20.5-Inch-Mirror-Blank-Project: Difference between revisions
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== Next Step For the 20.5 Inch prototype test design == | == Next Step For the 20.5 Inch prototype test design == | ||
*use the rubber mirror positive to recast the plaster positives of the subpieces. Caste rubber negatives so in the the nub sub parts can be cast much more easily than | *use the rubber mirror positive to recast the plaster positives of the subpieces. Caste rubber negatives so in the the nub sub parts can be cast much more easily than the recovery method that I used. | ||
*For purposes of casting the dog bowl for initial development models the original rubber mirror positive can be used with a circular fiber board piece with tapered edge to facilitate release. This must be done because the depth of the overall mold must not be reduced by the thickness of the nub sub plate casting thickness. | *For purposes of casting the dog bowl for initial development models the original rubber mirror positive can be used with a circular fiber board piece with tapered edge to facilitate release. This must be done because the depth of the overall mold must not be reduced by the thickness of the nub sub plate casting thickness. | ||
Latest revision as of 23:57, 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[edit]
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[edit]
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.
Next Step For the 20.5 Inch prototype test design[edit]
- use the rubber mirror positive to recast the plaster positives of the subpieces. Caste rubber negatives so in the the nub sub parts can be cast much more easily than the recovery method that I used.
- For purposes of casting the dog bowl for initial development models the original rubber mirror positive can be used with a circular fiber board piece with tapered edge to facilitate release. This must be done because the depth of the overall mold must not be reduced by the thickness of the nub sub plate casting thickness.