Resin Casting 101: Part 2 - Masters of the Universe

A master is merely a term for the model that you want to reproduce. Thus can be made up from anything you desire and be as detailed (or not) as you like.

GSW, KP and UK masters

A few random things to think about with masters:

• Put as much detail as you can squeeze into the master and avoid having to add it to your castings many times later. A casting can reproduce very fine details, both good and bad - even messy blobs of glue and accidental scratches - so go buy some modeling putty and fine sandpaper!


• You will have determined from your 'design' thinking in the previous step whether you will build the master in one or many pieces. If you are making a multi-part kitset style casting - for example because of the deep undercuts in the ends, you may chose to make a KS wagon with the core as one piece and the two ends as seperate castings - you might assemble the end masters on a large piece of stiff plasticard (or in a Kato box like the UK above!) to keep things flat.


• Resin may have trouble finding its way into very narrow crevices, leaving air bubbles or partially formed details - can you compromise by widening that detail on the master.

• The variety of preformed plastic shapes and ease with which styrene can be worked make it the material of choice for many modelers.


• Sizeable undercuts may cause your rubber mold to tear when you remove the master or resin castings. Can the undercuts be minimised? Can you bevel the edges? Should you go multipart?


• If adding fine wire details – e.g. handrails, container door rodding etc, ensure there is a good solid join by coating it with thin glue. Otherwise, if there are gaps, the rubber will seep under the wire and the detail may not show consistently in your castings. An alternative for handrails is to put locating dimples into the master and then later drill out the casting for freestanding wire handrails.


• Undercuts , horizontal ribbing and things that will form holes in the mold (XP roof vents)may trap air during later casting, leading to air bubbles. Can these features be minimised?

For the next few posts we'll put aside the more complex forms of molds and use simple one piece examples for the creation of container flat wagons and box wagons.

A few comments on 'Design' decisions made for the masters presented here. The XP has a roof overhang that would be deep in the mold (when upside down) where it was likely to cause problems - I placed a superthin strip of unprototypical (and crooked) plasticard under the lip and beveled it slightly by dragging the edge of a knife blade along it with the hope of making the master and castings more easily removeable from the mold. Alternatively I could have made it flusher with the walls (as I did on the ends). As feared, the roof vents are a source of air bubbles that need to be eradicated during casting, but there's not much that can be done about that.

The only challenge with the GSW and GSX was the fine wire - see the handrails comment above. It has no air bubble problems at all, however the KP gets loads of bubbles in the horizontal door ribs unless you're careful when pouring the resin. Both use 'roofing styrene' as a big part of their construction (Kp ends)

The UK is a pretty simple master made up of flat and rectangular styrene sections. Details such as handbrake supports and ferry fie down hooks were simulated and these look nice on the castings - they don't take too long to do on the master and once they're done you can enjoy them on every subsequent casting. I spent a lot of time during the 'Design' phase weighing up the pros and cons of making a multipiece mold for the prototypical steletonal see-through underframe with lots of angle bracing. In the end I made mine 'solid' to enable a nice stiff one-piece casting to be easily removed from a mold. The solid box section also allows me to embed weight into the castings. More on that in a later episode. On the finished models I paint everything black and then pick out the angles in a lighter colour, and even when your eye is trackside, I don't think the solid look detracts from the models. Life is full of compromises!

Various lumps of styrene, wire and plastic assembled into a master

Legal disclaimer: Obviously you shouldn’t make straight copies of commercial kits or the models of others.