Sunday, October 23, 2011

Source Code and Documentation

First, I want to say that I’ve open-sourced LcAlg, my program for generating laser-cut polygonal sculptures from 3d models. There’s a link a little bit farther down on the page if that’s what you came here for.

Second, the majority of this post will be about an interesting method of connecting coroplast sheets using acrylic connectors that I’ve developed.

Source Code

svn co https://lcalg.svn.sourceforge.net/svnroot/lcalg lcalg    
https://sourceforge.net/projects/lcalg/files/
  1. Check out the code. Download either of the two obj files and put them in the input folder.
  1. Adjust constants in util.constants.py to change most values in the program. Currently it’s set to use 2.5mm acrylic and ~3.5mm coroplast.
  1. Run LcAlg by running LcAlg.py. You’ll need python 2.7.
  1. Watch for updates. This is an early beta that I’ll be updating regularly.
Connectors

Coroplast is essentially plastic cardboard. It is lightweight and flexible, and bends rather than breaking. I now use it for the triangles, or faces, in my models.

I used to use acrylic plates for both the faces and the connectors. It was shatter-prone, heavy and expensive. I secured the faces to the connectors with first solvent glue and then cotter pins. This worked, but was labor intensive and in some cases fragile.

The solution is to use acrylic connectors and coroplast sheets. This leverages the strength of both materials. Because the coroplast is flexible, I use retaining tabs - the coroplast deforms around the rigid acrylic tabs and is locked into place

This forms a very strong connection. I have to pull very hard to force the pieces apart. However, I can easily remove a connector by slipping the retaining tabs over the coroplast retainer. Think zip ties - all it takes is a small piece of metal to jimmy one open but brute force will get you nowhere.



(By vector-cut I mean vector-etched)

Unfortunately, sharp angles lead to an issue that can be seen in this diagram: if angle A increases much more, distance B will decrease until there is not enough material there to hold the connector together

Large angle A’s can also lead to intersecting faces: In the diagram below, imagine if angle A were to increase. The two coroplast panels would quickly be intersecting. LcAlg solves this issue by calculating an offset and then removing that much material from the relevant edge.


Faces




A face is a flat coroplast triangle with 3 pairs of two mounting points for the acrylic connectors.

They’re cut out as below, to save laser time and material.

3 comments:

  1. I've had poor luck laser cutting coroplast. Enough power to cut through the "ribs" was too much for cutting through the surfaces, and left a sticky burned mess. The right power to cut through the surfaces would leave the ribs mostly intact.

    Maybe you're using a different sort of coroplast than I was? Can you maybe show a cross section of what it looks like, and discuss your laser power settings?

    Acrylic is my go-to material for laser-cut tomfoolery, but I agree that it's totally fragile, heavy and expensive -- being able to work with something like coroplast would be great.

    What's the most complex model you've made?

    ReplyDelete
  2. Here's the real beauty of it: I cut the coroplast at enough intensity to cut the surfaces and most but not all of each rib. That leaves a sheet of triangles that stays together but can be easily separated.

    And then, because coroplast doesn't take laser-etching that well, I take a pencil and draw in the labels on each face that tell me what connects to what. I used to etch these into the acrylic, but that took at least as long as just doing itself myself.


    The downside is that I have to do a little cleaning up with a razor where the ribs aren't fully cut.

    ReplyDelete
  3. I saw the Rhino head sitting in the Pit, and I was wondering, if the coroplast is commonly used as a printed sign material, are you planning on printing any textured models?

    ReplyDelete