Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

CAD or physical, 3-up or actual size isn't the issue.

The main issue is undercuts. See this blog article (from Steve Buddle who now designs for GW) for a proper explanation, but basically the silicone moulds for resin and metal models are flexible, so minor undercuts aren't a problem as the mould flexes when you remove the models. Large undercuts can cause damage to the moulds or miniatures, which is why a lot of one-piece models will have pouches, holsters, clothing, etc, filling in gaps. Moulds for polystyrene models, however, are made from metal, and can't flex. This means you can't have any undercuts at all. If you try and make a plastic version of a metal model, you'll need to fill in all the undercuts. For any old-timers here, look at the painting guides for old GW games like 1st edition Space Hulk, Space Crusade, Heroquest or Advanced Heroquest. The painted models on the boxes will be the metal or resin prototypes, which are more detailed than (and have slight differences to) the final plastic models.

One minor example of this is the studs on the left shoulder of mk6 Marine armour. On a metal model, those studs will all stick straight out from the surface of the shoulder pad. On the plastic RTB01 models, they all point in the same direction, perpendicular to the plane of the mould (which makes the ones at the sides rather distorted). The same is still visible to a lesser extent on the current plastic Tactical Squad models.

This is one of the reasons that GW's new plastic models come in so many odd-shaped bits - it's to allow for details in all directions on the final assembled model. They can do this because the CAD/CAM software automatically works out the required cuts rather than relying on the designer or mould maker.

The softer plastic such as the PVC material used in Reaper Bones models and all sorts of modern board games, doesn't have this problem to the same extent as that plastic will deform to allow it to be removed from the mould, so it's easier to take models sculpted for metal or resin and convert them to this material (which is how Reaper started out with Bones).

IIRC, the resin models are also designed using CAD, and then master models are 3D printed. Those printed models are then used in place of "greens" to create master and production moulds as has always been done

Finecast isn't a material (I've had plenty of Forge World models that feel identical to Finecast), it's a manufacturing process. Essentially, metal models are spin-cast (the moulds are spun at high speed; molten metal is poured in the centre then centrifugal force forces it outwards through the mould cavities. This forces it into the extremities better than relying on gravity and fluid pressure alone) while resin is vacuum-cast (the moulds are filled from the top - the big wedges that Forge World parts come attached to are the pour funnels - and then placed in a vacuum chamber one or more times to "suck" out any bubbles of gas in the liquid resin).

Finecast was an attempt to spin-cast resin models. After all, GW had a load of spin-casting machines they suddenly weren't using, so it was worth a try. The extra sprue and gates and "shards" of resin are apparently needed to help the resin flow into the extremities properly. Whether they've got better at it over the last few years or if they've abandoned the process and gone back to something more traditional now that the number of ex-metal models in the catalogue has reduced I don't know.