Scratch-Building - Another Project - Working with Expanded Polystyrene Foam?

[Mako]

I've got another project I'm considering as well - again, another spacecraft build, but this time using the Rigid, Expanded Polystyrene Foam.

Seems best for this other design, to just go with a solid piece of foam, and then cut, carve, file, and sand to shape, as needed.

I know I can use basic tools for this, e.g. box-cutters, serrated knives, files, sandpaper, sure-form planes, rasps, etc., etc..

However, I could use some tips on what grit sandpaper to use for rough-shaping, and then smoothing/finishing, once that's done.

I know to wear eye protection, and a mask, to prevent inhaling the dust/shavings.

Also, any decent tips on making the model symmetrical too?

That seems like a good challenge, when building something like this from scratch.  Was thinking about using some cardboard cutouts, and/or templates, in order to check the overall symmetry, from time to time.

Thoughts?

[Wirelizard]

80 grit sandpaper works nicely for rough shaping, although be aware it can take foam off shockingly fast sometimes! It can also tear the foam, so starting with 120 grit might be better if you're going for an exact overall shape. Most of what I've used styrofoam insulation board for is just hills and other scenery where exact shape isn't as important.

120, 180, or 200 grit for finer shaping.

Cutouts/templates/etc for symmetry and consistent shaping should work nicely.

I think the main thing would be to take it slow, especially with the first couple of shapes, and be prepared to cut and patch if needed.

[Mako]

Thanks for the reply, and tips.

I really appreciate it.

[Johnnytodd]

Also, any decent tips on making the model symmetrical too?

Start by drawing registration lines dividing your model in halves  (like cross hairs).  As you remove material keep redrawing those lines.  Remove small amounts at a time.  Also buy a caliper tool:
http://www.globalindustrial.com/p/tools/test-measurement/calipers-dial/general174-dial-caliper-142?infoParam.campaignId=T9F&gclid=CJ_zi_ug3tQCFZtWDQod76EBcg