how are kits formed?

A tool steel (mold) is cut by an EDM machine, from a CAD drawing. The sprue and attachments are "gates" by which the molten styrene is injected into the mold under pressure. Each cavity in the mold will represent a part. There are two stages of kit design, one is reproducing the subject at scale, and then the "kit" drawing, or assembly drawing is developed to facilitate assemblyof the model. The tool is cut to this drawing.

The mold is loaded into a press and runs so many shots in a production run. Sometimes, water is cycled through special channels in the mold to keep it at the proper temperature. Once the mold is opened, parts are "ejected" using small hydraulic or spring loaded pins built into the tool. Some parts are removed by hand by an operator. This is where you see the round indentations "ejector pin marks" that we love to fill and sand.

Sometimes, "soft tools", (less expensive non production tools) are made first to run test shots to see if the designer and the tool maker have all thier "ducks in a row" before spending the big money on "hard tooling", or production tools.

Steve

wow! thanks crockett!

The methode described above is injection molding.

There are other methods such as resin casting(resin is poured in a mold) and vac forming ( forming the kit out of a sheet of plastic by heating the sheet and sucking it over a mold)

check out this article .... http://www.internetmodeler.com/2005/june/features/prague.php

Are kits ever sold without instructions on purpose? Is the modeler ever just supposed to "figure it out"? I think it'd be a fun challenge, and I suppose, after awhile, you kind of get used to how models go together. Do any of you just toss the directions and start building? If I did it, it'd be a good way to screw up a kit and waste some money, I can do that with the directions though.

QUOTE: Originally posted by bud156 Are kits ever sold without instructions on purpose? Is the modeler ever just supposed to "figure it out"? I think it'd be a fun challenge, and I suppose, after awhile, you kind of get used to how models go together.

Some very obscure vacform/resin/short-run kits come without instruction, but most kits come with.

Before I started serious building, I did build some kits without instructions. With a single engined fighter, it can be done.
But the result weren't that good. I did not paint or decal the kits, nor did I glue all the fiddly bits on, like antenna's. However, I often attached some extra weapons, either spares or schratch build from sprue!

I wouldn't know where all of the miniscule detailparts would go w/o instructions!
swanny- thanks for the site!

QUOTE: Originally posted by jinithith2 I wouldn't know where all of the miniscule detailparts would go w/o instructions!

Those where the stuff I left off!
(just for the record, we talking about way back!)