Wednesday, 15 March 2017

Casting: The Kit List!

...and so, after three trying months of sculpting an all together far too small a pile of Polish vehicles we come at last to the most testing of sequences in a chain of events that will ultimately lead me to being able to field the Polish 10th Motorised Cavalry Brigade; The Black Brigade in my Flames of War games... the actual mold making and casting of all of these lovely little vehicles that nobody competently makes!

So, as Im going to talk you all through my trials and tribulations that I suffer I thought it may be a good idea to provide a kit list that I have put together and explain my choices... kind of setting off on the right foot so to speak...

The Kit! (so far)

Well I guess the first thing that I would have to say is that if you are the kind of ne'er say die daredevil that wants to embark on a cast-up-your-own-miniatures mini adventure (car not included!) then you should really take stock of things because this is in fact no mini adventure at all... and not cheap either!

Check out the picture above and you will see all of the gear that I have decided is necessary to do this. It even looks like its a kick in the financial happy sacks!

However, when all is said and done I anticipate that there will be a certain gloating pleasure in completing my aims this year! :D

Fortunately where this is all concerned I had a leg up in 2015 when a Chinese manufacturer screwed up a piece of film equipment that I had ordered and I was left with a nice sum in the bank wondering what to do with it. I decided to purchase a vacuum pump from an Ebay supplier which spent a year in mothballs while I finished up other project.

The Vacuum Pump - £220

The Vacuum Pump kit

Now these things are not generally cheap BUT this particular ebay supplier (http://www.ebay.co.uk/usr/trevoralandixon2010) has been putting these kits together and selling them for quite a while at very reasonable costs. I chose a kit that had the largest vacuum cylinder that I could find as I have a French Indochina 'Dinassaut' project hoving into view next year and these are items I am intending to sell so I need a cylinder that can fit the molds for the boats.

Why use a vacuum pump? Well there are two reasons actually. 

Firstly when you are mixing up your silicon rubber ready for the mold to be made air bubbles will become trapped in the mixture due to its high viscosity. On drying some of these air bubbles will lay against the sides of your product leading to resin bubbles becoming a part of your final piece... and believe me, I know from previous experience of buying somebody elses attempts that it takes a LOT of work to disguise these errors. Its easier just to eliminate them straight from the get go. Before you pour your silicon over the prototype stick the mixture into the vacuum chamber to extract the air from it... then pour!

Secondly if anybody has done any home casting before, one of the probable flaws in your produce will be all of the resin holes and cavities that plague your vehicles. This is an inherent problem with drop casting and is caused by bubbles of air being trapped against the sides and undercuts of the things you are trying to make. Removing the air from a casting environment reduces the size of these cavities to almost negligible sizes. Placing new casts into a vacuum pump improves the quality dramatically. The higher the viscosity of your resin, then the greater the improvement in quality of the final cast.

The Silicone Rubber - £81.95 (2kg Kit including Taxes and Shipping)


Make no mistake. Casting is expensive. A 2kg kit is deceptively small due to the weight of the component parts and the Silicon is the most expensive part of the casting materials (the vacuum pump not included of course). It is however an unavoidable expense depending the scale of the operation you want to run with.

There are two main types of Silicon Rubbers to be considered and that it Addition Cured and Condensation Cured. Each will give you a silicon rubber mold but achieve them in different ways both of which however are classified as Room Temperature Vulcanisation (it creates its own heat internally through chemical reaction).

There are a bewildering array of Silicon Rubbers on the market which we can use, for a vast range of techniques but for me I only envisage a single operational method, and thats dropcasting small scale military vehicles. With that in mind the two post important elements that I thought I needed to study up on are its elasticity and its durability.

After reading around the subject for quite a while I came across TOMPS Addition Cure RTV Silicon Rubber Viscolo 13. Its actually another organisations product but one which TOMPS have rebranded as their own and the 13 relates to its position on the Shore A hardness scale... meaning its soft! Damn soft! Owing to the degree of detail and undercutting I will likely need to take into consideration (mainly because of my tanks... look no further than my 10TP) this silicon rubber compound is widely lauded as resisting Polyurethane resins (used for the actual casting) better than any other and outlasts all condensation cured silicons and many, if not all addition cured silicon rubbers. Nice!

Testing has indicated that the molds can sustain up to three times more 'pulls' than other silicon rubbers, can usually be used without a mold release substance and can stand a far higher degree of deformation returning to its original shape...

To me this one seemed like a winner! Not the cheapest but certainly sounded like the most forgiving for what I am aiming to do. 

When I start complex projects I dont like to cut corners  because it creates bad habits. I like to get it right the first time, where possible. By buying this option I was hoping that I would achieve this!

The Polyurethane Resin - £37.04 (including Taxes and Shipping - bought off of ebay.uk)


If you get your mold making practises correct then the next big hurdle is actually the casting of the miniatures themselves.

Just as there is with the Silicon Rubbers there is also a vast array of resins to choose from. Polyester resins are the cheaper option but for relative values where casting toy vehicles is concerned then you shouldn't really look any further afield than your Polyurethane Resins.

Polyurethan Resin is easy to use and because of this it is a popular choice for anybody venturing into home casting and craft uses. It is usually opaque when cured and sets quickly with a 'pot life' of between 3-15 minutes and ready to demould after about 30 minutes. Its usually mixed by volume which means its an easier option than those mixed by weight (due to different Specific Mass' of parts A and parts B for some choices). Its proven to be less brittle than Polyester Resins and easier to work with once cured. Perhaps the greatest benefit to us model makers is that the viscosity available is much MUCH lower with Polyurethane Resins which means you can do slush casting easier and make sure that none of the tiny detailed areas get missed.

