Weekend Project: Planter Boxes!

Last weekend I made three huge, turquoise planter boxes for my rooftop deck – check out the quarter for scale.  Naturally, help from other Makerspace members was key, as I relied on JackD and his JAMbulence for help transporting two sheets of plywood (Thanks!).  I safely sliced ’em up on the panel saw, and then glued, screwed and nailed them together.  After applying numerous coats of outdoor latex paint and a bit of sanding, they’re already in use in downtown Milwaukee!


Weekend Project: Kitchen Shelf

I’ve recently heard that the Milwaukee Makerspace has a reputation for only having members who are electronics enthusiasts. Well, in addition to the metal, wood, beerwater, whisky, fire, arduino, weldingoddaudiocasting, and numerous acoustic projects that I’ve worked on at the Makerspace, I’ve finished a few electronics projects here. My latest Makerspace weekend project is a shelf for my kitchen, pictured here with the Sad Bananaand three legged pig®.

Kitchen Shelf

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:


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


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:


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:


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.


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


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”!


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!



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!


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!

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!

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.

Audiophile Headphones

Sick of thin bass when listening to your favorite music over headphones? Missing that cinematic surround sound experience when you are on the go? Craving the visceral bass impact of live concerts? Trying to get to 11, but your headphones are stalled out at 6.283?  Move over anemic earbuds, there’s a new product in town: BIGheadphones: Bass Impact Gear’s new headphone product, available in two versions: Premium 5.1 (shown below in a user trial) and Mega Premium 7.2 (coming soon).

Reviewers are raging about the unprecedented dynamics, midrange clarity, and sound stage:

“Perhaps it was in the region of articulation and musical dynamics that this system impressed the most.  The dynamic bloom from soft to extremely loud was exquisite, and so clearly delineated that listeners could unravel musical phrases down into the concert hall’s noise floor and below.” The Audio Critic

“BIGheadphones speak with an organic integrity. They are hewn from the living woodendangered old growth Amazonian timber… I wept openly when forced to return the demo model.”– Stereophile

“BIGheadphones make critical listening a joy rather than a strain.  I was flabbergasted by their brilliant pitch certainty.  The midrange sounds were open, clear, and stunningly present. Playback performance like this makes use of the word transparent not only forgivable, but mandatory.” Audiophilia

“The 5.1 has an innate flair for speed and control that is incomparable. The command of bass dynamics moves beyond effortlessness to nonchalance. My eyeballs were vibrating! My hands are still shaking as I write this review.”Sound and Vision

“…the most important innovation in audio reproduction since the permanent magnet.”  –Acta Acustica

“W.O.W.”Bose listening panel

Reviewers agree that BIGheadphones are a huge leap in audio reproduction technology, larger than vacuum tubes, Stroh violins, carbon microphones and Edison cylinders combined.

Relative to planar speakers, typical box speakers are unable to develop the proper surface loudness or intensity typical of large instruments such as the piano.  This audio feat poses no challenge for BIGheadphones. Computationally modeled and optimized by a small and highly trained team of expert acoustical engineers over a period of 13 years, BIGheadphones were inspired by ingeniously thinking “inside the box,” not outside the box.  At the obsolete exterior listening position, a typical loudspeaker rarely generates even a realistic classical music concert level, but inside that same speaker, the sound pressure levels can quite easily exceed the 115 dB of a stadium rock concert. This realization was the BIG breakthrough, but was only the beginning of the struggle pursued by our elite acoustical research team.  Our uberengineers had to break the chains of common design practice to breathe the refreshing mountain air of inside-the-box acoustics, where nearly everything is inverted.

To illustrate, achieving loud bass external to a speaker typically requires the box be a very large size.  However, inside the box, the bass response is naturally flat to the lowest frequencies, and the smaller the box the louder and more impactful it becomes. Further, our astute engineers shrewdly realized that the stop-band and pass-band inside and outside the box are also opposite, as illustrated in the enlightening plot below of the subwoofer section of BIGheadphones. The Blue curve shows the hyposonic level inside, extending well below 10 infrasonic Hz, while the Red curve shows the meager sound pressure level in the more traditional listening position two meters in front of them.  Notice how the passband outside the box begins at 2kHz, whereas the passband inside the box ends at 2 kHz.  How many other speaker systems can boast of a subwoofer response that is flat over more than three orders of magnitude?  Now that’s innovation!  And this is just the customer-average response—the bigger your head the broader the bandwidth that you can brag about to your audiophile friends.

The observant reader has already noticed that this plot shows BIGheadphone’s output level is a mere 142 dB – only 22 dB above the threshold of pain.  Note though that this is with a paltry 1 Watt input – in reality, they are capable of 17 dB higher output with the optional high output amplifier add-on kit, though this reduces the playback time to under 36 hours per charge.  And that’s just the subwoofer!  The industry-leading, consciousness-altering bass response shown above is augmented by five horn loaded, carbon fiber reinforced porcelain dome, 2” diameter neodymium tweeters with single crystal silver edge wound voice coils.  With this critical addition, the frequency response of the BIGheadphones extends from below 10 Hz to 31 kHz and beyond!  Get your BIGheadphone audition today at your local Hi-Fi retailer!  “BIGheadphones, the last audible note in audio reproduction!”

(Not available in France.)

Thanks to the editors at RSW, Inc.

