The Plastic Within
By Craig MacKenzie, CP, RTP(c) .jpg) The use of 1/8-in. plastic on the inside of laminated sockets has been around for a few years now. It is mainly used to reduce the leak rate of high-vacuum sockets by providing a barrier from the carbon fiber. But at Velocity, we use thin plastic on everything. It reduces production time and gives the socket a glass-like appearance. Since the plastic takes the place of the inner PVA bag, there is no need to seal or dry the cast before lamination, and it allows the use of an alignment jig with a one-stage lamination.
There are things you have to remember when using plastic. Changes to the socket can be made by heating from the outside with a wet towel held on the inside to keep the plastic from blistering. Before lamination, the plastic needs to be sanded and cleaned with isopropyl alcohol to prevent delaminating. And most important, you'll need practice pulling the thin plastic.
When pulled over Pelite
™
, the heat from the plastic seals the Pelite where it has been sanded, giving it a smooth finish. It can also be pulled over a polyethylene liner as long as a nylon is used between as a vacuum wick.
The following are the steps to transfer a dynamically aligned check socket in the alignment jig with a one- stage lamination.
- Fill the cast in the alignment jig 2 in. above the trim lines.
- Remove from the jig and smooth plaster cast.
- Use a section of 2-in. pipe to raise the cast 2 in. above the platen (Fig. 1).
- Heat the plastic for three minutes at 350 F or until the plastic droops 4–5 in.
- Pull the plastic over the cast quickly; the plastic cools fast (Fig. 2).
- Cut the plastic off 2 in. above the top of the cast.
- Heat the plastic with a heat gun or propane torch and fold the excess plastic onto the cast (Fig. 3).
- Sand the plastic with 120-grit sandpaper and clean with isopropyl alcohol.
- Place the cast back in the alignment jig.
- Wrap electrical tape around the cast 1/2 in. above the distal end (Fig. 4).
-
Mix Bondo
®
with pigment to match the final color of the socket.
- Mound the Bondo on the mounting plate and lower the cast into the Bondo (Fig. 5).
- Transition the Bondo from the plate to the electrical tape.
- Allow the Bondo to set for 15 minutes.
- Remove the electrical tape.
- Remove the cast with attached mounting plate from the alignment jig.
- Install the laminating dummy on the mounting plate (Fig. 6).
- Lay up the socket as normal, tying all the layup material into the groove in the plate.
- Reflect all the layup material down, exposing the lamination dummy (Fig. 7).
- Laminate as normal.
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 After laminating, remove the lamination dummy and trim as normal. Using this technique eliminates any cleanup on the distal attachment (Fig. 8) and leaves the inside of the socket looking like glass (Fig. 9). The technique of pulling 1/8-in. plastic may take time to perfect. After a while, you will get a feel for the plastic; speed is the key. Smaller wrinkles in the plastic can be removed with a heat gun and a small roller. We buy our plastic from a local supplier and get a great deal as long as we purchase a full sheet.
A full sheet is 18 squares cut 16 in. by 16 in. With a quantity order, our supplier will cut the plastic and deliver it for free. Check with your local plastic suppliers; you might be surprised at the type of plastic that they carry or what they will stock for you. Bondo is a trade name for automotive body filler. You can get Bondo from any automotive supply, Target, or Wal-Mart.
Craig MacKenzie, CP, RTP(c), is the owner of Velocity Labs Inc., Orlando, Florida, and president of Evolution Liners Inc., Orlando. He may be contacted by phone at 407.841.6335 or via e-mail: craigm@velocity-labs.com 
Table Of Contents - June 2006
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