Subject: Re: Foam patterns?

From: [email-masked] (Greg Pettengill)
Date: Thu, 12 Jan 1995 04:54:56 GMT

In article <[email-masked]>, [email-masked] (JOHN ABERCROMBIE) says:
>
>What type of foam should I use? What's the best way to cut/shape the 
>foam? Can flat pieces of foam be "glued" together somehow to make more 
>complex shapes? (Could I use hot melt glue, for example?) How acceptable 
>is the surface finish from a foam pattern? In other words, can the 
>pattern be smoothed somehow? Most styrofoam (beadboard) has a very 
>porous structure.

Hot wire & heated tools are most commond, also saws work well for cutting
and shaping.

White Glue works well and is cheap. I would guess that hot melt glue would
be too hot for the styrofoam.  Let me know what happens if you try it.

You may want to try experiment with coating it with a RTV foam like REN RP 306. 

  Greg Pettengill                                  Cote'
[email-masked]                     The Fine Art of 
  (602) 375-2922                    Product Development

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From: [email-masked] (Patton M Turner)
Date: Sun, 15 Jan 1995 21:25:33 GMT

>>complex shapes? (Could I use hot melt glue, for example?) How acceptable 

Hot melt glus must not be so hot as to cause bead colapse.  These glues 
are available.

>>is the surface finish from a foam pattern? In other words, 
can 
the >>pattern be smoothed somehow? Most styrofoam (beadboard) has a very 
>>porous structure.

Production castings use blown foams, so the beads are expanded against 
the wall of the pattern, and are smoother.  I have used real dilute 
solutions of glue to improve the surface somewhat.  Hot wire and high 
speed machining produce improved surface quality also.

Blown faoms have a better finish than greensand castings.  You could 
still see the outline of the beads on the castings, unless they got a 
real long shotblast.

>You may want to try experiment with coating it with a RTV foam like REN RP 306. 

The pyrolysis products of styrene are bad enough, you might get a lot of 
cynaide compounds from expanding foam.  Make sure the area is well vented.

Pat

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From: [email-masked] (Tim Nye)
Date: Mon, 16 Jan 1995 13:58:26 GMT

I was wondering about one detail on built-up foam patterns (and since there 
is so much expertise around I though this a good time to ask).

Suppose you glue two blocks together at right angles.  How do you make a 
fillet where the pieces join?

Thanks in advance,
------------------------------------------------------------------------------
Tim Nye                            "Duct Tape: The handyman's secret weapon"
University of Waterloo                          - Steve Smith, aka Red Green

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From: [email-masked] (BrnzCaster)
Date: 16 Jan 1995 10:36:58 -0500

I use wax to make the fillet on foam patterns.

Winston

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From: [email-masked] (Patton M Turner)
Date: Sun, 22 Jan 1995 19:37:19 GMT

>I use wax to make the fillet on foam patterns.

Thats the way we did it also, though way will increase the available 
carbon for defects.