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Week 7 - Molding and Casting

The Task

Design a 3D model, machine it and cast parts from it.

The Execution

Design

This week I chose to make a mold of myself using the 3D mesh created on the PrimeSense. See Week 5 - Scanning

The raw mesh needed to be modified in rhino in a number of ways.

  • sliced in half so only the front face is used - this allowed me to machine and use a one sided mold, reducing the machining time by half.
  • Build a 'frame' around the model to generate 'walls' in the machined wax
  • scaled to fit in the dimensions of walls of the wax block

    • The result:

    Export as binary .stl

    Notes:

  • Need to consider bit thickness and clearance when designing small gaps such as at the bottom of my model
  • Bit length will limit the depth of cut possible.

    • Generating the tool-path

    File prep here is for the Shopbot so I had 2 options available; Partworks or Fabmodules. Partworks gives you a lot of room for tweaking and customisation but is a more lengthy process, I chose Fabmodules for this job.

  • make stl-sbp
  • open .stl, make png
  • I then used the following settings for the Rough Cut


    • And the finish path


    >> make path >> make .sbp

    Milling

    The wax block can be attached to the table of the shopbot using double-sided tape.

    Zero the coordinates to the wax block, open file and run.

    Runtime for the rough-cut was 1:02:15

    And for the Finish-Cut 00:38:14

    Casting The Mold

    The machined wax positive should be thoroghly cleaned free from any loose wax or dirt before pouring the mold material

    Here, we are using the Smooth-On Smooth-Sil 940 to make a flexible negative mold which can then be used to replicate the original model using, plaster, resin, chocolate..

    The 2-part kit, has a working time of 30mins and drying time of 24hrs.

    After thoughorly mixing, the mold was filled then tapped gently on a flat surface for 5mins to remove all the air bubbles.

    After Setting

    To fully cure the silicone mold, it was baked for 2hrs at 80C then 1hr at 100C.

    Following this a trial plaster model was made.

    There are clearly some issues with the quality of the model: The mold was not fully filled into the beard area and there are a lot of air bubbles on the surface.
    Using a more fluid mix ratio to allow the mold to fill more evenly, followed by the tapping method to remove the bubbles - may be a resolution.