Inexpensive Ceramic Shell: Aluminum Casting with Drywall Joint Compound

We’ve been aluminum casting at the Milwaukee Makerspace since November, and I have cast several things since then.  For simplicity, we started by using a lost foam casting method, wherein the form to be cast is fabricated in Owens Corning Foamular 150 (Styrofoam), and is then tightly packed in a reusable, oil bonded sand called petrobond.  The molten aluminum is poured directly on the styrofoam, vaporizing it.  Because the mold is made of sand, the surface texture on the cast aluminum part has the “resolution” of the grain size of the sand.

Ceramic shell is another technique often used in art casting.  The positive of the form to be cast in metal is first created in wax, which is then dipped repeatedly in a silica slurry, that slowly builds up to the desired ½” thickness.  The surface detail reproducible is much smaller/better, as the silica has a much finer “grain size.”  The piece is then put in a kiln to burn out the wax and harden the silica, thereby forming an empty mold.  Typically the mold is cooled, inspected for leaks, patched, and then is buried in regular sand.  Note that to avoid fracturing the mold, it must be heated before pouring.  With all these steps, this process is relatively time consuming and is also somewhat expensive.

Recently, I read a blog post about a quick and low cost ceramic shell alternative that substitutes one or two coats of watered down “Hamiltons White Line Drywall Texture mix” for the tedious ceramic shell process outlined above.  While I couldn’t find that exact product, 4.5 gallon buckets of Sheetrock brand lightweight drywall joint compound (DJC) are omnipresent.  Note that some bags of quick setting drywall joint compound are actually just plaster, and cannot be substituted. I first assembled all the parts needed to make a quick test of the process.  I decided to make some aluminum packing peanuts:

Aluminum_Peanuts_parts

I hot glued the pyramid shaped sprues to the round cup and to the peanuts themselves:

Aluminum_Peanuts_together

I removed half of the 43 Lbs of DJC from the bucket, and poured in 10 lbs of water, taking care to mix it thoroughly with a spiral paint mixer connected to a drill.  Then, I just dipped the whole styrofoam assembly into the bucket, let it dry overnight, and dipped it in a second time.  Immediately after the first dip, I took care to brush the surface of any especially undercut areas, to prevent air bubbles from sticking to the surface.  In the future, I may consider pulling a vacuum on the bucket of DJC to de-gas it.  This may help prevent the formation of air bubbles on the surface of the styrofoam parts.  In addition, I could have first dipped the assembly in surfactant. After two dips, the 1/8” thick shell on the assembly looked like this:

Aluminum_Peanuts_coated

It was a week before the next aluminum pour at the Makerspace, during which time I poured a half ounce of acetone into the mold to dissolve the polystyrene packing peanuts and styrofoam, producing an empty mold.  This step is only necessary when casting packing peanuts, as their polystyrene tends to rapidly expand out of the mold and catch fire, while the pink styrofoam (also polystyrene) is made for homes, and so is much better behaved.  I buried the now-empty DJC mold in ordinary sand, and Matt W fired up the Bret’s furnace, melted a #16 crucible of aluminum, and poured it (Thanks guys!).  After fifteen minutes, I pulled the mold out of the sand, and found the DJC was a little darker.  The act of pulling the mold out of the sand an leaving it to cool over night left it somewhat cracked:

Aluminum_Peanuts_cast

The DJC crumbled off so easily that I didn’t even need a brush.  Also, I noticed that there is more yellowish surface tarnish on pieces left in the DJC to fully cool.  I recommend removing the DJC immediately after the aluminum solidifies.

Aluminum_Peanuts_cleaned

After making a few more, I’m almost ready to safely pack valuables, such as my “Marquis, by Waterford” crystal stemware:

Aluminum_Peanuts_in_use

Finally, check out the phenomenal surface detail that this process can reproduce.  For scale, this peanut is 1.5” long.  The surface texture on the front face is about ~0.002”!

Aluminum_Peanut_closeup

Thanks to Jason G for this last photo.  Also, a big thanks to Dave from buildyouridea.com for letting me know that one or two dips will do it!

We are Ready To Move This MMESSSSS!

There is quite a lot of packing happening at Ye Olde Milwaukee Makerspace (at Chase), in preparation for the move to our new home on Lenox!  In the midst of the chaos, the Milwaukee Makerspace Eight Speaker Super Surround Sound System, although taken down from the ceiling and put on a pallet, is still rocking!  The whole pallet really is a portable plug and play audio system: It has one power cord, and one headphone jack to plug your phone (or other audio source) in to.  With its eight speakers aimed in nearly every direction, it is sure to delight!

