How do I make a Multipart Mould?


Example:

  1. 1.The first stage of making a multi-part mould is to prepare your master.

    In this example we are making an antler.

   Draw a line along the antlers that would effectively cut them in half along the entire length. To get an idea of what I mean by this, look at any plastic moulded shape around you such as action figures or kitchen appliances; you will see seem lines that follow a similar line to that which we have drawn on the antlers. If you are still unsure ask your technician.


2.The next step is to lay a bed of clay down that will support one half of the antlers, following the line you have drawn in step 1, build up the clay until it lays parallel with the line, make this platform at least 50mm wide and ensure it runs into the antler at a crisp right angle. This process is known as ‘claying up’ and is a crucial step in making this kind of mould. Complete a platform that runs all the way around the antler. Again, if you are unsure ask.


3.The next step is to press keys or locaters (a dome shaped depression) into the clay platform at regular intervals around 30-40mm apart. A small coin is good for this. These locaters will also play a crucial role in the success of your mould.


4.At the base of the antlers (where it used to be attached to the head of a stag) we press half a plastic tube into the clay, or make one out of clay that is about 30mm in diameter. This must meet up with the surface of the antler base and will act as our pour hole once the mould is complete.


5.Next we will need to create a way for the air to escape from the tips of the antlers when we pour our casting material into the finished mould. These can be made, quite simply, by using 3mm nylon rod. Heat the rod with a hot air gun and, while still hot and soft, press into the surface of the clay until it is half submerged along its entire length. Each antler extremity tip will need one of these rods. One end of each rod joins the antler tip while the other end exits the clay platform adjacent to the pour hole we created in step 4. This may take some time, so be patient. Once all of these air vent are complete and you have ensured there is a good contact with each tip of the antler, improve this contact seal with a small amount of clay.


6.Now we may mix the first batch of condensation cure silicone. This will only need to be a small amount, as we will only be concerned with capturing detail at this stage. Once mixed and degassed, pour over the entire antler ensuring the clay platform you created in step 2 is also completely covered. Allow the silicone to flow, do not worry if a little runs off the edge of your platform or if it looks very thin. This layer also prevents air bubbles sticking to the surface of the mould.


7.When this first layer of silicone is cured, we need to mix more silicone and de-gas it. At this stage we need to add a thixotropic agent (thickener) to the silicone and stir it in thoroughly until it ceases to run. This is then applied to the first layer in circular pasting motion, much like icing a cake. This layer must be as even and as smooth as possible. Also, make sure that all the locaters, air vents, pour hole and the platform is covered properly. An ideal thickness for this layer is about 5mm, but thicker if your master is larger, consult your technician if you are unsure what is best for you.


8.Once this layer is cured, a jacket or support structure must be added. This can be made using plaster and scrim, mod-roc or fibre-glass. (See ‘Life-casting’ or ‘GP resin’ for more about these)


9.When the jacket has been added and has fully cured, the clay platform may be removed. Try not to loosen the master (the antler) in the mould as this will ruin the natural seal created by the silicone.


10. Flip the mould over and give the exposed silicone and antler a good clean until they are free of clay then apply a generous layer of Vasoline or other suitable release agents to prevent the set silicone sticking to the next layer of silicone you will be applying. Leave the nylon rod ‘air vents’ and pour hole shaft in place when you do this. Release agents must not be applied to the master itself, just the silicone and air vents.


11. Repeat steps 6,7 and 8


12. Before you remove the antler from the mould drill holes around the edge of the platform (flange or shuttering) where the two halves of the mould join. These should ideally be 100mm apart and be big enough to accommodate a 5 mm nut and bolt.


13. Now remove the jacket, peel the silicone skin off and remove the antler, the pour hole shaft and the nylon rod ‘air vents’. Replace the skin into the jacket and rejoin the 2 halves together, insert the bolts or clamp the jacket together and you are ready to cast.


 

Multipart Mould

 

What is a Multipart Mould?


Multipart moulds are a very versatile form of mould making, in that, it is possible to make a multipart mould for many different complex sizes and shapes. Multipart moulds can also be made from a number of different mould making materials such as fibre-glass, plaster, silicone, polyurethane rubber, or latex.


This type of mould making is best suited to complex shapes that curve on multiple plains of space. A multi-part mould commonly involves other methods of mould making, especially skin mould making techniques. For example; a skin of silicone maybe applied before a multipart jacket is added. This combination ensure that detail is preserved by the silicone while the multi-part jacket supports the form.

   

Second skin of silicone for multi-part mould-making

   

Clay flange, keys and air vents for multi-part mould-making

   

First silicone pour for a multi-part mould

   

Finished, empty multi-part silicone skin with fibre-glass jacket mould