This was a really cool project and seems to be successful. I’m hoping to continue and try some more interesting forms beyond text. I think cutting-edge fabrication technology is at it’s best when combined with established/non-digital techniques–it’s the best of both worlds!

This pour took place at the Butler Street Foundry in Chicago.

Laser-cut Form for Bronze Casting

The Final Product: A Cast Bronze Plaque

A Deep Raster Engraving With a Tapered Shoulder Makes for a Great Plaque Form

A Two-part Sand Mold Will Recieve the Molten Bronze

Casting Sand Packed into the Mold Holds an Impression of the Laser-cut Form

Casting Sand is a Mixture of Sand & Clay; Imagine the Best Sand-Castle Sand, Times Ten

A Gas Furnace is Used to Melt the Bronze

Solid Bronze Goes into the Furnace to Melt

Solid Bronze Goes into the Furnace to Melt

Lifting the Lid off the Furnace

The Molten Bronze is Lifted Out of the Furnace in a Container Called a Crucible

Molten Bronze Hoisted out of the Furnace

Molten Bronze Hoisted out of the Furnace

Molten Bronze in the Crucible

Molten Bronze Poured from the Crucible into the Two-Part Sand Mold

Molten Bronze Cools in the Two-Part Sand Mold: Weights are Placed on Top to Contain the Hydraulic Pressure Created in the Mold

After About 20 Minutes, the Bronze has Cooled Enough to be Released from the Two-Part Sand Mold

Bronze Casting Released from the Two-Part Sand Mold

The Final Product: A Cast Bronze Plaque

Laser cutting is a great technique for quick fabrication, in part because of the very small point size of the laser beam. The minuscule kerf of a laser cut allows for very tight 90° angles on interior (and exterior cuts).  This makes it easy to laser-cut thin panels of material for joining, as oomout demonstrates in this post on instructables.com (example pictured below). One of the drawbacks of laser cutting is the limited depth of materials that can be successfully through-cut; the laser cutter that I have access to can get through about 1/2″ of MDF or plywood, but the cuts are very charred and not perpendicular due to the hourglass shape of the laser’s focal point.

T-Bolt connection using laser-cut 1/4" panels

CNC routing is another great technique for quick fabrication. The range of material depth is much greater, there’s no burning, and through-cuts are perpendicular. One of the biggest drawbacks, however, is the inability to route interior corners due to the cylindrical shape of the cutting tool. This can require tedious hand-finishing to file or chisel out the interior corners to 90° angles, which is not worthwhile for projects that don’t have to look pretty, i.e. prototypes.

The technique pictured above is achieved by simply routing an extra bit of material out of interior corners to allow for 90° butt-joints. To set the paths for the corner knock-outs, a circle is created at each interior corner using a 3-point definition; the first point is set on the corner’s intersection, the second two are placed on each edge of the corner at a distance equal to the diameter of the router bit you plan on using. This will make sure enough material is taken away to allow for a 90° joint.

Vector path for 1/4″ laser-cut t-bolt joint (.dxf)

Vector path for 1/2″ CNC-routed t-bolt joint (.dxf)

It’s true! You can have multiple webcam feeds in your swf/as3 application. Here’s how:

1. Plug in your webcams.
2. Look in your Flash Player’s Camera Settings Panel. You might have to open an existing swf to get here. You should see a dropdown list of all the cameras available to you. The first camera on the list is camera 0, the second is camera 1, and so on. Remember the numbers of the cameras you want to work with (In my case, I want #7 and #8).
   
3. Call your cameras with Actionscript 3. Here’s the code, and here’s a FLEX project.
4. A few pointers: be careful about plugging/unplugging the cameras. Flash Player seems not to like this, you may have to quit and restart to refresh the list. You can adjust how and where both video feeds are placed in the scene. In this example they’re layered on top of each other with the blend mode set to OVERLAY, which [sort of] averages the two feeds together.
5. Only see one camera? Depending on your camera & drivers, your computer may not recognize two identical cameras at the same time. Cameras with different hardware should be recognized, though.

Also, I am using Playstation 3 Eye cameras, because they are great in low light and have high frame rates, and are pretty cheap. You can get drivers for Windows and Mac since they are not recognized automatically. Have fun!

Above is an example of varying speed settings with vector cuts and engravings on a 120W Co2 laser cutter. The ratios of power to speed are roughly the same on both groups of cuts, producing approximately the same depth; however one speed setting is much higher (30x) than the other, producing the wobbly lines on the fast group. The faster setting was enough to cause the laser’s Y axis to lose registration, as you can see on the two bottom lines of text.