Hey, is that a MakerSpaceInvader pinball machine, a MAME cabinet, an RFID-enabled Kegorator, and a jewelry wax carving CNC machine next to the MMESSSSS?  What other odd things does the Makerspace have you ask?  Well, stop by and find out!

FEAR

 

I’ve updated Robert Indiana’s iconic sculpture “LOVE” for our times!  While “Love” may have been an appropriate sentiment from 1964 to 1970 when the 2D and 3D versions were made, I think that the revised text is more appropriate for the 2000′s and 2010′s. Fear is 8” tall and 4” deep, and while not a monumental outdoor sculpture, FEAR appears fairly sizable on a table top.

Fear, which is solid aluminum and weighs over 7 lbs, was cast last Thursday with quite a few other pieces.  The great thing about having an aluminum foundry at the Makerspace is that the whole thing cost about $7!  - $4 for propane, $1 for Styrofoam, and $3 for some Rotozip bits.  If FEAR were cast in bronze, it would weigh over 20 lbs, which would cost $200 for the metal alone.  As it is, we melted down old heat sinks, stock cutoffs and hard drive frames, so the metal is essentially free.

In the spirit of Indiana who made his own font, I drew FEAR up in Inkscape using Georgia Bold, but I increased the height of the Serifs a bit.  Shane helped me with the file manipulation and G-code generation (Thanks!), so I could use the CNC router to cut FEAR out of styrofoam.  I exported FEAR’s hairline thickness outline as .dxf so it I could bring it into CamBam to generate the G-code. The outer contour of FEAR was selected, and the following settings were chosen:

  • General -> Enabled -> True
  • General -> Name -> Outside
  • Cutting Depth -> Clearance Plane -> 0.125 (inches)
  • Cutting Depth -> Depth Increment -> 1.05 (inches)
  • Cutting Depth -> Target Depth -> -1.05 (inches)
  • Feedrates -> Cut Feedrate -> 300 (inches per second)
  • Options -> Roughing/Finishing -> Finishing
  • Tool -> Tool Diameter -> 0.125 (inches)
  • Tool -> Tool Profile -> End Mill

Identical settings were chosen for the inner contours of FEAR, with the exception of General -> Name -> Inside.   Then, I just selected “Generate G-code.”  Check out the real-time video of Makerspace CNC router running the G-code and cutting out the 1” thick Styrofoam (Owens Corning Foamular 150).

After cutting four 1” thick pieces, they were stacked and glued together.  I buried the foam FEAR in petrobond, and then attached Styrofoam sprues and vents.  For a more complete explanation of the quick lost-styrofoam casting process, check out this post.   Stay tuned for details of our next Aluminum pour, which will be in January in the New Milwaukee Makerspace!

 

SAGA: Semi-Automatic Gmail Assistant

My friend Rob is a smart engineer, and throughout the course of a work week he receives dozens of requests for his assistance on various projects.  He’s such a positive and helpful person that he finds it difficult to say “No.” to any of these requests.  I’ve helped him out by making a USB device that can provide a clear and simple email response to some of these requests.  SAGA, or Semi-Automatic Gmail Assistant, is approximately the size of a mouse, and plugs into a computer just like any mouse or keyboard would.  Here is the first prototype:

SAGA comes complete with a key lockout feature that prevents accidental activation. Once a worthy email request has been received, Rob can calmly make the call whether or not to arm SAGA by inserting the key, and rotating it clockwise 90 degrees.  After rotating the key, an octagon of LEDs lights up around the chrome button, enticing Rob to press it.  The extra illumination from the LEDs also further highlights the artfully coiled wiring that fills the prototype SAGA.  When the button is pressed, SAGA sends the keyboard shortcut to respond to the email and types out “Go F*** Yourself.” at a respectable and slightly humorous 200 wpm.  After waiting a half second for dramatic effect, SAGA automatically sends the email.  Note that there is a 1% chance that SAGA will instead respond “That’s a Great idea, I’ll get right on it!”

