Sunday, November 11, 2007


Thoughts on printing at ambient temperatures

I hit a technical problem back in September and you haven't heard much from me since then. I've been able to print in HDPE and am well on my way towards sorting out the problems with using brushed gearmotors to run both the extruder and the Cartesian positioning system of Tommelise. I'm publishing in the main blog rather than the builder's blog this time in that the issues that I am addressing impact on both Darwin and the various repstrap machines that are abuilding.

As you are all aware by now, I am sure, HDPE and to a lesser extent CAPA tend to curl when extruded at ambient temperatures.

This curling tends to happen at corners when the aspect ratio of the object being printed approaches 1. When you have long objects you tend to get curling in the plane of the longest dimension. Nophead published some really compelling photos of this effect over in the builders' blog last month.

I got very discouraged about the warpage issue and resolved not to share my misery with the rest of you if and until I came up with a viable solution to the problem.

(Read the full story)

To inject a bit of polymer science: The shrinkage you see is mostly due to crystallization, something which polystyrene (whether or not it's been modified to form ABS) isn't subject to.

I think a big part of the reason for delamination is that the part was completely cool when you began in the morning, so that the stresses were highest between the old material and the new.

You might try LDPE. The properties aren't as good, unfortunately, but at least it won't shrink as much during melting. Filled polymer will also shrink much less.

Built-in stresses can be annoying, but clever design can make use of them...tempered glass comes to mind, for instance.
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