(Frequently Asked Questions.)

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Pattern Making

Pattern making is the heart of foundry practice.

Patterns for bonded sand molding:

Traditionally made of wood, patterns can be made of anything strong enough to withstand the pressures of being rammed in the sand.

There are a few considerations in making good patterns.

  • Patterns need to have draft. That is to say the sides need to be slightly tapered so the pattern will release from the sand.
  • Patterns can not have undercuts that will prevent them being pulled from the sand. If your pattern must have an undercut, a two piece pattern can be used.
  • Patterns should be painted to give a smooth surface and to seal them from moisture.
  • Avoid sharp corners in your patterns. They make weak areas in the casting. Use a wax or putty to round off right angles (filets).
  • Allow your pattern to be slightly oversize to make up for the natural shrinkage in the metal you are casting. Consult a shrink table to determine how much oversize you need.

There is a good book available here: Wood Pattern Making

Patterns for lost foam casting:

As the name implies, these patterns are made of foam. This can be bead board, like packing material, or expanded styrene insulation from a building supply store. (The pink or blue stuff.)

Usually cut with a hot wire cutter, the foam can be glued together to make larger pieces. Spray adhesive, white glue or low temperature hot melt glue guns have been used successfully. You might want to test an unknown glue to make sure it doesn't eat the foam you are working with before actual pattern making.