SAGAis powered by a Teensy 2.0 and $15 of electronics parts.  SAGA appears to the computer as a standard keyboard, and some helpful startup hints I followed appear on RasterWeb! and here.  One enabling trick was using a 2n2222 NPN transistor to drive 140 mA into the eight LEDs (connected in parallel), as this value exceeds the current available from any one of the Teensy’s outputs.  Note that keyboard shortcuts must be enabled in Gmail settings, and that Yahoo! Mail is also SAGA compatible. Upon moving an internal jumper, SAGA is probably compatible with some versions of Outlook (although installation of service pack 3.0 may be required).

Due to popular request by the few folks who have seen SAGA in action, I’ve built up a few, and they are for sale now on Etsy.  Check out the aesthetically pleasing, high gloss powder coated aluminum enclosure! Here is SAGA in high-speed yellow:

Alternate colors are available too – Just follow this link to Etsy!  

Makerspace Aluminum Casting Foundry

I arrived at the Makerspace on Thursday without an idea of what I would cast in metal, and in less than two hours I was removing my piece from the steaming petrobond! Check out the fruit of two hours of labor cast in metal!

That’s right! The Milwaukee Makerspace had its first (and second) aluminum pour on Thursday! Thanks to the hard work of several members, the Makerspace now has a fully functional aluminum casting foundry.  The custom built propane and diesel powered furnace melted an entire #16 crucible of aluminum in less than 20 minutes.  Check out Brant’s video to see our fearless foundry foreman leading the two pours!

To get the foundry running quickly, we’ve started out by using a lost-styrofoam casting method.  That is, styrofoam is carved into the desired shape and then a sprue and vents are attached with hot glue(!).  This assembly is placed in a wooden form, and is surrounded by tightly packed petrobond, an oil bonded, reusable sand.   Then, the molten aluminum is poured directly onto the styrofoam sprue.  The styrofoam is instantly vaporized by the 1250 degree Fahrenheit aluminum, which fills the void in the petrobond formerly occupied by the styrofoam. The air and perhaps even some of the styrofoam residue escapes from the mold through the vents.  We’ll be phasing in bonded sand and lost wax casting soon, so stay tuned for those details.

Eventually we’ll be having aluminum casting classes; however, we’re definitely going to be having aluminum pours on alternate Thursday evenings for the next few months.  Join our mailing list / google group to get more details.  Metal pours are spectacular to watch, so feel free to stop by to see the action around 7 or 8 pm, or join the Makerspace and participate!

More Banned Nerdy Derby Cars!

I made the car “Sling Shot” to enter in the recent 2012 Milwaukee “Nerdy Derby.”  During a few initial test runs, my car proved to be more than 10 times faster than the super-clever winning car made by HaveBlue.  Unfortunately, my  car was banned from competition because it was considered a threat to the spectators’ safety!  The consensus was that it had “too much momentum, or energy,” and would hurt someone if it went off the track and hit them.  What does too much energy mean, you ask?  Well, kinetic energy is ½ X Mass X Velocity^2.  Really then, the car was banned because the velocity is too high: It is just too fast!  I’ve already minimized the mass by making the car out of pine, although I could have made it from Balsa Wood, or even entertaining alternate materials such as these.

Anyway, its no fun to think of how to slow Sling Shot down so that its slow enough to safely race, but still fast enough to win.  Instead, I made some new car prototypes that amp up the speed and danger.  If I’m going to be banned in the future, I may as well get banned with style!

Below is a photo of Sling Shot, which traveled the 40′ track length is 0.1 or 0.2 seconds, for an approximate average speed of 300 feet per second, or 200 mph!  Note that the block is anchored to the finish line, thereby stretching the surgical tubing which acts as a spring to propel the car.

I realized that the dominant energy loss mechanism is air resistance – largely because Sling Shot’s wheels don’t even touch the track.  You see, the car doesn’t follow the contour of the track, it just heads directly to the finish line, through mid-air.  I spent some time engineering a more aerodynamic shape to further boost Sling Shot’s speed, searching for a shape that would really slice through the air.  I even consulted a team of highly trained German aeronautical engineer friends, who all approved of my slingshot propelled Henckel Car.  With the improved aerodynamic design, it should easily be faster than the 200mph Sling Shot car shown above.

The other car I built this weekend is also based on Sling Shot, but incorporates some classy chandelier bulbs.  The numerous ‘safety’ lights alert the time keeper of the imminent arrival of the derby car – for safety.

