Wednesday, 14 May 2014

Frustration and Fun with Rubber and Resin!

So… I’ve been making progress and here’s my new machine

Sarah’s Simple Spin-caster

My friend at Roundhouse Engineering in Norwich (no website, so pm me if you want contact details) made the turntable from a slab of aluminium. He also made the bits that hold it onto the motor shaft, and constructed the frame to hold it all together and lift the motor off the work surface. It’s got to have plenty of air for cooling as it runs. The smaller purple unit is the ‘interrupter’ e.g. the control and tells me how many rpm it’s doing. That and the labour cost way more than the motor but I’m not telling you how much! It weighs a ton, but that’s good because it needs to be stable. 

It's now bolted to the floor and has a fence of cardboard constructed round it to stop spraying the whole workshop with a fine dusting of sticky resin!

And here’s my other machine, the vacuum chamber for degassing mixed rubber and resin before pouring it into the mould. This is the photo from the listing when I bought it as I haven't taken a pic myself.

It came with woefully inadequate instructions and I think I deformed the clear acrylic chamber but vacuuming too much, because they don’t say what it will stand or should go up to. What’s the point of a dial if I don’t know what they mean? I have emailed the suppliers pointing this out and asking for a bit more guidance. I have used this for degassing the mixed rubber. It’s great seeing the bubbles appear out of no-where and get larger and larger till they burst. Every bubble bursting is one less to cause me problems when casting!

The silicon rubber I bought is ‘Platinum cure’. It’s the most expensive but gives least shrinkage. The other sort is ‘tin cure’. You mix (accurately) equal amounts together. You can get another sort which is called 'Condesation cure' and can be used in wet situations. I want to cast a fish for a friend (that's another story entirely!) but the some guy I spoke to said you can't use this kind in the same environment as the other kinds so maybe I'll re-think that...

The rubber and resin comes in two parts. One tub is yellow and the other blue. I went out and bought loads of containers with different coloured lids so I can make sure I don’t muddle up the utensils used for each tub. You have about 15 minutes with this to mix and degas and have completed the pouring, which is a challenge but not as bad as the resin where you have about 5 minutes. The resin is a polyurethane one. THis is stronger I believe, than polyester resins. Both the resin and rubber are ‘prototyping quality’ of materials, e.g. they cost loads but should give excellent results. Got them from Moldlife in Bury St Edmunds, Suffolk ( where they give excellent advice too.

The resin and rubber are so expensive that I needed to know how many times I could make a complete mold before I’d have to shell out and buy some more, so I did some maths. (Actually felt rather pleased with myself as maths was never my strong point.) I worked out the volume of rubber and the volume of the area I thought I would need for a complete mold. I divided the first by the second, and reckon I can get make 4 whole molds from the 2 kilo kit I bought. I may find that I need more space than I anticipated, now I have started experimenting…
I have been thinking SO hard about how to go about making the molds… You have to think about the direction the viscous liquids flow in, both for the moldmaking and the casting. These are not the same directions because one is the inverse of the other! And you have to think about the fact that you turn the mold over while making it too, which further complicates things. I think...

I thought I was really faffing about  and prevaricating, but I am glad to have thought about it so much because there have been a few moments of realisation; ‘Ohhhhh I see… I can’t do it like that… I’ll have to do it another way…’ I got a load of Twelvemo part ready t pour rubber on, and suddenly thought that it would be a good idea to try embedding a single piece of a less good Twelvemo, you know, just in case I got the wrong rubber and it sets like concrete around the parts… That kind of thing.

It’s so slow, at the moment.... Every time I pour rubber molds I have to wait about 24 hours to be sure it is properly fully cured and set. It’s also cooler down in the shed which makes it take longer…. Patience, patience… (I am writing this to put off prizing apart the cast, which is the first one I will pour resin into and actually see what happens. I am scared the resin will be too thick, and I’ll have to make clunky great holes for it to flow through…  

Here are a few shots that show my progress.  The first casts were a bit dispiriting.... 

But I was not down-hearted! Noooo! 
  It took me a while to realise all the variables that can be adjusted. Mostly it's in the mold making where you have to think really hard about how the liquids pour and flow at various parts of the process: The silicone rubber to make the molds, the resin inside the moulds, the air vents to allow any bubbles to escape, the vacuum chamber (shockingly bad instructions), the spin caster and the speed at which it revolves, and the amount the mould is clamped down is crucial too. Too loose and the resin get in between the layers of the mould halves, too tight and the mould is deformed in the process.  

And I have devised a way to warm the moulds once resin has been poured in as this helps make the pieces stronger. I'm using a box lined with blankets, warmed with three very hot water bottles. This does help loads, partly because the warmth makes the resin less thick and viscous and it goes into all the spaces of the moulds better.


I have been making this is three moulds. One for the body and heard parts, one for  the larger bits of arms and legs, and one for all the really smal parts (neck wrist, ankles, hands, feet etc. Haven't got photos of all the moulds. Sorry.

This one above was one that didn't work out right.  Strangely the first one to give anything like a reasonable result was the one with the smallest parts in, shown below. This was encouraging, as last time I tried casting Twelvemo FIgures myself about 15 years ago, those were the parts I had the most trouble with. 

It's a bit of a jump, admittedly, from the photos above to the next photos. The figure is very far from perfect and every part is flawed to some extent. It's partly holding it's position by virtue of tiny bits of Blu-tac inside a few of the joints, but what is encouraging is that if I can make them like this then I can make them better. I'm learning loads rather fast! 

All parts for one figure need to be made from one single mould, so that is next, bringing all that I have learned together in one new mould. Three separate moulds means three separate loads of prepping, mixing, pouring spinning, de-moulding. This all takes quite a bit of time and I really need to be able to make a figure in one single go.  
I was trying to be very economical with my use of the rubber for mould making but now I know better what I am doing I also know that more rubber and space around every part helps the moulds keep their shape when getting clamped in the machine and when spinning. I'm all out of my first lot of rubber and resin, but next time I order I'll get a resin with a longer 'pot life' (longer time before it sets too much to flow in the mould).

The resin mix doesn't give very consistent colour so far... Sometimes it is more translucent than others. I don't really mind if one whole figure is a bit paler or brighter white than others but it would be good to have every figure a consistent colour within itself. 

The resin colour can be changed using oil paints I am told.... That's nice and simple but I think I'll try just using some proper powder pigment, as that's what oil paint is coloured with and I have some of this in various earthy hues. In the very beginning I wanted a pure white Twelvemo. I wanted the figure white to go in a book with white pages, and a hole cut out to house the figure. The idea was to have replaced text and image with a blank canvas of a human form, that the handler/user could project their own narrative on. At the time I couldn't get resin in pure white. Now I have got it I want to change the colour! (I might still make the book thing though. It's still a quite cool idea.)

After getting this figure put together yesterday I was pretty chuffed, then I awoke this morning to a message from someone via Etsy asking if there was a waiting list for ordering Twelvemo Figures, which is very encouraging.  

I'd tweet about this if I was any good at Twitter, but look at me! 140 characters? You're joking aren't you? If anyone else wants to tweet Twelvemo's slow journey into public life please feel free to do so and point them in this direction.  So... Watch this space as I'll be back in a week or two with more and better news!


  1. Congratulations on the Great Progress which you have made with Twelmo! I am so happy for you!

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