Fab Academy 2013

FAB LAB UNI | Lima - Perú

Molding and Casting

Milling a MDF mold and cast a mallet.

Materials & Tools

For Mold

  • 20mm MDF board
  • MDF glue or wood glue
  • Vises
  • Sand paper
  • Some wood screws
  • Jigsaw or wood saw
  • CNC mill machine: Shopbot PRSalpha 96-60
  • Ball point ¼" end mill
  • Ball point ½" end mill
  • Flat point ¼" end mill (long shaft)
  • For Casting

  • Floor wax
  • Baseline
  • Polyester Resin
  • "Cobalt" (Activator)
  • "Peroxid" (Catalyst)
  • Monostyrene (solvent)
  • Nitrile Gloves
  • Gas Mask
  • Vessel and stick (for mix all the components)
  • Mold Design

    In this assignment I made a split mold, to create mallets for the air hockey table (for my Final Project). It's a very simple piece only need a revolve operation. Of course the unmolding angles are considered in the CAD draw.

    (a) Draw dimentions (b) Section view (c) Render

    Then create the mold cavity and the mold core CAD draw. The mold core have over flow holes Finally save it in .stl format.[.STL Files]

    Mold Manufacture

    Step 01.-If you have a wood block you can jump this step. To create a wood block, cut several pieces of MDF board, and then paste it together and press it with the vises. In this case I used four 20mm layers to create a block of 80mm of height.
    Step 02.-Screw the block of cavity mold to a piece of board. Take care and screw where the mill wouldn't pass inside de mold cavity. Then screw the piece of board on the Shopbot bed.
    Step 03.-Start the milling process. Personally I used 3 types of mills (¼" and ½" Ball point and ¼" Flat Point end mill) and 2 softwares to create the 3D paths(PartWorks and PartWorks-3D) Ball point ½" end mill
    (Rough Cut-PW3D)

    Ball point ½" end mill
    (Fine Cut-PW3D)

    Ball point ¼" end mill
    (Rough Cut-PW3D)
    Ball point ¼" end mill
    (Fine Cut-PW3D)
    Flat point ¼" end mill
    (Profile Cut-PW)

    Step 04.-To fix the other part of the mold screw the MDF more than normal (introduce the head of the screw inside the MDF). For this part I use ¼" Flat Point end mill with long shaft and PartWorks to create a pocket around the cilinder to create a gross profile for the 3D milling process.
    Step 05.-Star the 3D milling of the center protude, y use for these process the Ball point ½" end mill. Rough Cut-PW3D Fine Cut-PW3D

    The Result is like the photos below:


    First spread the vaseline in all the mold surface, If you use floor wax you need to spread, at least 6 layers of wax.

    Spreading the wax The result

    For Casting, the process is too simple, only mix all the components in the correct proportion (Activator 1.5% and Catalyst 0.5%). The Monostyrene is for dilute an get the correct viscosity to reach all the parts of the mold.

    Adding the activator Adding the catalyst Mixing (also I add blue dye)

    Final pour the resin in the mold and close the mold until you see the resine exits the overflow holes.

    Pouring in the mold Covering and pressing

    If all the process was correct you can unmold in a couple of hours, depende of the temperature of the ambience (coolest take more time).