder of Acme (though semi-retired) and brings lots of real world experience in all things mechanical (he is a sports car enthusiast, as well). His son, Tim, is the President of  Acme and runs day to day operations. Tim brings a very deliberate and precise way of thinking to the mix. We began to go over my initial design to critique it and determine if there are some easier ways to accomplish the same design goals.

We sat down in their conference room and sketched out on the marker board the basic design for the prototype. It is very simple. A steel table will support the bowl. The bowl will have a shaft that extends through the table and held in place by two sets of bearings. The shaft will have a gear attached to it that is driven via a conventional roller chain by a variable speed DC motor. Above the spinning bowl will be a stationary ring with adjustable vanes that allow experimentation on how best to redirect the flow of the beans back into the center of the bowl.

The table will be constructed of 2″ square steel tubing welded into a rigid frame. It will have a top and bottom made of rolled steel sheet stock that has precise holes machined into it. We discussed how best to design the table frame and then continued on talking about components.

We will be purchasing stock components such as bearings, gears, the motor, the chain, and fasteners. There are several firms that machine shops rely upon as major suppliers for these types of parts. We looked at the catalogues together and discussed the pros and cons of different grades and designs of standard components.

By the end of the meeting we had decided that I will proceed with the dimensioned design drawings and specify all of the components. Tim will begin machining the bowl, which includes welding on a back plate, boring and threading the center hole, welding tabs on the upper ring, and trimming off the upper ring. The prototyping has begun!

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