Help with organic topographical model

[badboi]

Hi,

I have a project I am working on...

The concept is a topographical model
Something like this...but many more ridges and valleys all being very smooth
http://www.indianjournals.com/showdocument.aspx?target=publication&type=articleimage&id=ijcir-3-2-003-fig005.jpg

http://www.topodepot.com/images/contours3d.gif

the total size will be 50cm wide x 100cm long x 25cm high
I am very new to mold making, etc, so hopefully someone here can help me.

I want the end result to be a very smooth, shiny surface/solid. I am open to any material choices for now.

I have axis to a 3-axis mill which can get a very accurate surface model from wood or styrofoam....
How would you make a mold from this?
I can CNC Mill a negative of the object or the postive.

Also, how do you smooth out CNC model and what materials would be appropiate.

The lighter, the smoother, the shinier the better

thanks for any help

[WillPaq]

There's a lot of open questions still with your description, among them what your surface should look like as far as color.

If it needs to be lightweight, I would mold the prototype with silicone rubber, then slush cast the piece in resin so it is hollow, and then fill the interior with expanding foam. The resin will sand smooth and then you can finish it by spraying with automotive paint, or send it to a body shop to paint it for you and then wax it, like you would a car.

After filling the body of the cast, mount it on masonite or some other relatively thin backing to keep it rigid.

[The Forge]

The smoothness of the finished surface is dependent upon the CNC program and the material. Keep in mind that going from positive to negative is not as easy as it may seem. There are surface details that can be achieved in one direction, that will not be able to be done in the other. :)

[Andrew Werby]

Which mostly provoke more questions than answers...

Hi,

I have a project I am working on...

The concept is a topographical model
Something like this...but many more ridges and valleys all being very smooth
http://www.indianjournals.com/showdocument.aspx?target=publication&type=articleimage&id=ijcir-3-2-003-fig005.jpg

http://www.topodepot.com/images/contours3d.gif

[Those are somewhat different. Are you trying to replicate the actual topography of a specific place, or an abstract mathematical topographic concept?]

the total size will be 50cm wide x 100cm long x 25cm high
I am very new to mold making, etc, so hopefully someone here can help me.

[Why are you making a mold? How many of these do you need?]

I want the end result to be a very smooth, shiny surface/solid. I am open to any material choices for now.

I have axis to a 3-axis mill which can get a very accurate surface model from wood or styrofoam....
How would you make a mold from this?
I can CNC Mill a negative of the object or the postive.

[Have you actually done this yet? Have you made a model in the computer that describes your surface? I'd suggest starting smaller, and working up to this fairly large piece. Mistakes are less painful when they're small. You can use the small test parts to do some trials of proposed techniques.]

Also, how do you smooth out CNC model and what materials would be appropiate.

[The CNC can carve the part quickly and roughly, or slowly and smoother. Depending on what you're using, the techniques used will differ somewhat. Wood, for instance, can be sanded. Styrofoam doesn't respond well to sanding. There are coatings that work on wood that don't work on Styrofoam. You really need to decide exactly what you're trying to do and with what, then we can give you specific tips on how to do it.]


The lighter, the smoother, the shinier the better

thanks for any help

[You seem to be thinking of the surface first, and everything else second. But I think you really need to decide what you're actually going to carve (or cast), and then worry about how to finish it.]

Andrew Werby
www.computersculpture.com

[vern terry]

Hi,

I would use signage urethane foam to cnc my positive. Then use rifflers, files, 80 grit sandpaper to 150 grit to smooth out the topo relief forms. Then apply a spackel coat and fine sand. Shoot it with grey primer to check for holidays (divits) and spackle and sand those voids. shoot another coat of grey primer and paint with my final color with lacquer (fast drying). Make sure the primer and lacquer are compatible!