Progress for October 2012: Modifications

2012 October 23
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During the month of October, we have been checking what we have built and making modifications to improve certain details. A key assembly is the bowl hub and shaft combination. I was not entirely happy with my design and decided to either remake the hub and shaft or modify them both. After discussion with Tim at ACME Metalworks, we determined that the modified parts would work well and be as durable as new parts.

The problem with my design was that there was no positive stop for the hub relative to the shaft and this introduced too much play in the bowl when it rotated. An initial fix was putting a pin into the side of the hub and through the shaft so that the mounting nut could be tightened. It worked great, but my concern was that this fix would make access to the thrust washer virtually impossible. If it were to fail, the roaster would have to be almost completely torn apart to access this tiny part. Access and repairability are part of good design, so I decided to make a different modification: reduce the diameter of the shaft where the hub is attached, creating a shoulder and also decrease the hole diameter of the hub so that it matched the smaller shaft diameter.

The hub was modified by welding a sleeve into the large hole and then machining it precisely to the smaller diameter. Also a new keyway was cut. The welds were faced and made completely smooth.

This is very difficult work that takes an extremely skilled machinist. Our project machinist is Marco and, in this photo, he shows off his workmanship.

The shaft modification was much easier. A short section of the existing shaft needed to be turned down to the new diameter. This was done in a CNC machining center.

Additional modifications were done to the motor mount for the bowl drive motor. We slotted the mounting holes to allow for adjusting the alignment of the motor to the shaft.

A new part also arrived: the linear actuator for the bowl carrier. This device will lift or drop the bowl carrier 3″ in just a few seconds. Dropping the bowl is how we are able to evacuate the beans when the roasting process is done. There will also be a manual way of doing this using a cam and lever arrangement.

I continued drawing new parts for this module. The focus is on the bowl skirt which is a stationary 4″ tall ring that is barely below the spinning bowl. Its purpose is to prevent beans from falling under the bowl when the bowl is dropped at the end of the roasting cycle. My drawings are currently being converted to CAD drawings that will be sent to a water-jetting company for fabrication.

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