Summary
This week i didn’t need to empty my head of last week’s knowledge to make room for all of this week. A lot about this subject was still there from my time working on props and practical special effects.
It was a lot of fun messing around with these casting and moulding chemicals, and pretty much successful in what were were supposed to achieve with such a small block of wax.
What I thought I knew before
A long long time ago, in a far away galaxy, I studied Special Effects Design for Film and TV. Part of the teaching including casting and mould making. For applications such as props, sculpting and prosthetic makeup. I also worked for a while doing this, before finding more work in post-production.
So i think that i still remember the principles and procedures for this week. But i’m sure there are still things i can learn from covering this subject again. So there’s the caveat in case something goes wrong ;).
Learning Outcomes
Theory and use of things i learnt from this assignment:
- Design appropriate objects within the limitations of 3 axis machining.
- Demonstrate workflows used in mould design, construction and casting.
Lessons to take away
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Getting the smallest detail wrong in the procedure of casting and moulding, and weeks of work can be ruined. You’ll only know at the end.
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Moulding and Casting generates a lot of waste (not necessarily of nice things for the environment or your health). The proportion is greater the smaller the run of castings you do.
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Know your materials and how they act!
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It’s messy!!
Moulding + Casting Risk Assessment
| RISK | WHO IS AFFECTED | CONTROL MEASURES | RATING | DEFENSIVE MEASURES |
|---|---|---|---|---|
| Skin irritation, Eye damage, Lung Damage | YOU, OTHERS | Use of a Fumigation Cabinet / Well ventilated room | HIGH | Read the safety and data sheets for instructions and guidance using potentially hazardous chemicals. |
Moulding + Casting Guide
Moulding + casting is a mixture of craft, design, chemistry and science skills all in one. Designing the object and the mould in which you want to make multiple copies from requires the ability to think in 3D, negative and positive spaces. The practical side requires you to have a scientific procedural way of thinking and precision when working with chemicals. Weeks of work creating moulds and castings can be ruined by simple things like not mixing the correct ratio of chemicals. You will only find out if it’s gone wrong at the moment you open the mould.
Being precise in the way you mix things, the order in which you do things and other small details can reduce the chance of failure. Moulding and casting is a long and laborious set of processes which can fail at any moment. It can also generate a lot of waste, and some of that can be harmful to the environment so it is important to careful in the way you work.
It will get a bit confusing, as there will be lots of talking about positives and negatives, and those positives are negatives of something else at the same time. It may help to think through the processes not only from the start to finish, but also the other way around. Backwards from what you expect to see at the end to what you begin with.
Measuring the amount of mixed material needed to cast
To work out the weight of material needed to be mixed:
- Measure the weight of a mixing cup.
- Fill the cast with water and empty that into the mixing cup.
- Subtract the weight of the cup from the total and you have the weight of the material needed.
To work out the volume of material needed to be mixed:
- Fill the cast with water and empty that into the mixing cup that has volume measurement / or a measuring jug.
- Read measurement.
Prepare the mould
- Clean any old material from older castings out of the cast, either physically with tools or chemicals. Degrease and decontaminate with with acetone / isopropanol or similar.
- When dry, apply a mould release product as per their instructions if needed, in way that won’t obscure the details in the mould.
Mixing
- Shake / mix products in their own containers first.
- Measure out the amount of the most viscous component as carefully as possible (trying not to introduce air into the mixture)as this is the most difficult to pour an accurate amount. If needed, add non-reactive fillers / thickeners or additives (e.g. metal powder) and mix thoroughly.
- In the same mixing pot measure out the amount of other components. Take a check of the time as the ‘pot life’ countdown has started.
- With a mixing spatula mix the components together is a gentle manner, trying not to introduce air. Scrape the sides of the mixing container, the ‘corners’ where the edges meet and the spatula itself. These areas will have layers of non-mixed material hiding. Continue mixing for as long as you are able so that there an equal consistency, or, where the components start in different colours, a colour in between. The consequence of not mixing properly can lead to ‘soft’ spots that never cure in the final casting, or points of failure in the material strength.
- To be extra sure, transfer mixture into another mixing cup and mix once more with a clean mixing spatula.
De-gassing
- This is the process of extracting as much of the air/gas from the mixture using a vacuum chamber. Some materials specify that it’s not necessary, and others have such a short pot-life that makes it not practically possible.
