Molding and Casting

Softwares Used

Getting Started

This week I had the idea of making a flexible silicone band to go around the cuff of my final project glove. I started working on this and will document it on this oage if it proves an element key to the final product but it proved quite ambitious and I went through a number of iterations of the mould, at first believing it would only need a one part mould, it ended up a piece that would have had to be quite a complex two part mould, if not a three parter. The design and redesign of this one component took up a large portion of the time I had this week, and I still had no cuff to show for it, for this reason I decided to massively simplify in order to get the assignment done on time.

I have chosen to make a simple noughts and crosses game, with a one part mould, that people will be able to play with in the lab (on tea breaks etc.)

Designing the Mould

I did the design of the mould in Fusion 360, first measuring the size of the wax block we had for casting in, then creating space for pre-moulds for a board, four crosses and five noughts. It is a very simple pre-mould but should yeild exactly what I need after it is milled.


The exact size of the/> wax block I was to be milling. This later changed as I didn't need one as deep, and this was actually too large for the milling machine. but this was the initial base that I worked from in Fusion


I used the mirror function in fusion to quickly create spaces for the indents i would then sketch the shapes for my pre-moulds in. I extruded them 15mm into the shape


I then sketched the outlines of all my parts within the indents that I had just created, I used mirroring again to speed up the process of creating multiple partsvthat were the same.


I then extruded each part 10mm, leaving a 5mm gap that would form the bottom of my mould.`


After finishing the modelling process you must select the component and save it as an .stl file, ready for exporting into SRP Player.


Using the Milling Software

The next thing to do was to import the model into the milling doftware, define it's characteristics and tool path and then begin to mill my pre-mould


Click the 'open' button to import the model you exported from Fusion as an


This is what my model looked like in SRP Player, there were a number of parameters I had to set before I could start milling


img src="Images/Molding/confirm-size.jpeg" class="std-image">

The first thing I had to do was to check the size of the model. Here you can see that the z and y axis are inverted. This meant that I had to go back into fusion and rotate my model to the correct position.


Another problem that I ran into when exporting from Fusion into SRP Player was that I forgot to account for the width of the milling tool. This was my fault as I was designing so fast, I also made the depth of the block too deep, but both of issues were easy fixes thanks to Fusion's parametric capabilities.

To fix the second issue I made the objects thinner ,ensuring there was 4ml of space for the tool to work in, and the base less deep. I also had to rotate the entire body to fix the first issue. I used the move tool, making sure that the axis lined up with those in SRP as XYZ are at different orientations in the two softwares.


After the rotation the model size and orientation was correct


After correcting the model, I went on to use SRP to define the charactaristics of the mill and the settings required for the tool path. Then I was ready to go!

The first thing you do when defining the model in SRP is to tell the software which face is the top one, so that it knows which direction to mill from. Do this using the orientation tool.


You then must state what kind of milling you will be doing from the option shown here. This will optimise the procedure based on the characteristics of your model.


You must then remove the margins from the cut so as to ensure it cuts to the size drawn in fusion and doesn;t use more bed space than necessary. This is particularly needed if your piece is big compared to the base of the machine.


Milling my premould out of machinable wax. This process took around 4 and a half hours, so I checked that it was milling okay and then got on with some other work whilst it was finishing up.

Making the Mould

To make the mould I used Smoothe-On's Oomoo Silicone. This is a two part mixture (1:1 ratio by volume), which are liquid when separate and catalyse eachother when combined, reacting together to form a solid. It is important to stir both parts A and B before mixing them, as they must be homogenous in order to work properly and if left for a long time can form sediment at the bottom of their containers. When the two parts are mixed together the Smoothe-On website says that you have 15 minutes worth of stirring "pot" time, but I found it was around half that much, however this could have been due to the fact that my mixture was an imprecise ratio due to lack of volumetric measuring equipment, although it was still about 1:1. After it was mixed I poured the mixture into the pre-mould and waited for it to set. I had to repeat this process twice as the first time i did not paint the pre-mould, this meant i got a lot of bubbles. Below you can see images of both the first and second mould attempts



Stirring the silicone part a mixture in it's container. It is very thick so be sure to hold both the pot and stirrer when doing this. We made our stirring stick by cutting and sanding some laminate floor into shape, but anything will do. Remember you will need a different stirrer for each pot otherwise you will cross contaminate parts A and B.

When combined together the mixture became thick, however you must stir regardless to make sure that it is properly mixed. This was another mistake that I mde on my first attempt, when it was not properly mixed there were parts of the mould that had not set properly as they weren't catalysed.


After mixing the two parts together, paint the mould roughly with a small amount. This will ensure that the silicone pours with fewer air bubbles. Then pour the rest of the mixture into the pre-mould and wait for it to set. You can see below a mould i made without painting for comparison.


This is the mould I made without the paining. When it came out of the pre-mould each part needed to be cut, this was due to inaccuracy in pouring due to lack of a funnel or tip on the cup i was using. I just did this using a scalpal.


This was my first attempt at the mould. As you can see it is bubbly and the centre's of the 'O' moulds didn't form. Upon closer inspection the colour was also inconsistent.


The second pour yielded a much better mould due to the fact that I painted the silicone into the pre-mould before pouring the rest. There are less bubbles and the colour is even throughout.


The next step was to use the mould I had just made to make the noughts and crosses set. I had to wait for the mould to dry before doing this, which took about 6/7 hours to be completely done. I decided to use smoothe-on resin, which is also a two part mixture with a 1:1 ratio. It was much thinner than the silicon mix and therefore easier to mix and pour. I made surplus resin mixture so decided to fill both sets of moulds in order to show a comparison. The finished product turned out well, especially after a small amount of filing.

The two parts for the resin, the canisters needed to be shaken before pouring out to make sure that the mixtures were homogenous. It is much more thin than the silicone mix so can be poured rather than scooped out.


This is the resin in the cup, I added a white dye to change it to cloudy rather than its original clear colour. You only need a small pinprick of dye to colour the resin as it is incredibly concentrated.


The pieces setting in the moulds. Make sure you do this on a tray as the plastic is very difficult to remove from any surface it sticks to. The resin takes longer to fully set than the silicone and must be completely hard before you remove it from the mould.


This is the piece that my second attempt at the mould yielded, there are a few rough pieces but they were easily sanded down or broken off.


I just used a standard flat edged, one sided file to remove the excess material from my pieces. This ensured that I retained sharp corners.


Here you can see the board piece yielded from mould 1 compared with the filed piece from mould 2. The difference is huge and shows the importance of painting the silicone on when making the pre-mould.


I was happy with the final product of my board and pieces after I had finished filing them down and they have already been used on a break in the lab! I am still a little frustrated that I was unable to make my initial idea of a silicone cuff work, however I will try to mould and cast this at a later date if I have time.


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