How to make a copy of a (lost) part

Article by Rob Haelterman - heman_148(at)hotmail(dot)com

Imagine the following situation: you have just bought an expensive, high-quality kit; to your dismay you discover that a part is missing (either it wasn't there in the first place, or the carpet monster got to it before you did). What do you do?
There are some options:
1. you buy a second kit;
2. you try to find a diorama setting, e.g. maintenance, that doesn't require the part;
3. you contact the retailer/manufacturer for a replacement part.

Suppose now that you go for option 3. After a while you discover that the customer service the retailer/manufacturer pretends to offer is not what it is claimed to be. Then what ?

Here is a simple solution, assuming you have access to a copy of the missing part. (This can be either because this part should be included n times in this kit (n > 1), but you only have it n-1 times, or because a friendly modeler trusts you to borrow his part.)

In the example here, I am trying to make a copy of the sprocket mount of a Tiger I that was missing in a plastic kit from an unspecified Chinese manufacturer, but didn't send the replacement part that was promised after sending an email. I assumed that the left and right mount were (near) identical, so I decided to make a copy of the other mount. I first made a cast using regular DIY silicone. After a day or two I removed the plastic part (which should be fine after this ordeal). In the meantime I had taken a small jar, filled it with pieces of styrene sprue and Methylethylketone (MEK). After a day or two, the plastic has dissolved into a slimy paste, a bit like Mr Surfacer. (Adjust the amount of sprue to have a viscous mix.)

Having removed the original part (quite important that you do), I now poured the mixture in the cast. After it has dried, the mixture will have shrunk substantially, so you will need to top up. (Do all this in well-ventilated area: MEK is highly toxic.) I let it dry overnight and removed the part. Depending on how much care you applied, you now have an exact copy in styrene, so easy to handle. As you can see, mine has some airbubbles, which - it seems - is unavoidable, but at least I have a new part. Some cleanup is needed on the open end of the cast.