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This example consists of a ‘container’ with a heavy acrylic see-hough lid. There is a flexible ring of silicone in the lid where the container’s rim meets the lid to ensure an air tight seal. There are 2 valves with handles on top, one to release the vacuum, and the other to open the container to the vacuum pump. A pressure measurement indicator allows you to monitor the vacuum being pulled.
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Closing the release valve, and opening the (turned on) vacuum pump starts the bubbles of gas to rise in the material. Depending on the material, the bubbles could be small and rise slowly, pulling the level of the material up a just a little. Or the material could mean that the bubbles get progressively bigger and more energetic, to the point where the level of the material will spill over the edge of your mixing container, losing some of material you need for casting.
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At this point you should open the release valve to slow the vacuum down and lower the level of the material in your mixing container. When the rate of bubbles rising slows significantly then you know that the vacuum has pulled most of the gas out.
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Turn off the vacuum pump and slowly open the release valve. A quick change in pressure could tip the mixing container over, or blow some dirt from the bottom of the chamber into your mixture, contaminating it.
Pouring into an entry spout
- Pour slowly into the entry spout of the clean and prepared mould, leaving enough room / time for the air to escape.
- Tilt, rotate, shake the mould as you do this where possible to help the air to escape and the material to reach the difficult areas.
Pouring thicker mixtures
- With mixed materials that are of a higher viscosity that aren’t easy to pour, or a mould that is a difficult shape to pour into, you will need to do something different.
- With the mould open, take a the mixing spatula and ‘spoon’ the mixture into the lowest parts of the mould pieces and spread the mixture around. With detailed moulds the use of a brush to ‘paint’ the mixture into the fine details. Fill the pieces with as much material as possible, whilst trying to expel any trapped air and not getting any of the material on the parting line edges of the mould.
- Close the pieces of the mould, and tilt, rotate, shake it to move the material around and expel air inside.
Don’t throw away the mixing pot with excess material in immediately. Wait for the mixture to cure. First, because its easier and more eco-friendly to dispose of when set. Second, you can test the mixture in the mixing vessel for de-moulding/curing readiness without opening the mould and potentially destroying the casting.
De-moulding
- Not before reaching the advised de-moulding/handling time after pouring, gently try to separate the mould pieces. Assuming the mould design was perfect, there shouldn’t be too much trouble. Begin by going around the mould to multiple points and tentatively prising them apart.
- Use tools, wedges or compressed air to help this process if needed.
- Once out, the casting is not at full material strength and maybe tacky to the touch. Be careful where and what on you place the casting on. The process of curing is usually an exothermic reaction and can continue to give off fumes.
Sprue / Flashing etc
- Once the casting has been de-moulded, the material maybe in a softer state than at full cure that makes it physically easier to remove sprue, flashing and any excess material not needed in the finished cast.
Curing
- The easiest process as you just have to wait. Usually in the amount of hours or days. The chemical reaction within the casting will have finished; cooled if it was an exothermic reaction, and gained its full strength.
Finishing
- Once cured you are safe to handle the casting without any problems. Any adjustments you need to make to the casting material such as sanding, drilling or painting can be done now.
Shopbot Machine (3D milling)
For 2D limitations, Operating guide, Safety instructions etc:
See Week 7.
Most used settings for 3D (in wax)
| Setting | Value |
|---|---|
| Stepover | 3mm (or 60%) |
| Spindle Speed | 6000 r.p.m |
| Feed Rate | 30 mm/sec |
| Plunge Rate | 20 mm/sec |
Limitations (3D)
- It can only mill in 3 axes, meaning no under cuts are possible.
- It can only go as deep (Z axis) as the exposed milling bit is long.
Group Assignment
- Review the safety data sheets for each of your moulding and casting materials.
- Make and compare test casts with each of them.
What we did
Data sheets / Safety Sheets / News Bulletins
Usually they accompany the material products you’re going to use, or should be downloaded from the companies website before using.
The information these sheets describe what the product is, in regards to what chemicals are contained. They will also describe:
- How they should be handled.
- How they should be disposed of.
- Directions in case of accidents.
- What reactions it will have with other materials in the moulding and casting processes.
- How it affects the environment.
- Storage instructions.
- And many more!
