Re: Popcorn RP

From: Jim Mallos (
Date: Sat Feb 05 2000 - 17:29:13 EET

Marshall Burns wrote:

> Yes, this is called "formative fabrication." The three fundamental
> fabbing processes, additive, subtractive, and formative are explained and
> illustrated on the "What is a Fabber" page at

Marshall, that is agreed. Formative is the correct and better term.
> I would not agree with you that biological growth processes are in this
> category. Biological growth is generally a special kind of additive process,
> which we can call "accretive." This is discussed in the article at
>, where I describe
> accretive fabbing as a process in which the product grows by adding material
> to itself rather than by the action of any outside influence. In this kind
> of situation, there is no fabber distinct from the object being fabbed. The
> fabber is fabbing itself. This is how you and I, as well as oak trees and
> house cats, grow up from embryos.
> I understand why you think of this as formative, because it seems that
> the organism injests a stock of nutrients, which you then consider to have
> become part of the organism and then to undergo reorganization in order to
> join the solid mass of the body. One can certainly argue for this
> perspective. But I prefer to think of the nutrients in the stomach and in
> the bloodstream as separate from the consuming body until the molecules of
> the nutrients have been incorporated into the structural cells of the body.
> It's pretty much a semantic distinction.
> One day, technology will learn how to imitate these magical biological
> processes. When that has happened, fabbing will have merged into nanotech
> and the limitations of what we can make will have been stripped away
> incredibly.

I also do not object to biological methods being placed in what is
presently a category of their own.

> Your discussion of popping of corn is another interesting matter. That
> definitely is formative. I've never studied this process, but the way you
> describe it sounds akin to a foaming process. You are right that the
> challenge in utilizing something like this is in achieving control of the
> geometrical changes that occur.

Yes. Though precise final dimensions are not essential, versatile
control over the part's topology is essential: we will need need to be
able to create internal passageways and cleavage planes in the foam. It
is a fair and crucial question whether this can be done simply by
programming the initial locations of bubble centers.

Jim Mallos

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