February 2010 Archives

screen /dev/ttyS0 Hitting c seems to clear things, o goes to origin, and s begins scanning. No useful output yet, portmon on Windows proved essentially useless, but I have a full log of a picza scanning session in Windows as well.

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Using bazaar with the fab academy repository
This tutorial doesn't have the server setup part like the previous one did, and goes a bit more into managing files.

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I am still working on my Fab Academy 3D Molding and Casting project (a 3D model and cast of the TARDIS. The implementation of my model proved complicated.

The Fab Academy Assignment

• Machine a mold and cast parts in it

The Project: TARDIS multi-mold cast

Starting with the cad.py created .rml files (for details on the 3D modeling process see my TARDIS: 3D Modeling post), I carved several molds out a block of machinable wax using the Modela milling machine.

Wax Molds

There were a few mishaps creating these molds. The z-max setting was not high enough on the side mold (you can see where the Modela bit drug through the wax and made lines that were not part of the design.). I learned that it pays to set the z-max close to the max of 1 so that it will clear the edges of the design. However, because this particular design took so long to mill out , 7 hours or so, I opted not to redo it if the damage was minor. Instead, I attempted to repair the damaged areas with wax.

After I made the wax molds, I made casts of each side and the roof using urethane rubber. The door was cast once, but the side needed to be cast 3 times to create the 3D object.

I did not allow for space at the top of the wax molds, so to ensure that the rubber would have enough room to capture the top of the design, I laser-cut some tempered masonite frames in to increase the vertical space for the rubber to fill. These frames also make it a little easier to get the rubber out of the mold.

Creating and Gluing the Frames

Mixing Urethane / Creating the Molds

At Fab Academy Providence, we used a smooth-on 2 part urethane mold mix. Just mix equal parts of each container (A and B) and mix slowly in a figure eight pattern to minimize the bubbles.

What I learned about this material:

• Mix very thoroughly. Take your time (at least 10 - 15 minutes if you can stand it). The end result will be sticky if the parts are not mixed together well - My first two molds were sticky.)

• Add heat. Heat both accelerates the process and creates a less sticky end product. I used a desk lamp positioned in close proximity to the freshly poured mold.
• Be careful not to leave the heat on longer than 15 minutes or so and let the wax and rubber cool before removing the rubber mold from the wax.
• I learned the heat lesson the hard way when my mold melted from excessive heat. (see photos below)

Beware of Melting Molds

All The Molds (Good and Bad)

Skills Learned

Tools Used

Next Steps:

• Create a box and system for keying in the sides of the police box so it can be cast.
• Get LED, resistor and battery to wire up the light on the top.
• Cast in hydrastone

The Fab Academy Assignment

• Make a press-fit construction kit

The Project: Laser-Cut Playing Cards Construction Kit

When reading through instructables.com, I found a great pattern for a polygon construction kit. I thought I would use it for my first laser cutter / computer controlled cutting project at Fab Academy. The instructable I reviewed is for a plastic lamp shade, but I decided to use playing cards instead and make a construction kit minus the lamp. (Also, the cards are too opaque for a lamp and I didn’t want to take a chance with heat in such a small space.) In the end, I created a sculpture construction kit.

Laser Cutting the Cards:

Laser Cutting Video:

Putting Together The Construction Kit:

This construction kit shape can be put together to form a variety of shapes.

My Final Construction:

Skills Learned

• I leaned how to use Inkscape to create files that would create cut shapes when sent to the laser cutter.

Tools Used

• Epilogue Mini Laser Cutter
• Inkscape

Published in the MAKE Blog.

Our assignment this time around was to design a circuit board, mill it, and program it in Assembly language. Each student had to become acquainted with the following work flow:

• Designing the board
  
• Machining
  
• Stuffing components
  
• Programming
  

Makeda Stephenson in the Providence Fab Lab

In a Fab Lab, circuit boards are either milled from copper-clad PCB stock or cut on a vinyl cutter from copper tape with conductive adhesive. We try to avoid the etching process in order to limit the used chemistry we have to deal with. Whether etching or cutting, the first step is to choose one of the options for creating a tool path to send to the machine:

1. Draw the circuit as a black and white PNG image and bring it into cad.py for tracing.

2. Draw the circuit using Eagle, a free PCB drafting tool, and export Gerber files, a standard format for PCBs. Gerber files can be converted into PNGs using gerbv or the online tool from circuitpeople.com. Bring the PNGs into cad.py for tracing.

3. Draw the circuit in Eagle and use Eagle's CAM processor to generate mill and drill files that can be sent directly to the machine. This process was described by Marc Boon in a workshop at the Amsterdam Fab Lab in 2008.
   

I designed a boombox in Sketchup and I milled it out on the Modela in hard wax, using a 1/16" bit. I like how the tool path left a fine pattern on the surface. This model radio measures 3.5" across, and it began as a block recycled from scrap bits of wax, hence the air bubbles and the stray chunk of wood on the upper right edge.

My year project will be a diorama of a mechanical dance party on a base, and the ceiling above the dance floor will be a functioning record player. The moving figures and the record player will all work on the same motor. I'll be casting these boomboxes in different materials to position around the diorama.

This article was written for the MAKE Magazine blog.

Since October of 2009, a handful of small groups of students have been taking part in an educational experiment called the Fab Academy. The Fab Academy is a distance learning collaborative that's built on the infrastructure of the Fab Lab network. Labs in Spain, Iceland, Kenya, Amsterdam, India, and Rhode Island participate in Wednesday morning lectures by videoconference. The curriculum is concentrated into two week topics with a project due at the end of each and a more ambitious annual project due at the end of the year. This series of articles for the Make: Online will follow each of the two week sessions in the curriculum and highlight the work, tools, and techniques being developed in the pilot year of the Fab Academy.