The important practical words you need to look for when moulding and casting are:
| WORD | DESCRIPTION |
|---|---|
| Pot life | The amount of time from the moment you start mixing the components in a pot to when it starts to set. This can be in amounts as low as a few minutes. |
| Mixing Ratio | In what proportions you need to mix the 2 or more components, usually by weight or by volume. |
| Shelf life | The amount of time you have to finish using up the products from when you first open the sealed containers of the components. Or the amount of time from when the products left the factory to when they are likely not to work properly. |
| Handling / De-moulding time | The average amount of time before you can safely remove the cast from a mould or handle it. It may still be tacky/sticky and not at full material strength. This may be the optimal time to do dome finishing work, flashing or sprue removal from the cast. The material also may also shrink whilst curing and be difficult to remove if left in the cast until curing time. |
| Curing time | This is the average amount of time for the material to fully complete the chemical reaction and gain full material strength. This can be in amounts of hours! |
Choice of material
Erwin and myself (more myself) wanted to use the Smooth-on Flex60 rubber product. This was going to be the material i would probably use in my individual assignment. The mould of a knife was also in the same vein as what my cast piece would be (a rubber hammer). From this test i also wanted to get a better idea if the material needed some sort of support (a rod of some sort) inside to hold up the shape of the cast.
Preparation
We read the data sheets / news bulletins for the Flex60 urethane rubber. It has a pot-life of 2.5 minutes, so there would be little time to waste. The best approach would be to prepare everything as much as possible, placing all the things we need for every part of the process close to hand.
Preparing the product included shaking it in their bottle before opening, having the mixing cup and tools at our side. Cleaning the mould of debris from the last casting - We didn’t want problems from cross-contamination from old material and chemicals. De-greased the mould with soap and water and then dried the parts of the mould. In case of accidental spillage of the material we had some cleaning materials at hand.
We put on disposable gloves and took other personal safety precautions, and turned on the fume extractor in the fume cabinet.
How much material to mix?
Part of the preparation was to fill the mould up with water and pour that into a missing cup to measure. This was a little difficult as the mould parts were long,flexible and the cast being a knife doesn’t have much, so the water would fall out easily. I filled up on half of the mould twice and emptied into the cup.
Taking the weight of the mixing cup away from the weight of the mixing cup and water gave us 18g. At a ration of 1:1 A to B components by weight, we would need 9 grams of each.
Mixing
We poured the thickest most viscose component first, as this is harder to pour in the accurate amount. Too much by accident and you can add more of the thinner component more easily to match.
Then we started to add the same a mount of the second component to the mixing pot. Now the count down for when it would set began. The data sheet suggested mixing for 60 seconds maximum, so as quickly as we could, whilst still being gentle enough to not introduce bubbles, we mixed the material. Scrapping the residue off of the side and off of the stick regularly to ensure a homogeneous mixture. The colour mixed to a nice pearl translucent even colour.
Pouring
Rushing, we tried to pour the mixture out of the mixing cup. It didn’t really. It would be too slow to run in the time we had before it set, so we changed our technique quickly. With the mixing spatula we spooned it in and pushed the material into the lowest parts and details of the mould pieces. Spreading it around as much as we could, we quickly closed the mould pieces and pressed down on them. And then we started hoping it would work.
We placed the mixing pot with the residue next to the mould in fume cabinet. We would check this residue to see how the curing process was progressing and not be tempted to open the mould too soon to check instead.
Demoulding
Once the residue was hard enough (around the de-moulding / handling time specified in the data sheet), Erwin opened the mould. There we could see the first indications on how successful the casting was. Still sticky / tacky to the touch, Erwin left it in the fume cabinet to finish curing (24hrs as stated in the data sheet).
Curing
The next day i removed the casting from the mould half. Curing had finished and the cast piece was ‘rubbery’ ;) to the touch.
Finishing
Cutting off the sprue and flashing from around the parting line was a little difficult, due to the nature of the material cast. Rubber tends to bend and spread out when pressure is applied to it. Even with a fresh blade, cutting the edges wer difficult or impossible with a stanley knife. I found a pair or normal scissors which managed to roughly cut the excess material away. Fine scissors with the blades curving up, like those used in sewing and embroidery would work better to cut the moulding seam as close to the shape of the object as possible. Another option to grind away rubber and flexible material would be to use a Dremel rotary tool with a ‘Blue corondum’ high abrasion stone tip.
Mistakes & Issues
Overall
The combination of this material with a very short pot-life and the flexible thin mould probably wasn’t the best. The material sets so quickly, it wasn’t going to be fluid enough to pour in to the mould, as well as have the time/ability for air to move and escape though the mould.
The technique to use would be to ‘spoon’ it in to the mould halves, filling both sides as much as possible to their boundaries. Then quickly pressing them together and applying ‘back pressure’ (squeezing them together).