The TOMPS Fast Cast Polyurethane Resin that I chose is specially formulated to cure in thin sections of less than 1mm which other resins would struggle massively with due to the requirement for chemically driven heat in the curing process...

This resin is, believe it or not, one of the cheapest out there, which I think beggars belief when you understand the qualities that it brings to the table (so to speak). It has an uber viscosity of around 40-50cps which means essentially that when first mixed it has the consistency of milk... there is no detail that this will miss! It has a pot life of 3 to 4 minutes so you need to be quick BUT with a consistency of milk the need to degass before pouring should be unnecessary. We will see about this. Best of all perhaps is that, once cured, it has a hardness rating of Shore D 72... which means its transformed into granite! Its hardness rating that ice climbing boots soles are rated to. 

This is one attractive product!

The Release Agent - £20.99 (ordered off of ebay.uk)


When creating molds or casting from pre-existing molds it can sometimes be an advantage to make extraction of prototypes or new casts possible. Technically it shouldn't be necessary with the products that I am using but I decided that it is better to be safe than sorry and decided that a Release Agent would be better to hand than not having it at all and so it made my list!

Mold Containment Walls - £19.87 (including taxes and shipping. Ordered from ebay.uk)


When creating your molds you need to use a material to create the walls within which the molds will be poured. If using a really soft silicon rubber it will also help to have the retaining walls in place to prevent mold deformation if you aren't flush with your silicon (use a lot of it to create really wide molds). I opted to go for lego as it means I am able to create molds of differing sizes and shapes.

Scaled Mixing Pots - £11.68 (including taxes and shipping. Bought from Ebay.uk)


Mixing silicon rubbers require scaled measuring beakers which can be cleaned afterwards and then reused. I bought a large one as well so that I can degass the silicon mixture before pouring as well. Leftover silicon can be left to cure in these beakers and then easily peeled off.


Hot Glue Gun - £10.99 (including taxes and shipping. Bought from Ebay.uk)


The Mold Retaining Walls need to be fixed securely to the Casting Baseboards in such a way that leakage under the Mold Retaining Walls. This can be done by using a Hot Glue Gun to seal on the inside of the wall edge that lines the Baseboard. Nice and cheap as well!

Casting Baseboards - £6.05 (including taxes and shipping. Bought from Ebay.uk)


Baseboards are what your molds will actually be made on. You need to have a very healthy border around the mold retaining walls and they need to be durable as you are likely to use them over again. I chose MDF boards that I ordered off of Ebay.

Disposable Mixing Cups - £2.42 (including taxes and shipping. Bought from Ebay.uk)


Whereas the Silicon Rubber thats mixed up can be easily peeled off, the Polyurethan Resin that is mixed up and cured cannot. Once cured the mixing pot is essentially unusable and therefore needs to be discarded. The cheapest option out there is the disposable plastic cups which can be picked up off of ebay at a VERY reasonable price!

Electronic Kitchen Scales - £6.89 (including taxes and shipping. Bought from Ebay.uk) 


Absolutely vital to have due to the necessity to mixing the Polyurethane Resin by weight as opposed to volume due to the differing Specific Masses of the parts A and parts B that need to be mixed up and the requirement of accuracy that mixing these parts requires if a good outcome is to be expected. 

Disposable Graduated Pipettes - £3.25 (including taxes and shipping. Bought from Ebay.uk) 


Disposable plastic pipettes may be required whenever you want to mix up small volumes of Polyurethane Resins and they can be found on ebay at very reasonable prices.

Paintbrushes - £2.29 (including taxes and shipping. Bought from Ebay.uk) 


Two reasons to by brushes! Firstly any spilled Silicon Rubber can be cleaned up using white spirits on your brushes and secondly when making moulds that require a LOT of detail it can sometimes be advisable to paint the silicon rubber onto the prototype using brushes to create what is called a 'Detail Coat'. This can guarantee that none of those fine details are missed!

Mixing Spatulas - £2.95 (including taxes and shipping. Bought from Ebay.uk) 


When mixing your parts of the silicon rubber (and your PU Resin) thorough mixing is an absolute necessity so having decent mixing spatulas is advisable. With your Silicon Rubber these can be reused so decent spatulas are advisable!

White Spirits - £3.50 (including taxes and shipping. Bought from Ebay.uk) 


White spirits should be considered a necessity when embarking on casting due to the fact that the materials that you are using can be cleaned up using white spirits... and you can use it to clean the brushes that are being used on your detail coat!

there are few more bits that I've ordered to add to my kit list that I havent received yet and  which I already own but forgot to add to the photos which are:

A spirit level to make sure that the molds are curing flat.

A pouring funnel to make sure I can get my Pump Oil into the Vacuum Pump without flooding my work space

Giant Disposable Syringes so that I can draw enough of the Parts A and B for the Silicon Rubber to cure properly.

So there we have it guys, a complete kit list! Now lets see if I can actually use it without the need for summoning Great Britain's emergency services!

Nothing more to say on this other than...

Fix Bayonets!



2 comments:

  1. Wow .... i never thought it would be soooo much work bro, and as for the cost ��..... you have put a lot of effort into this so fat and hope its all worth it mate �� Ps lol at hit in the financial happy sacks ��

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    Replies
    1. Well you know what they say Johnnie; practise makes perfect... and apparently very poor as well! LOL

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