Lasers + Whisky = Delightful Wedding Gift

One of our members got married yesterday, and I crafted a fine gift for him and his wife at the Makerspace.  The happy couple enjoys whisky, and I thought that providing a tour might be a nice idea.  The tour starts at inexpensive bourbon, moves through wheated whiskies, and on to rye. The tour continues in Scotland with some easy to enjoy Sherry cask finish bottlings, and then moves on to rare, Islay and finally mature bottlings (25 Year old Talisker!).

I found some old mohogany baseboard that had some aging varnish on one side and some old caulking on another.  After cutting two 18″ long sections, a few minutes of belt-sanding had them looking great.  I used a 1 1/4″ Forstner drill bit to bore 0.3″ deep pockets for the bottles to fit in.  I used one of our two laser cutters to etch the name/age/proof of each of the whisky sample on top, plus a congratulatory message on the reverse side.  To bring out the rich orangy-red mahogany color, I wiped on Beeswax / Mineral Oil .  Check it out close up, while imagining the symbolism of things getting better with age!

Nerdy Derby Car From The Future

I made the car “Sling Shot” to enter in the 2012 Milwaukee “Nerdy Derby” at Barcamp7 this weekend.  A lot of people were talking about adding motors and fancy electronics, but my car is powered by a spring – a 10 foot length of surgical tubing that is stretched to another block of wood that must be clamped down.  I added wheels, but they aren’t necessary – they don’t actually even touch the track.

Check out what may end up being the only two runs the car has.  Fortunately, JRock captured some video of them.  I’d estimate that the car took 0.1 or 0.2 seconds to travel the 40 foot length of the race track, giving an average speed of 300 feet per second (200 mph!).  The great part about this “sling shot” design is that the car is accelerated by the surgical tubing spring throughout the first 30 feet of the track – until the surgical tubing is completely unstretched.  “Beautiful!”

 

Arduino-Powered Surround Sound Synthesizer

The Makerspace Eight Speaker Super Surround Sound System(MESSSSS) has been supplying music to the Makerspace for quite a while now, but I identified a problem even before the system was fully installed.  Stereo recordings played back on two speakers are great if you’re in the “sweet spot.” If not, traditional approaches to 5.1 audio improve things, but all rely on there being a single “front of the room.” Unfortunately, it’s not clear which side of the 3000 square foot Makerspace shop is the front, and with four pairs of speakers in the room, even stereo imaging is difficult.

Fortunately, I’ve just completed the Makerspace Eight Speaker Super Surround Sound System’s Enveloping Surround Sound Synthesizer (MESSSSSESSS).  The MESSSSSESSS takes stereo recordings and distributes sound to the eight speakers in an entirely fair and user configurable way, thereby eliminating the need for a “front of the room.” Now listeners can be arbitrary distributed throughout a room, and can even be oriented in random directions, while still receiving an enveloping surround sound experience!

The MESSSSSESSS user interface is somewhat simpler than most surround sound processers, as it consists of only four switches and one knob.  Somewhat inspired by StrobeTV, the simplest mode references questionable quadraphonic recordings, in that the music travels sequentially from speaker to speaker, chasing around the room either clockwise or counterclockwise at a rate selected by the knob. With the flip of a switch, sound emanates from the eight speakers in a random order. Things get considerably less deterministic after flipping the Chaos Switch, adjusting the Chaos Knob, and entering Turbo Mode:  Its best to visit Milwaukee Makerspace to experience the madness for yourself.  I’m legally obligated to recommend first time listeners be seated for the experience.

The MESSSSSESSS is powered entirely by an Arduino Uno’s ATmega328 that was programmed with an Arduino and then plugged into a socket in a small, custom board that I designed and etched at the Makerspace.  The ATmega328 outputs can energize relays that either do or don’t pass the audio signal to the four stereo output jacks.  Care was taken to use diodes to clamp any voltage spikes that may be created as the relays switch, thus preventing damage to the ATmega328 outputs.

As shown by the minimal part count above, using the ATmega328 “off the Arduino” is quite easy:  Just connect pins 1 (The square one), 7 and 20 to 5 volts, and connect pins 8 and 22 to ground.  Then, add a 22uF cap and small bypass cap between power and ground, and a ceramic resonator to pins 19 and 20.  You can even use an old cellphone charger as the power supply.  Boom.  That’s it.  The real benefits of making your own boards are having a well integrated system, and cost, as the Atmel chip is $4.50 while a whole Arduino is $30.  Also visible in the photo are a programming header and the two ribbon cables that route all the signals to and from the board.