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Object Record

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Object Name Tool
Catalog Number 1997.46.1
Collection Tool
Other Name Lapping Machine & Shellacking Press
Date c.1875
Description Many of the components of a watch have surfaces that require a uniform mirror finish. Polishing machines such as this were used to accomlish this task. Flat unpolished pieces were placed in hot shellac on one side of a round disk. The disk was then compressed and cooled in the shellacking press, ensuring that the parts would be secure and flush against the disk. In the case of screw polishing, screws were placed in disks with circular rows of countersunk holes, allowing only the top portion of the of the screw head to be exposed for polishing.
Next, the disk was placed on the polishing plate and an abrasive coumpound was applied. The spindle, which was geared to allow it to move in an orbital pattern, was realeased and lowered. The offset center was placed in a hole at the rear of the disk. The machine was activated and parts were ground and polished against a cast iron or glass plate. Various grits were used to create an increasingly finer finish. While the machine was in operation, the cast iron ball at the top of the spindle applied even pressure to the work. When the polishing operation was comlete, the disk was placed in a strainer and dipped in alcohol, dissolving the shellac and leaving clean finished pieces.

Shellacking press has small platform to place disks to be compressed.
Lapping machine has round polishing plate made of thick glass. Spindle above moves in orbital pattern. Cast iron ball at top of spindle applied even pressure.
Maker Maker Unknown
Material steel, iron, glass, wood, brass
Place of Origin USA

Updated by Cara M. Lower 8/12/14
Updated by Cara M. Lower 8/12/14 (Added to the beginning and middle of the description)