Mould needed support.
The mould was long and flexible by its material. It really needed some rigid support for it to hold up in a vertical manner and pour through the designed holes.
Not enough material in the mould.
The size of the air bubble in the handle suggests that not enough material was in the mould.
Individual Assignment
- Design a 3D mould around the stock and tooling that you’ll be using, mill it (rough cut + (at least) three-axis finish cut), and use it to cast parts.
This is a 3-way or 3 phase method of casting.
- Make a positive of the model and the bounding walls of the mould’s negative.
- Cast the mould from this negative.
- Final casting from the mould that contains the original model’s negative.
My original idea when i first heard of the assignment was to create a ‘breakaway’ glass bottle like the ones used in practical effects for film and TV. Part of the process would be done using a ‘rotary casting’ machine like Paul Cairns (2021 student from Vancouver - Moulding + Casting week).
Milling the outer profile of a bottle in a 2 part mould, i would add a small amount of material into the mould and then spin it in the casting machine to create a seamless hollow bottle. But without a rotary casting machine being accessible, i then change the idea to creating half a bottle in 2 parts (outer profile and inner profile). From which i would cast a half bottle twice and fix them together somehow.
But the special effects company in Amsterdam had no ‘Smooth-on Smash Plastic’ in stock. So another plan. Sticking with the special effects prop idea, the next comical thing would be a rubber hammer!. We had a flexible urethane rubber product (‘Smooth-on Flex60’) so it was possible.
What I did
- WAX
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Trim and square off flashing from re-cycled wax casting
The block of wax wasn’t straight, flat or on any side square to any other. To get to close to measuring any part accurately, some work had to be done to the wax block that came out of it’s mould. Using various tools, knives, files and hacksaws, i cut off material sticking out and tried to flatten edges and planes.
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Measurements
I then recorded the smallest and largest values of its width, length and thickness. My model will have to fit inside the lower measurements and the higher measurements will be the ones i give to vCarve Pro as the document settings.
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Design
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Positive model
So I designed the hammer to have similar proportions to a real life size hammer. The wax block was too small to make even one side of a life sized hammer, so i had to scale it down to fit the measurement boundaries.
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Join half wax block
Once i had the model sized correctly, I combined it with a model matching the wax block with half the thickness. Aligning the model’s centre point with the top of this ‘half’ wax block.
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Add boundary walls, spouts, breathers etc.
I then added a boundary wall to all sides (and the middle) of the wax block model, extruding the sides to match half the height. I positioned the ‘hammer’ model to fit into the pocket now created in one side. I added a spout for pouring in material and breather hole at the farthest point of the model from the spout. Both were long enough to connect to the boundary walls.
I copied the model, the extra spout and breather hole. Rotated and positioned it so that it was a mirror image of the original side.
For registration points, i created cut-outs on one side, and extrusions on the other to the same depth/height. Both sets had the same footprint dimensions and arranged as a mirror image of each other.
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Mill
- Setup
I placed the wax block in a middle part of the Shopbot’s working bed, and screwed down some strips of wood to hold it in it’s position.
For more detailed description of vCarve Pro see Week7.
I opened up vCurve Pro on the computer and created a new document, with the minimum value measurements for length and width, but with the maximum value for depth (vCurve gave a error ‘model too big’ if i did otherwise). I imported my .STL model file into vCarve. Centred the model and unchecked ‘Discard data below Zero Plane’ so not to lose half of the model in future steps (why is this an option??). The model’s dimensions were oversized (apart from the depth) but one of the red lines denoting the working area was still visible above the level of the model.
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Tool paths / settings
On the right hand side are the tool paths menu. Clicking on this first shows the shows the ‘materials setup’. I didn’t change anything about the datum, thickness or anything else. Confirming these settings then allows you to get to the tool path tools.
- Roughing path
Choosing the ‘Roughing tool’ path button, I went down the list of settings:
TOOL: Fablab 5mm 2 flute preset
Which had its own settings of:
| Setting | Value |
|---|---|
| Stepover | 3mm (or 60%) |
| Spindle Speed | 6000 r.p.m |
| Feed Rate | 30 mm/sec |
| Plunge Rate | 20 mm/sec |
Other:
| Setting | Value |
|---|---|
| Machine limit boundary | Material Boundary |
| Machining Allowance | 0.5mm (default - The virtual thickness that acts as a boundary fro the roughing tool path.) |
| Roughing strategy | Z axis - Raster X |
- Finishing path
Choosing the ‘Finishing tool’ path button, I went down the list of settings with the same values apart from:
TOOL: Fablab 5mm 2 flute preset
| Setting | Value |
|---|---|
| Stepover | 0.5mm (or 10%) |
| Area Machine Strategy | Offset |
Once calculated, the paths can be seen in animation using the ‘Animation’ tool, underneath the path tools.