Keeping a low speed is not necessary for all cuts, just those with small or intricate paths which cause the head to change position rapidly. Straight cuts with a higher speed usually look just fine.

Colors in the screenshots are only intended to distinguish between steps. Enjoy!

The final product should look something like this Webcam file with all steps (.3dm, 16mb)
Step 1.a Start a new file (small obj/inches)
Step 1.b In the Top viewport, draw 2 concentric circles, centered on 0, 1″ and 2″ diameters respectively.
Step 2 Copy and paste the smaller circle in place.
Step 3 Turn on Osnap and activate Cen only. Activate Move command, snap to Cen of copied small circle, then type <45 to add an angle constraint.
Step 4 Move small circle outward so that it intersects with the outer circle.
Step 5 Activate the ArrayPolar command. Select the small circle to array. Set 0 as the center of the array. Set the number of items to 4. Set the angle to 360. Hit Enter.
Step 6.a Select the four small circles. Activate the Split command, and split the large circle.
Step 6.b Select the large circle, then activate the Split command and split the four smaller circles.
Step 7 Select the four larger segments of the outer circle, and the four smaller segments of the outer circles–they’ll form a rounded cross-shape. Join these curves with the Join command.
Step 8 Turn on grid snapping. Select the innermost circle, and move it up one inch in the RIght or Front viewport by clicking and dragging.
Step 9 In the Front viewport, turn on grid Snap. Activate the Interpolate Points curve tool. To draw the first point, snap to the grid intersection on the x axis that is two inches to the right of zero. Then turn Snap off. Draw a line that is the approximate shape shown – it does not have to match perfectly. To draw the last point, turn Snap back on, and snap to the grid intersection that is 1″ above the x-axis and 1″ to the right of the z-axis.
Step 10 Select the curve you just drew, then activate the Offset command. Set the Distance to 0.04″, and offset below the original curve.

Taylor and I have been working on a DIY 3-axis CNC mill over the last few months. I’m posting this mostly to brag :), but also as an excuse to do some documenting on the process that might be useful to others. We’ll keep posting as things progress.

Some video of testing

The original plans use 1/2″ MDF for all the panels. We decided to go with with clear acrylic for the visual effect. Also, we were able to use a laser cutter for most of the cutting to the edges are nice and clean.  The downside is the brittle nature of acrylic, which likes to crack when drilled from the edge (and this design requires a lot of that).

CONTROLLER & CONFIGURATION

We’re using linux-based Enhanced Machine Controller to run the mill, with a modified version of the standard stepper configuration. Here’s our EMC configuration files. So far, I’ve been really pleased with the performance. It was trial-and-error figuring out the scaling– I ended up attaching a pencil to a dremel collet, then manually jogging each axis until I could draw a one-inch line in each direction. The scaling factors I came up with are: 520 for X and Y, and 16000 for Z, and that’s with quarter stepping set on the hardware controller board.

We kept getting a “Joint 2 Following error,” indicating that the z-axis was losing its position. I found that this was happening only when using  G00 (rapid-positioning) codes. I’m still a little unclear as to whether we need to even worry about positioning in this case, but for now I’m just replacing G00 codes in my toolpaths with G01 (linear motion). It’s a little slower, but for now the error is not happening anymore. See Feed Speeds for the permanent fix.

TOOLPATHS

We use Rhino3D and RhinoCam to generate our toolpaths. I’ve found that a number of different post-processors to work just fine, but mostly we’re using .NCD’s out of habit.

FEED SPEEDS

There doesn’t seem to be a way to directly set the feed and plunge speeds in EMC. The NCD post-processor defaults the feed speed to 3.7 and the plunge speed to 7.3 and the units are inches per minute. So we’ve been doing a search and replace in the post-processed files setting plunge to 14 and feed to 10 (this is easier than going back to RhinoCam to re-generate the toolpath with new feed speeds). We also then modified the MAX_FEED_OVERRIDE setting in the stepper_inch.ini file to 3, meaning we can increase the feed override up to 300%. We now limit the max override to 150%, and more deliberately set feed and plunge speeds in RhinoCam, under the Feeds & Speeds tab — these vary depending on material.

ERRORS

We kept getting a “Joint 2 following error” while testing, and found–after consulting the EMC documentation wiki–that changing the FERROR setting to 5.0 and the MIN_FERROR to 1.0 (that’s percent) for all axes in stepper_inch.ini alleviated this error. There’s the potential with increasing the FERROR settings of losing some accuracy, but that’s not our main concern at this point.

