Designing a Component

2012 June 19
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The roaster project will ultimately be made up of thousands of parts, each of which will be designed by me or by another designer. While it is impractical to tell the story of each part, I thought it might be interesting to tell the story of one part. In this case: part number 1B-001, the “Upper Plate” of the bowl carrier assembly. It is about 20″ square and made of 1/2″ thick machined cast aluminum.

Before a part can be designed, the basic concept of how a completed machine will work must be thought through. This is the initial sketch of how the bowl support system might work. It included the idea of a square tube frame with four shafts that would guide the movement of some sort of carrier up and down.

The idea of what a carrier might look like began to take shape in rough sketches. There would need to be upper and lower sets of linear bearings to make sure that the carrier would not have too much play or twist. This would likely take the form of an upper plate and a lower plate with some sort of connecting pieces that could stiffen the structure without adding lots of weight and excess metal.

An ‘X’ design for the plate seemed efficient by concentrating metal just where it is needed. The vertical elements would fit into the ‘X’ pattern.

The simple shape needed to be refined to take into account the other components that would be joined with the upper plate. This sketch started to conceptually detail some of those elements.

I started to research what purchased components would be assembled with the upper plate. The bearing for the the bowl drive shaft is one such part. I needed the specification sheets for each component to understand the performance and dimensions of each, so that it would mate perfectly with the finished part.

The next step was to do a series of design study sketches for how other components I was designing would fit. In this case, I had decided not to weld the vertical supports to the plate and, instead, bolt them on. This required ‘L’ shaped¬†stiffeners ¬†to form the 90 degree connections. These would bolt to both the vertical supports and the upper plate.

Other studies were drawn to show how parts would be bolted together and assembled. All of this helped me decide on bolt sizes and, therefore, hole diameters.

At this point, the thought process was complete and the design studies drawn. It was time to draw the actual mechanical drawing for the part. I drew it to scale and in the nomenclature used by mechanical engineers for describing parts and dimensioning. At this point refinements such as cooling fins and smoothing radii were added.

I also created a table for the coordinates of the various holes in the upper plate, including the purpose and size of each hole. Normally this would be done in CAD, but I manually calculated the rotation of holes to each arm of the ‘X’ using old school trigonometry.

At ACME Metalworks, they converted my drawings and hole coordinates into a drawing and code that the automated milling machines can use. The file was then sent to the mill for production.

The final product was machined from 1/2″ cast aluminum.

I assembled the upper plate into the bowl carrier assembly to check the fit of all parts. It fit perfectly! … And that is how the design process works for each of the components in the roaster project.

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