When you click ‘Save tool paths’, this should include both tool paths and in the .SBP file format for the Shopbot.
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Prepare the shopbot
[For a more detailed description see Week 7]
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Open the ‘Shopbot’ program.
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Press the ‘X/Y’ button to return the milling head to home.
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Check the milling bit is extending from the collette far enough to mill the bottom of the model.
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Move the milling bit to the ‘X/Y’ of the piece of wax. Mark it as the new 0,0 through [MENU] > [Zero] > [Zero 2 axes (X & Y)]
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Move the Milling bit over the lowest part of the wax block and Zero the Z axis.
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Do final safety checks around the machine.
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Run job
Load in the .SBP file, insert and turn the key on the spindle control. Check the Spindle control box is set to 6000 revolutions per minute (manually). Wait for the spindle to run up to that speed and then press ‘Start’.
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Cast Moulds
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Measure volume / weight of water
I poured water into both sides of the moulds and emptied it into a mixing cup that was big enough to handle it. It came to 104gm. This would mean I need 52 gm of both component A and B.
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Prep mould
I tried to scrape any excess wax that hadn’t come loose already with a small flat head screw driver. I also ran it around the edges of the positive to ‘sharpen’ the edges where they meet the bottom of the mould.
I sprayed some Universal mould release into the moulds and wiped it with a brush to make sure that the layer was even and reached all the corners and tight spots. I left it to dry for 30 mins as the instructions suggest.
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De-gassing the material
As others had used the same silicon moulding material as I was going to and had ended up with some small bubbles in their mould, I decided to de-gas my material even though it said it wasn’t necessary. From previous experience de-gassing silicone, I was expecting to see something like the geothermal mud pits when I applied the vacuum. I was disappointed. just small bubbles slowly reaching the top. I did this for a few minutes until the bubbles reduced in size and frequency.
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Pour Moulds
I poured the silicone into the wax moulds slowly, making sure that i pushed some material into the corners and holes with a mixing stick. As any bubbles came up i popped them with the mixing stick. I alternated pouring some material into either mould to give it time to spread out a little and judge the amount of material i still needed to add. I continued this until the positive features were covered by the level of silicone.
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Cure Moulds
The data sheet gave a value of 6 hours for the material to cure. So I left it over night.
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De-Moulding
This was a little tricky as the silicone was a tight fit and had to nudge, prise and poke to it to release the vacuum between it and the wax. Then it just popped out. The casting had gone well, just the odd little bubble in the material, and it had retained all the detail from the wax. Bad parts as well.
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Finishing mould
Just some trimming of the thin edges, and tidying up the edges so that every side looked square.
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Casting proper
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Prep moulds
This consisted of trimming any excess material from the casting and making the side and edges as straight as possible. Clean the mould of any wax or residue from the casting.
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Measuring needed material
I did the same trick as above with water to find the volume of material needed. At 1:1 A to B components that meant 10 grams each.
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Add mould release
A quick spray of mould release and a brush to get an even layer in all angles. Leaving it to dry for 30 mins or thereabouts.
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Pouring
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This material (Flex 60) has a pot life of 2.5 minutes and turns to a thick consistency very quickly, so pouring was only possible at the start. I scooped the material in and smeared it into the moulds. Closing the mould together quickly, some of the material leaked out so I taped the sides shut, and held it together upside down in the hope any air bubbles will rise to the top through the spout opening. this of course was all done in a panic as the seconds ticked by and the material started to thicken. I placed it on its side and applied pressure on the top to squeezed the material back into the cavities as much as possible. Then I left it for 20 minutes.
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De-moulding
This was easy thanks to the mould release. The casting had not gone too well, big air bubbles in the interior of the material, but it had retained all the detail from the mould. Bad parts as well. The piece was easy to handle with no stickiness or residue, so I started to work on finishing it.
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Curing of the casting proper
The data sheet said it would reach full cure in 6 hours.
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Finishing cast
There wasn’t too much flashing that had seeped out of the sides of the cavity. Only the spout and the breather hole needed some effort to cut off excess material.
