All posts by nouyang

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molding and casting research

I conclude that yes, hydrostone and drystone (which mas.863 has lots leftover) can be used for metal casting.

http://www.lagunaclay.com/catalog/pdf/lcc_plaster.pdf
USG PLASTERS & GYPSUM CEMENTS FOR ART, STATUARY & CASTING APPLICATIONS
DRYSTONE Fast-casting gypsum cement that provides strong, durable casts without the need for dryers. Excellent compressive strength and good
impact resistance. Enhanced flexural properties. Low absorption for reduced paint demand. Environmentally preferred to resin-based
alternatives. Available in solid or hollow cast formulas.

HYDRO-STONE Especially suitable where high strength and resistance to wear are necessary. Used in high-quality art and novelty castings, molds, figurines,
modeling material, anchoring material, density fill applications, lamp bases, and die production. Works well in most mold materials, especially
flexible molds. Expansion about two times greater than Hydrocal A-11. Self-leveling when poured and not suitable for hollow cast
applications

http://www.sheffield-pottery.com/US-Gypsum-Plaster-Information-s/38.htm  
DRYSTONE – Fast setting high strength product that needs no drying. An environmentally sound alternative to resin-based products. No hazardous chemicals or waste, no styrene emissions and no required environmental controls.
HYDRO-STONE – One of the hardest and strongest of all gypsum cements. When mixed properly, has a heavy, syrupy consistency ideal for pouring solid models or patterns. Recommended for stretch-press dies where extreme surface hardness is required. Slightly higher setting and expansion than ULTRACAL 30. Used for high quality art novelty and statuary castings.

http://en.wikipedia.org/wiki/Plaster_mold_casting
http://chestofbooks.com/reference/Henley-s-20th-Century-Formulas-Recipes-Processes-Vol1/Casting-Plaster-Molds.html 
plaster is used for metal casting but requires drying for several days

 http://www.artlex.com/ArtLex/G.html
gesso – Plaster or a fine plaster-like material made of gypsum, which is also called whiting, used for sculptures. An especially versatile medium in reliefs, gesso can be either a material cast in a mold or a material of a mold, a material to be modeled, or carved, or attached to something else. When used for molds into which molten metal is poured, it must be hardened with sand as a grog. Gesso may also refer to such a gypsum material mixed with an animal-hide glue and used as a ground for painting. For this latter use, it isWEAR A DUST MASK! usually applied to the surface of a wood panel or sculpture to become the surface on which an artist paints. It was used by Gothic and Renaissance panel painters, and is still used today. Oxgall (or another wetting agent) can be employed MEDICAL ALERT!to eliminate pin-holes in gesso surfaces by mixing it into the gesso before the gesso is applied. Like all other dusts, airborne gesso is hazardous to breathe — every user should wear an appropriate dust mask. Also see slip and stucco. 

therefore gesso is probably food safe.  so if I coat my pink foam model (which can cause sensitivity with prolonged exposure — cue architecture student horror stories) with gesso and then cast it with food-safe silicon, should be good.

overview of molding techniques
http://miniatures.about.com/od/techniques/tp/moldputtylist.htm

discussion of 3d-printing plaster molds
http://forums.reprap.org/read.php?171,37834,3783

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Nyancat party! in aluminum, egg, foam, silicone, hydrostone, and drystone

MAS.863, Fall 2011
Week 6
Molding and Casting — Nyancat party! in Egg, Silicone, Plastic, Hydrostone, Aluminum, and Foam

We can use molding and casting to easily replicate a design.
The analogies between this manufacturing process and internet memes are clear.
Thus, I am compelled to make nyancats!

nyanweight? nyancoaster?

Aluminum paperweight. File done in solidworks, export as DWG to Mastercam, turned on CNC lathe (daewoo puma) and milled with engraving tool to 0.02’’ depth on CNC mill (EZ trak). Used as mold positive.


Smooth-on OOMOO25 used as silicone mold (negative). 100 parts A : 130 parts B by weight, pot time ~15 minutes, cure time ~1 hour.
 
Masking tape used to form “walls” for negative mold.

Released fine (no releasing agent used). Fine features (0.02’’) reproduced cleanly.


Hydrostone casting, positive.

Final result: one nyancat party.

nyanegg?
Just for fun: some egg?
 
End result:
 

Not so great. I await the shopbot 3D mold.

hot glue mold: jello legos
Previously on Bad Ideas:
 

Hot glue is nontoxic, right? Legos used to create positive for hot glue. Crisco applied as releasing agent — did not release well, had to pry out legos, destroying them. Jello poured in — very nice, can even see the “LEGO” lettering on the bumps. Jello lego’s had flat bottoms though, since this is a one-part mold.

nyancake?
On Saturday, I learned that I now have media lab shop access and can now devote my entire weekend to MAS.863! Yay!

