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Open pour molds
By Moldshop R/x with Rabbit
| 1.Plinths. A plinth is simply a pedestal on which a narrow part can be placed to raise it into the mold medium. It can be designed to act as a feeder reservoir and to leave minimal flash in a discreet location. As seen here. |
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| Thin plas sheet trimmed to fit the bottom contours & built up with sheet & rod to aid filling. |
2.Cross section
Some broad flat pieces have a thin cross section which must be thickened to allow the resin sufficient space to fill a broad area. Wax like the cheese comes in, can thicken those parts as seen here. |
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again a plinth is used to aid mold filling. With the plinth secured to a piece of masonite or styrene (Minimum .060" thick.) construct a wall that is 1/2" taller than the part being molded no wall should be closer than 3/8" to the part, again masonite or styrene held with hot glue works well. Spray shellac on masonite helps RTV to come away clean. Mix RTV deair* & pour. |
2 piece closed molds
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1. The parting line.
A 2 piece molds need to split upon a natural contour of the part,this wavy (somtimes.) concentric seam is the parting line. Modeling clay,( the type with goofy animals on the box) is formed into a bed, on mason/styr sheet. The part is placed on top and more clay is pushed up to the parting line |
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smoothed with dental tools until a sharp perpindicular interface is achieved.
Trim the bed with a knife, into a rectangle.
2. Keys & sprues.
Using your cheese wax create channels up to the part, make feeder sprues capacious enough to provide plenty of resin to piece. If possible to a discreet or hidden spot on part. With a small loop of music wire glued to a dowel, carve small trench's into clay, these "keys" will keep the two halves aligned when used. Coat overall with Krylon "crystal clear", assemble wall only do not glue to base, but seal bottom with clay or wax. Mix deair* & pour RTV.
When cured remove mold from base. Taking care not to disturb the part, remove clay from bottom of mold box,(Leave walls assembled around mold.). If needed add more feeder sprue and breathers using styrene rod. |
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Coat part & exposed RTV with "crystal clear"enough for a contiguous film. Pour second half, when cured you should have something like this. |
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Contact me at josborn@happinessismandatory.com
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