Letters From the Fab Academy, Part 4

In this series, “Letters from the Fab Academy,” Shawn Wallace, member of AS220, the Providence, RI community arts space, shares his experiences with the Fab Academy, a distributed learning collaborative, built on the infrastructure of the Fab Lab network. — Gareth

3D Scanning

By Shawn Wallace

Victor Freundt prints a project using the ZCorp printer at the Barcelona Fab Lab.

When working with 3D scanning and printing equipment, it quickly becomes apparent that objects are nowhere near as fungible as MP3s. We’ll have to wait a while for the day when every teenager is capable of casually copying real-world objects. However, it is surprisingly easy to hack together a crude 3D scanner from commodity cameras, projectors, and hardware you probably have in a couple of junk drawers in your shop.

A good place to start is with the Modela mini mill, which has a piezo-based needle sensor attachment that can be used for scanning small objects. The machine records the plunge depth at the point it contacts the object and the software that comes with the Modela (Dr. Picza) converts these points into a 3D mesh. Here’s an example of using Dr. Picza to scan a small shell from Benito Juarez from the Barcelona Fab Academy site:

In my opinion, this is one of the more interesting applications of hobby-scale 3D scanning right now: sampling natural forms to riff off of, like this architectural model derived from the shell:

Unfortunately, Dr. Picza only works with Windows, so it’s not an ideal solution for a Fab Lab. Noah Bedford, of the Providence Fab Lab, made some progress reverse-engineering the scanning interface to the Modela MDX-20, but if anyone has leads on getting this to work under Linux, please contact us!

Barcelona ran a workshop that implemented a “milk scanner:”

The milk scanner is a setup where an opaque liquid is gradually added to a trough around an object and progressive photographs are taken as the object is submerged. The photos are then stitched together into a 3D model:

As part of the assignment, “extra credit” was awarded for printing the same object that you scanned:

In Providence, we began building the Fluxamascanner portable 3D scanner based on the Splinescan project, featured in MAKE Volume 21. Our scanner uses a dollar store laser pointer, a scrounged web cam, and some trigonometry to assemble a cloud of points on the surface of an object. The Fluxamascanner is a light-safe enclosure with an Arduino-controlled turntable designed by Elliot Clapp:

…but it still needs some work. It took us a little time to figure out a decent way to make a 3D mesh from a point cloud. We ended up using MeshLab, an open source tool particularly useful for editing and cleaning data from 3D scanners. A point cloud can be brought into MeshLab as a PLY file, a simple ASCII format for 3D object description. A canonical PLY file representing the 8 vertices of a cube looks like this:

ply
format ascii 1.0
element vertex 8
property float x
property float y
property float z
element face 0
property list uchar int vertex_index
end_header
0 0 0
0 0 1
0 1 1
0 1 0
1 0 0
1 0 1
1 1 1
1 1 0

To convert this simple “point cloud” version of a cube into a printable file, you bring it into MeshLab and apply the “Convex Hull” filter. This will connect the 8 vertices into 12 triangulated faces that can be saved as an STL file that should be printable. You’ll find that 3D scanned data sets will require much more hand editing to get to a mesh that is printable.

A simple point cloud before (left) and after the application of the Convex Hull filter (right)

In two weeks: Part 5: Sensors, actuators and displays!

More:

• Letters From the Fab Academy, Part 3
• Letters From the Fab Academy, Part 2
• Letters From the Fab Academy, Part 1

From MAKE magazine:

MAKE Volume 21 is the Desktop Manufacturing issue, with how-to articles on making three-dimensional parts using inexpensive computer-controlled manufacturing equipment. Both additive (RepRap, CandyFab) and subtractive (Lumenlab Micro CNC) systems are covered. Also in this issue: instructions for making a cigar box guitar, building your own CNC for under $800, running a mini electric bike with a cordless drill, making a magic photo cube, and tons more. If you’re a subscriber, you may have your issue in hand already, and can access the Digital Edition. Otherwise, you can pick up MAKE 21 in the Maker Shed or look for it on newsstands near you!