In the past I tried using clear plastic bottles and had the same problem- the plastic distorted and cooled too fast. But I ofund a tutorial that showed how to do it successfully. The other week I found and downloaded a 32 page booklet on how to build a modeling vac former from either here at Zealot or at papermodelers (now I can't seem to find it). At the back it spelled out exactly how to successfully do it with a soda bottle and a heat source.
You will need:
A) A bottle with a smooth shoulder and neck. Some brands with a small ridge, like Pepsi bottles might work- the ridge sometimes disappears when heated.
B) Your positive mold- make it fairly sturdy- wood, foam,plaster (I used 1mm board coated with CA then sanded).
C)A heat source- I used a paint stripper heat gun. VERY effective.
D)Small pieces of wood to act as a base and wedges.
1)Cut a hole in the bottom of the bottle just large enough to fit your mold. Place it against the inside shoulder of the bottle as clase to the neck as possible. Insert the base and wedges in the bottle underneath the mold wedging it firmly against the inside of the bottle. Viewed form the side(with the bottle laying on its side) the bottom of the mold should be above the neck of the bottle.
2)Apply heat slowly and evely to the bottle around the canopy. The bottle will shrink conforming to the mold. Be careful to make sure the base and wedges won't inhibit the plastic from shrinking to conform to the mold.
3) Let cool, cut out, and admire your newly acquired skill.
My first go at this wasn't completely successful, but it was light years better than my previous attempts.
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