I also tried to cast with a harder material to see if the results were also as successful. I tried with ‘Smooth-cast 305’ a soft medium set plastic, with a pot-life of 30 minutes and cure time of 6 hours.
The material got really warm when mixed and set very quickly once it had started changing from a liquid. I poured it in to the mould which i had supported and held together with tape. It acted differently in the mould from the ‘Flex-60’. It poured nicely, but then different areas in the mould started to set. Causing it to expand in some places and shrink in others. The finish also dimpled all over. Not as accurate a cast as the ‘Flex-60’ rubber, but easier to work on and finish with tools.
What I should’ve done
Bigger model
Like Loes, I had a model that was symmetrical on both sides. I could’ve made my hammer model bigger to take up the whole block of wax and cast it twice to get both sides of the mould.
Extra registration point
One side was lacking space for a registration point that would’ve held the mould together better. My original design would’ve done this if i had got the corners right. But the posts were a last minute adjustment.
Milling speed should’ve been slower
We were told that the 50 mm/s milling speed was too fast and probably cause the strange areas of milling in the wax mould.
Extra material to cast the moulds
The mould was very flexible, having a thicker mould by using more material could’ve supported the mould better and stopped casting material seep through gaps.
Picked other materials to use for casting
The lack of pot life and behaviour of the materials I used for casting made working with them more difficult. The Flex-60 I should’ve done minimal mixing and just poured it into a more rigid mould to allow time for the air to get out. The ‘SMooth-cast 305’ soft plastic, left a dimpled finish, and expanded and shrank in different places in the mould.
Mistakes & Issues
Making a positive mould when it should be negative.
After making the positive of my model, I followed a ‘making a two part mould’ tutorial for Fusion360 and thought i had a finished file for milling. The i realised I had actually made the negative of the mould that i would make in the first casting.
I shouldn’t have cut the model out of a block, splitting it in two and placing it side by side.
Square edges
Whilst viewing my model and the tool paths in vCurve I noticed the nice square edges of my registration parts were either rounded in the parts cut into the wax, or had a tapered edge when in relief. This is due to the mill bit being round. Unless we use a finer mill bit in extra runs this will always make press fitting straight lines difficult in a 2 part mould. So I got rid of them and replaced them with posts and holes of a larger diameter of the milling bit.
Diameter of the mill bit in the design
I also noticed that the milling bit couldn’t get around the model properly to cut the spout i wanted. This again was due to the diameter of the milling bit not being able to get around the model properly. I increased the separation between the boundary wall and the model to accommodate this (I scaled the model ;)).
Position of the X/Y zeroing on the Shopbot
This is not very accurate, moving the milling head is not very precise with single taps on the keyboard (I maybe not doing something right?). So this meant that i moved the mill head to a point well within the wax’s boundary. This guess was almost too much as the tool path took the cutting very close to the edge on one side. Next time i will try and align the centre of the mill bit over the corner as much as possible whilst staying inside the boundary. I wrapped that edge with tape to give it more structural stability and stop any material flowing out of the mould.
The milling was a little off in some places
A couple of areas in the milled wax looked like the tool paths took a little extra wax out in a couple of places :(. I have a feeling this was due to the setting for the movement of the milling head to be too fast.
One component had already began to deteriorate
The material I was going to use for the moulds came from an old package of partly-used materials. When I had weighed the bottle of component it had said 155gm including the bottle, so I though there would be at least 52gm of material still in there. Only when I tried to pour and scrape it out did I find that there was a heavy thick layer in the bottom of the bottle that couldn’t be reached. I could only get 30gm so had to change to OOMMOO moulding silicon instead.
CONCLUSION
My moulding + casting skills are a little rusty maybe, but its always good to practice with these substances and gain experience. Everyone has their favourite materials to use, and these that i’ve tried aren’t mine ;).
Although a good way to introduce Z-axis milling into an assignment, its not a technique i would use very often to make a mould for casting. There are better techniques that allow you to work the moulds easier for a better resolution than milling.
Part of a life size dolphin I helped make with Unreal.eu. Painted silicone skin over a fibre glass composite shell. Used for camera closeups.
From a professional TV + Film perspective, 3 axis milling wouldn’t have been able to make a mould for something as big as above. It would also be difficult to make the multiple parts of the mould that were needed to prevent undercutting. The settings and the method we used wouldn’t have provided the definition and fine detail needed in the final casting (finer settings and methods might be able to solve this).
So I can only see this method being used for reproducing small simple pieces in a professional setting.