Progress for Week 6 of Building the Roaster

2012 May 23
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While we traveled in California, Acme Metalworks was machining many of my parts for Module 1. As a reminder, Module 1 is the roasting bowl, its carrier, and the drive system. This happens to be the heart of the roaster and the most critical module of all. The alignment of the bowl and its ability to spin without wobble and to be moved up and down very precisely is absolutely essential to the proper operation of the roaster.

Previously, the bowl had been cut and machined to the right shape. Holes were bored for the drive hub which supports the bowl and connects it  to the drive shaft. The bottom curvature was accurately measured and now the hub was machined for an exact match.

The carrier for the bowl, its drive shaft, and the drive motor was completed and given to me in pieces to assemble. The carrier is machined aluminum, comprised of an upper and lower plate attached with vertical web plates. Obviously this could have been a welded assembly, but given the fact that it must be very precise (welding could introduce warpage), would be difficult to fit into a machining station after welding, and that it is a single machine, we chose to bolt it together. A production machine would probably use welding to save cost.

The upper plate holds the thrust bearing (the bearing fits into the recess in the photo) and the upper shaft bearing. Both are lubricated with high temperature grease.

The upper plate also has cooling fins to help bleed off heat transmitted to the bearings from the bowl. There will be a thermocouple or RTD bolted to the plate near the bearings to monitor the temperature.

The entire carrier will move smoothly up and down approximately three inches. Four precision vertical rods will guide the carrier on special linear bearings (eight of them). Both the upper and lower plates have machined tabs to which we shall bolt the linear bearings.

The linear bearings are being purchased from a U.S. manufacturer.

 

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