The situation: Steve* a former roommate of mine moved out, and left a box of things in our basement storage unit, including an old Apple iBook laptop. Even though our other three neighbors had access to the storage room, I wasn’t too worried about any of his stuff; the laptop was old, the battery & ‘Y’ key were broken, etc. Plus I know all of my neighbors, they are all women in their mid-to-late 30’s and I had no reason to suspect any of them of doing anything… let’s just say ’strange’.

At one point Steve sent a friend to pick up some stuff, and I assumed he had taken the laptop, because I noticed later that it wasn’t there any more.

I didn’t think anything more about it, since I never heard anything more from Steve. Until about a month ago, when I noticed that Steve’s laptop was connecting to our wireless network. I contacted him and confirmed that he did not have the laptop, nor did his friend. This pretty quickly led me to one conclusion: one of our neighbors had taken the laptop from our storage room, and was using it. On our network.

I found this situation to be pretty mind-blowing: that one of our adult neighbors would be so ignorant and unscrupulous as to take something and use it so flagrantly. It wasn’t so much the value of the computer that bothered me. The laptop, let’s face it, was a piece of shit. Beat up, old, and not containing any sensitive data, I would have had no problem loaning it out until Steve wanted it back. The principle of the situation was what really got under my skin: you don’t steal stuff from your neighbors, and if you do you certainly don’t advertise it to them!

Whoever had the laptop was basically waving a huge red flag saying, “I’m ignorant. Please take advantage of me.” At least that’s what first flashed through my mind--­­visions of vengeful data-mining, FBI raids, etc. But after the initial shock wore off, I realized what a delicate situation this was. I certainly could not go about blindly accusing each of my neighbors in turn–this would only offend the two who were innocent, and produce a denial from the guilty one. I did consider calling the police, or using a packet-sniffer to maybe track down the email address of the culprit. But even that seemed a little harsh; pressing charges or going to elaborate lengths to embarrass the guilty neighbor would also probably lead to an awkward living situation.

I decided that my ideal approach was to let the thief know that I knew about the theft, and that they could return it to the storage room with no questions asked. And I would let them know in a firm yet polite fashion. By remotely breaking the shit out of that laptop.

Luckily I was able to get the login information from Steve, giving me pretty much unfettered access to his machine over our network. This was my plan: to put the machine into kiosk mode, disabling all other applications and interfaces save for one–a never-ending popup loop with a [polite] message commanding the return of the laptop.

To do this I needed to do a few things:

• Disable the Dock
• Disable the Menu Bar
• Replace the Finder with the popup-loop app

I decided to start with the Finder-replacement App. I used Apple’s Script Editor to cobble the code snippet into an application bundle.

The bundle part is important, since it bundles an info.plist file with the script, which allows us to take control of the Dock and Menu Bar (We’ll get to that later).

Now to tell OS X to auto-start Stealer.app in place of Finder (which itself is an application), I placed Stealer.app in Steve’s Applications folder, then modified his com.apple.loginwindow.plist file (usually located in the Library/Preferences folder of the user’s Home directory) by adding the following lines:

<key>Finder</key>
<string>/Applications/Stealer.app</string>

This code causes Stealer.app to automatically launch in place of Finder. This makes it basically impossible to quit Stealer.app or navigate to and start any other applications.

Next was to hijack the Dock and Menu bar. This makes it very hard to launch any other applications besides Stealer. I did this by editing Stealer’s info.plist file (control-click on Stealer.app, selecting Show Package Contents), adding the following lines, and keeping the tags in alphabetical order:

<key>LSUIPresentationMode</key>
<integer>4</integer>

Since all these changes were taking place as the computer was running, and pretty well depended on it being restarted to work fully, I also took the precaution of moving all the Applications to a separate folder, then duplicating Stealer.app in the Applications folder, and renaming it iChat.app, iTunes.app, etc. This way the message would still appear without a restart. (I figured the surprise of realizing someone was remotely messing with your stolen computer would be enough to scare the thief into returning it.)

Two nights later, the laptop was back in the storage room, safe and sound. And later the same night, our upstairs neighbor coincidentally dropped by with a gift basket full of snacks, which she ‘just happened to have laying around, and thought we might like.’ She just moved out today. :)

Disclaimer: The solutions I came up with to deal with my situation are extremely specific and jury-rigged, and nowhere near foolproof. They are by no means the best solutions, they just happened to work in my situation. I wrote this post mostly because the situation was very weird, to the point of being comical, and it presented some opportunities to do some fun pseudo-hacking and learn a few things.