I made the model in Solidworks while still hoping I could get my hands on some food safe silicone. This didnt happen, though Iḿ not sure why. Ah well. I went ahead anyway and cut my model on the shopbot out of foam
.
1/8´’ bit, though later I remember I had resized my model specifically for a 1/4´’bit which could have cut my time down by half. After 1.5 hours of cutting I had my mold (the partworks estimate was 45 minutes). The deepest parts the shopbot just barely cleared (that was nervewracking!). The cut-out toolpath the shopbot most definitely did not clear — I was prepared and hit the e-stop button immediately.


There were a lot of burrs and the finish quality was less than what Id expected. But Iḿ not complaining, since Iḿ using a shopbot to cut out an internet meme…

I attempted to deburr with a heat gun but stopped immediately when I realized I was rounding out my beloved sprinkles. I ended up using an air compressor and getting pink sprinkles all over myself.
Then I cast a negative mold with smooth-on silicone, in this case mold star slow since the arch shop was out of oomax 25. Pot time 50 mins, cure time 4 hours. After 1.5 hrs I took my mold with me instead of waiting. Mold turned out fine. Probably used half a smooth-on set of material.


I had to commit some violence to the mold original in order to get the silicone out, simply due to the geometry of the piece. The silicone separated from the foam just fine.

Drystone casting followed. Required almost exactly ~1.5 cups of material. (500grams?)

Oh, this reminds me, I´ve done sand casting before too. We helped sand-cast a cement health-friendly stove in La Vaquita, Mexico. This was a government initiative of some sort.

Files coming soon. [edit: 4 Sept 2012. So maybe not soon. But I’ll try to get around to it. Also I would like to point out to blog readers that I went on to make nyancake and nyanjello! 😀 http://www.orangenarwhals.com/search/label/nyancake

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centrifugal switches (spin activated yoyo electronics)

doing some research for 2.008 instead of freaking out over 6.131 lab

Edit 10/17/2011: Found it! Thanks to Charles.

See explanation of “tilt sensors,” which include both mercury and rolling-ball type ones, here: http://www.ladyada.net/learn/sensors/tilt.html

http://www.adafruit.com/products/173

Cost: $2.00.
(octopart search: http://octopart.com/partsearch/#search/requestData&q=tilt+switch&rangedfilters%5Bavg_price%5D%5Bmin%5D=0.54&rangedfilters%5Bavg_price%5D%5Bmax%5D=2 can maybe get it for $1)
http://smparts.com/-Switches-Rolling-ball-switches-%28AT%29/c0_2_561/index.html — but no prices listed, hah.

Hmm. So I know there was at least one previous design in 2.008 that used these switches. They put two on each side (top and bottom), facing outwards. Then, when the yo-yo spun, both switches would contact (and presumably switch on LEDs). Apparently they had issues with the thermoform shrinking and squeezing the ball switch and preventing it from switching though. All in all, I’m a bit iffy about these rolling ball switches. There’s no way to adjust their sensitivity (although I guess regardless PoV yoyo requires a microcontroller anyway, but the less pin-count the better), so what if it switches on when the the switches are rotated to (left right) and the yo-yo is slightly tilted? We’d be stuck with 100 useless switches.

I like Paulina Mustafa’s design of a flexure switch, she was prototyping this at MITERS (but I can’t find a blog for her). Looks sort of a like a ying-yang design, and the tips are flung outward and make contact with the sides when the yo-yo is spun. She’s using copper-tape, but I think something like conductive glue would be easier to apply.
http://www.instructables.com/id/Conductive-Glue-And-Conductive-Thread-Make-an-LED/step1/Make-Conductive-Glue-Conductive-Paint-and-Conduc/

=====
Earlier Research

via
http://www.helifreak.com/showthread.php?t=33567 “DIY Night Blades”

centrifugal switches:
http://www.atomicmods.com/Categories/Tutorial-1-28-Mini-Z-Rim-Light-Installation.aspx
(spring inside a brass tube)

The batteries are wired in series with the LED and the centrifugal switch. The centrifugal switch is simply a tiny spring inside a brass tube. When you accelerate, the spring swings to the outside and makes contact with the brass tube turning on the lights. It is really quite simple and very reliable. This also makes the batteries last a long time since they are only on while you are driving and you will never forget to turn them off.

types of switches and design of switch contacts (including mercury switch aka “tilt switch”): http://www.allaboutcircuits.com/vol_4/chpt_4/1.html

quora question
http://www.quora.com/Mechanical-Engineering/What-centrifugal-switches-are-suitable-for-use-in-a-yo-yo

still failing to find suppliers o.o

mercury switch:
http://mondo-technology.com/yoyo.html

paperclip style:
http://www.make-digital.com/make/vol22?pg=115#pg117