Fabricating complex shapes: A sugar chain

Monday, July 30 2007 @ 05:48 AM PDT

Contributed by Windell

One of the hallmarks of rapid prototyping technologies is that they are additive processes, where material is incrementally added to a form. This makes it practical to make complex shapes that cannot be efficiently manufactured by traditional subtractive processes, such as CNC milling, where material is cut away from a block to make an object.
Consider, for example, a chain of connected links. While skilled whittlers can indeed carve a chain out of a single piece of wood, it's a labor intensive process that requires accessing the part from many different angles. In contrast, in an additive process it is no more difficult to make a connected chain than it is to make any other shape. To prove the point, we constructed this chain of 12 links-- using about a pound of sugar per link. (Yow!) Read on for a few build photos.

We began with the design for the completed chain, drawn in POV-Ray. Each chain link consists of two tori, cut in half, and connected by two cylinders. This gives the appearance of a stretched chain, but with a proper circuilar cross-section at every point. The twelve links are arrange with six lying flat and six arranged vertically.

The next step is to slice the object into a set of 2D images. We have previously detailed the method that we are using, which essentially consists of computing the intersection of our object with a thin horizontal box, the thickness of which is matched to the thickness of our printing layers. For this large object, the layers are 1/8" (3.2 mm) thick.

Chain model

The animation here shows what a representative set of the slices look like, as we build up the object. (Not all layers are shown).

When we first start to build up the chain, we are only printing the lowest part of the six chain links that are vertically oriented; it's hard to see from the pattern of melted sugar alone how this will turn into a chain.

In the middle section of the chain, where we are printing parts of all twelve links, it is a little more obvious what we are printing.
One thing to note is that the loose "horizontal" links are suspended by the loose print medium (sugar) in the print bed. This is in contrast to some other fabrication technologies which require a separate support matrix to be built alongside the actual desired obect.

And there we have it!

MetaBlog links for this story: [ del.icio.us | technorati ]
Technorati tags: POV-Ray, fabrication, howto, candyfab, 3d printing, software, slicing, chain, sugar

Comments (8)

The CandyFab Project
http://www.candyfab.org/article.php/complexshapes

	We began with the design for the completed chain, drawn in POV-Ray. Each chain link consists of two tori, cut in half, and connected by two cylinders. This gives the appearance of a stretched chain, but with a proper circuilar cross-section at every point. The twelve links are arrange with six lying flat and six arranged vertically.
The next step is to slice the object into a set of 2D images. We have previously detailed the method that we are using, which essentially consists of computing the intersection of our object with a thin horizontal box, the thickness of which is matched to the thickness of our printing layers. For this large object, the layers are 1/8" (3.2 mm) thick.
	The animation here shows what a representative set of the slices look like, as we build up the object. (Not all layers are shown).

When we first start to build up the chain, we are only printing the lowest part of the six chain links that are vertically oriented; it's hard to see from the pattern of melted sugar alone how this will turn into a chain.

In the middle section of the chain, where we are printing parts of all twelve links, it is a little more obvious what we are printing. One thing to note is that the loose "horizontal" links are suspended by the loose print medium (sugar) in the print bed. This is in contrast to some other fabrication technologies which require a separate support matrix to be built alongside the actual desired obect.
	And there we have it!