Giant, Ominous Wind Chimes

A while back I bought five 4.5 foot long aluminum tubes because the price was so low that I couldn’t resist.  They are 3.25 inches in (outer) diameter, and have a wall thickness of 0.1 inches.  Recently, I decided to make them into the longest and loudest wind chimes I’ve ever heard.  The longest tube rings for over a minute after being struck by the clapper.  After thinking for a while about which notes I should tune the tubes to, I found that fairly large chimes are commercially available, but they are tuned to happy, consonant intervals.  I consulted a few musically savvy friends (Thanks Brian and Andrew!) to gather some more ideas for interesting intervals on my chosen theme of “Evil & Ominous.” I ended up with quite a few ideas, and with Andrew’s help, I sampled the sound of the longest tube being struck, and recorded mp3’s of each set of notes to simulate the sound of the chimes ringing in the wind.  I ended up with something delightful: D4, G#4, A4, C#5 and D5 (which are 294 Hz,  415 Hz, 440 Hz, 554 Hz, and 587 Hz).  That’s right, there are two consonant intervals (octave and major 5th), but look at all those minor seconds and tritones: Delightfully Ominous!

Then the science started:  How to determine the tube lengths to achieve the desired notes?  How to suspend the chimes so they sound the best, and are the loudest?  Where should the clapper strike the chimes in order to produce the loudest sound or the best timbre?

Wind chimes radiate sound because they vibrate transversely like a guitar string, not because they support an internal acoustic standing wave like an organ pipe.  Pages 152 & 162 of Philip Morse’s book “Vibration and Sound” show that the natural frequencies, v, of hanging tubes are given by the following expression:

Pretty simple, right?  One only needs to know rho and Q, the density and Young’s modulus of aluminum, l, the length of the tube, a & b, the inner and outer radius of the tube, and the beta of each tube mode of  interest.  Don’t worry though, there is a simpler way.  If all of the tubes have identical diameter and are made of the same material (6061-T6 Aluminum!), the equation indicates that the natural frequency of a hanging tube scales very simply as the inverse of the tube length squared.

Using the above relationship (frequency ~ 1/(length*length)) to compute the ratios of tube lengths based on the ratio of frequencies produces:

Length of D4 tube = 1.000 * Length of D4 tube

Length of G#4 tube = 0.841 * Length of D4 tube

Length of A4 tube = 0.817 * Length of D4 tube

Length of C#5 tube = 0.728 * Length of D4 tube

Length of D5 tube = 0.707 * Length of D4 tube

The longest tube is 133.1 cm (52.40 inches) long, so all the tubes were scaled relative to it.  Note that the frequencies are slightly different than the notes I was aiming for, but absolute pitch is only a requirement when playing with other instruments.

~D4 = 293.66 Hz = 133.1 cm = 280.3 Hz

~G#4 = 415.3 Hz = 111.9 cm = 396.4 Hz

~A4 = 440.0 Hz = 108.7 cm = 420.0 Hz

~C#5 = 554.37 Hz = 96.9 cm = 529.1 Hz

~D5 = 587.33 Hz = 94.1 cm = 560.6 Hz

How accurately do these tubes need to be cut?  For example, how important is it to cut the tube length to within 1 mm?  This can be calculated simply, using the above equation.  A length of 108.7cm gives 420.0 Hz, whereas a length of 108.8cm gives 419.23 Hz.  This spread is 0.67 Hz, which is a fairly small number, but these small intervals are often expressed in cents, or hundredths of a half-step.  This 1 mm length error gives a frequency shift of 31cents.  Does this matter?  Well, the difference in pitch of a major third in just and standard tuning is 14 cents, which is definitely noticeable.  It is preferable to be somewhat closer than this 1mm, or 2/3 Hz to the target interval.

The tubes were rough-cut to 2 mm longer than the desired length on a bandsaw to allow the ends to be squared up in case the cut was slightly crooked.  The resonance frequency was then measured by playing the desired frequency from a speaker driven by a sine wave generator with a digital display.  I then struck the tube and listened for (and counted) the beats.  If two beats per second are heard, the frequency of the tube is 2 Hz different than the frequency played through the speaker.  With this method using minimal equipment, I quickly experimentally measured the resonance frequency to less than 0.5 Hz (one beat every two seconds), which is ~10 cents.  I then fine tuned the tube length using a belt sander, and measured the resonance frequency several times while achieving the correct length.  In reality though, if I missed my target lengths I’d only be adding a little more beating and dissonance, which might have only added to the overall ominous timbre.

How to suspend the tubes?  Looking at the mode shapes of the tube for guidance, I suspended the tubes by drilling a hole through the tube at one of its vibrational nodes, and running a plated steel cable through it.  Check out the plot below from Blevins’ New York Times Bestselling book “Formulas for Natural Frequency and Mode Shape.”

This plot shows a snapshot of the tube’s deflection as a function of position along the tube.  Imagine that the left side of the tube is at 0, and the right side of the tube is at L.  This plot shows the first three mode shapes of a “straight slender free-free beam,” which my 1.33 meter long, 83mm diameter tube qualifies as.  Just like a guitar string, this tube has multiple overtones (higher modes, or harmonics) that can be excited to varying degree depending where the clapper strikes the tube.  The guitar analog of this is the timbre difference one hears when picking (striking) the string closer to or further from the end of the string (the bridge).  This plot also shows where the tube should be suspended – from the locations where the tube has no motion in its first, fundamental mode.  Those two places, a distance of 0.221L from the tube’s ends, are circled in red.  When striking the tube suspended from either of these locations, the tube rings the loudest and for the longest time duration (as compared with any other suspension location).  Similarly, when striking the tube in the location noted by the red arrow (the midpoint of the tube), the tube rings the loudest.  I won’t get into more math and fancy terms like “modal participation factor,” but it is true that suspending the tube from the circled red locations also results in the lack of excitation of the third mode (which has a motional maximum at this location).  Similarly, striking the tube at its midpoint results in the lack of excitation of the second mode, due to its motional minimum at this location.

Thanks to David for the Ominous Photo.   An Ominous Chime video will soon follow.