20.5-Inch-Mirror-Blank-Project: Difference between revisions
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Due to the difficulties of demolding what turns out to be a very heavy refractory mold after its been cast against the rubber mirror positive I had to use a piece wise approach. In order to salvage the effort quickly I masked off various parts of the rubber mirror positive and made the nubs in a jig saw puzzle approach. | Due to the difficulties of demolding what turns out to be a very heavy refractory mold after its been cast against the rubber mirror positive I had to use a piece wise approach. In order to salvage the effort quickly I masked off various parts of the rubber mirror positive and made the nubs in a jig saw puzzle approach. | ||
These sub pieces of the nub pattern were printed on the huge kinko's printer and this printout used as a template for cutting holes of this shape into fiberboard. Then the subpieces were cast out of the refractory material. These sub pieces were then laid down in a dog bowl cast against the rubber mirror positive with a circular fiber board covering the nub holes. Thus a full mirror mold could be assembled rather than being made in one piece. | |||
Revision as of 23:49, 10 March 2007
Originally I started with a 16 inch circular cutout mirror blank. Circular is a bad choice due to concentrating stress in the narrowest part of the webbing. The 20.5 inch casting was designed with a hexagonal webbing. The photo on the right shows the general layout. The original autocad dwg file is here: Media:20.5-Hex-Pattern-Layout.dwg
Mold Master Generation
All the techniques used to generate the 16.2-Inch-Mirror-Blank-Project were used here to make the plaster master. The plaster master is destroyed generally by the de molding process of the silastic rubber mirror blank positive.
The outer rim of the master also has the 5 degree taper in the with the bottom diameter being smaller than the mirror faceplate diameter.
Conclusions
Due to the difficulties of demolding what turns out to be a very heavy refractory mold after its been cast against the rubber mirror positive I had to use a piece wise approach. In order to salvage the effort quickly I masked off various parts of the rubber mirror positive and made the nubs in a jig saw puzzle approach.
These sub pieces of the nub pattern were printed on the huge kinko's printer and this printout used as a template for cutting holes of this shape into fiberboard. Then the subpieces were cast out of the refractory material. These sub pieces were then laid down in a dog bowl cast against the rubber mirror positive with a circular fiber board covering the nub holes. Thus a full mirror mold could be assembled rather than being made in one piece.