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Outside bag forming is a proven technique to save time and money in the
production forming of anything from simple curves to complex spiral staircases. There
are several advantages:
- The form does not have to be as strong.
- The form can be used with several bags without waiting for the glue to dry.
- Less flat Spots
Here are the steps to make a curved arch or jamb.
- Glue the laminates.
- Stack the laminates and tape together using fiberglass reinforced tape. Apply
the tape so that the sticky side is away from the work. You want the laminates to
slide when being bent over the form. The tape also holds the mesh in place.
- Wrap the laminates in plastic window screen material. The mesh is required to
allow air to get put of the bag. Without the mesh, the bag would seal around the
vacuum connector and prevent the bag from being fully evacuated. The fine mesh also
helps protect the bag from sharp corners. Tape the sharp edges of the ends or cover
with cardboard.
- Slide the assembly into the bag making sure the Vacuum connector hits against
the mesh.
- Bend the bag over the form and apply clamps to hold the shape. The bag does not
do any bending, you do, the bag does all the squeezing.
- Evacuate the bag, it is now squeezing with 1800 lbs/sq.ft. Of even and uniform
pressure.
- If you have multiple bags and a manifold, remove the bag from, the form and hold
the shape with a bar clamp across the bottom if the laminates are so stiff that they
spring out.
- Repeat the process for multiple bags.
Tips:
A. Use a piece of fiberglass reinforced tape to hold two pieces together for a
spliced joint.
B. For a small or tight radius push the bag into a female form. The top of the bag is
smooth and without wrinkles. On smaller arches, the wrinkles can make a dimensional
difference.
C. Use VAK Bond 2000 urea glue, for a rigid bond and no or minimal spring back.
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