Moulding... a simple method


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by Jon Picton

The modeller will often find when building a model , especially when Scratch building, that there are parts that he/she would need more than One off, Vents and Water tight Doors on model boats, Engine cowls etc on Model Aircraft, Doors and Windows on dolls houses etc, Boxes of cargo for model trucks etc, Walls and paving for Model Railways, the list is endless, this article is about producing these items simply and more importantly cheaply using readily available products.
There are several ways of producing moulds, and various materials available for moulding an item, most of these are expensive and non reusable, here I have chosen to use a reusable moulding material and a cheap readily available casting material.

MOULDING MATERIAL
Gelflex A reusable melting compound, this material is heated to around 130c and poured over the ‘plug’ of the item to be reproduced, once the item has been cast (or a number of theses) the moulding material can be cut up and reused for another mould.


Moulding material and several door frames made from the casting box on the left

CASTING MATERIAL
I use car body filler, obtained from most car factor outlets and quite cheap, this material is strong enough for most STATIC items to be produce, it can be drilled and filed etc with ease to obtain a good finish.

HOW TO…
MAKE A PLUG

First a model of the item to be reproduced has to be constructed, here I will use parts for a Model boat and parts for a Dolls House that I am currently construction, it is not a good policy to use a part manufactured by a company and I strongly advise against this, first it is illegal and secondly if you do this you are taking this manufactures livelihood away.

The ‘Plug’ is a model of the item you wish to produce, it should be made of a heat resistant material, i.e. wood, make this as accurate as you can as any defect will be reproduced in the finished article. I always give the plug several coats of sanding filler and sand down well to ensure a good finish.

Once the plug is completed it needs to be mounted in a casting box, make the box at least 1/2 inch wider all round and 1/2 inch deeper than the plug, ensure that the plug is secured to the base of the casting box so that none of the moulding material can ’creep’ under it, if this happens you will have problems removing the plug from the casting box and you may well cause damage to mould.

MAKING THE MOULD
Once the casting box is ready, spray the entire box and plug with a releasing agent or coat with release wax, cut up the moulding material into small pieces, about 1/2 inch squares and put into an old saucepan, gently heat this to melt the compound , I have found on an electric hob setting five is about right, (recommended melting temperature is 130c ) DO NOT try to melt the material to quickly as it will burn and give of an awful stench, also remember that when melting the material ensure plenty of ventilation.
Pour the melted casting material into the casting box, small air bubbles will rise to the surface, this is quite normal and I have not experienced any problems with air holes in finished moulds to date.
Once the mould has cooled it can be removed from the casting box.

CASTING
The moulding material is a two part resin product, the manufactures recommend a ‘blob’ of filler about the size of a plumb to a ‘Pea’ size amount of hardener, it will take some time for you to ‘gauge’ the amounts required for a particular casting and the amount of hardener to filler required, use a ‘pallet’ to mix on, non absorbent, such as a piece of glass or an old mirror tile, I tend to mix up a smallish amount first and to see how much it fills, the beauty of this produce is that you can always add to the casting so don't worry if you do not mix enough first time.

Left, door frame ‘plug’ centre, mould, Right mixing ‘pallet’, Above moulds etc for boat parts and casting material.

Once you have made up a mix get it into the mould as quickly as possible, depending on how much hardener you have added as to the time the material will set, this can be a matter of minutes so do not hang about and really force the mix into the mould in order to eliminate air bubbles, you will not damage the mould with a little hard pushing.

Mixing a ‘plumb’ size blob of filler to a ‘pea’ size amount of hardener


On a long object such as a door frame it is advisable to add some sort reinforcing to give the item strength , when making the door frames for the dolls house I used barbeque sticks, cut these to length and push them into the wet material and then put more casting material on top.

Depending on the ’mix’ the casting will be ready to remove from the mould in 5 to 10 minutes, it is still ’green’ at this stage, lay the casting Face down on a flat surface to ’cure’, I leave mine over night, it can then be cleaned up and imperfections removed by gently sanding down.

IMPORTANT
Once you have finished filling the mould, clean all surplus material from your tools immediately, if left to harden on these you will have real problems getting it of once set.

From Left to Right, filling the mould, adding reinforcements, mould filled….


Casting just out of the mould


Left: rough; Right: cleaned up

Plug, Mould and castings for ships vents and hatches in 1/48th scale for a Ton Class minesweeper, the vent production can be seen from rough casting through to almost finished .

   

Plug, mould and castings for ships Water tight doors, again in 1/48th scale.

© 2007, Jon Picton.