The Bean: Phone Stand

The Bean is a stand for phones or small tablets. It is composite stone, resembling granite,  cast from a 3D design and a 3D printed master (buck). This page contains extensive details about it’s design, manufacture, and the R & D process I went through to develop it. I have made a small number of copies in stone available for purchase on Etsy. It is also possible to download the master 3D file here and print one out in plastic for yourself. I developed this project to extend the 3D design/printing process into traditional cold casting methods of manufacture. Sufficient detail is provided on this page to cast your own copy of the Bean, although it would not be cost effective to make just one.

Phone stand with a pocket in the back for headphones, etc.
The Bean phone stand with a pocket in the back for headphones, etc.
Acetone fumed ABS 3D printed buck, silicone mold in 3D holder, and final product in cold-cast composite stone.
Acetone fumed ABS 3D printed buck, silicone mold in 3D printed holder, and final product in cold-cast composite stone.

 

After listing the resources I have to share and the basic materials and tools needed to made composite stone copies. I review the process to create copies (and share my failures encountered along the way) and a detailed video covering the casting and finishing process below. I have also included a small gallery of additional photos at the bottom of the page.

Online Resources

A zip file is available that contains the 3D file for the Bean, the 3D mold holder, and a 2D template for cutting a rubber bottom.

Materials

    • A3D printed master (buck).
    • A 3D printed mold holder.
    • Cardboard and glue gun to mount the buck and mold holder.
    • Silicone casting rubber for the mold. I purchased a 1 pound container of Alumilite High Strength 3 Liquid Mold Making Rubber. With the buck and mold holder I created, I used approximately 12oz of the rubber to create the mold. The mold held up well for casting all 10 of the phone stands.
    • A small amount of mineral oil for a mold release
    • Epoxy for casting. I used 80 grams per phone stand. For the batch of 10 I made I purchased a  Clearcast 7000 32 oz kit and had a tiny bit left over.
    • Stone & Sand. Each phone stand contains:
      • 210 grams (60% of the stone mix) Sandtastik Light Silver Floral Sand.
      • 87 grams (25%) Sandtastik Black Floral Sand, and
      • 53 grams (15%) Crushed marble, specifically Fredrix Powdered Marble Dust, which comes in 4 lb bags, so I have a lot left over.
      • Additionally, a few flakes of gold mica are added to the mold before pouring. I purchased a 1 oz container from Amazon and barely made a dent in it.
    • Adhesive backed Neoprene rubber in 0.032″ thickness for the bottom. I purchased 12″x12″ sheets from Amazon.
    • Finishing tools and materials. I used a Dremel tool with a stone grinding bit, followed by 80 grit sanding cloth, and 600 grit wet/dry emery cloth to prepare for a final finish coat. I found that Valspar clear sealer in satin provided the slightly textured clear finish I wanted.

My Experience & Process

The project started with basic design work using Tinkercad, a 3D printer, and a pile of phones and small tablets.

The Bean is consists of 3 shapes. The primary shape is a sphere that has been distorted into a bean shape. The built-in sphere object in Tinkercad has too low of a polygon count to produce a smooth surface at this size. In fact, I used the built-in sphere to start and even cast one copy from that before starting over by importing a much higher resolution sphere primitive into Tinkercad. The front rest shape is an angled rectangular cube with a rounded edge and the back pocket is a flattened paraboloid. These shapes were selected with both final function and ease of pulling from a mold in mind. Much experimentation took place via 3D test prints with regard to overall size, size and angle of the main rest, and height of the lip with a variety of phones (in and out of cases) and small tablets before settling on the final design

3D model of the phone stand.
3D model of the phone stand.

 

Once a final shape was selected I experimented with the mix of material to get the look I sought. I used a piece of weathered natural granite as a model. Rather than repeatedly casting the piece full size and wasting a lot of material in the process, I created a group of very small molds with shapes similar to the final product and cast stone/epoxy mixtures directly into them using vaseline as a mold release.

Some of the small 3D printed models used for testing stone mixtures.
Some of the small 3D printed models used for testing stone mixtures.

 

The biggest challenge turn out to be preventing the result from coming out quite dull. I started with gray and white sand. The white sand just disappeared into the epoxy when cast–I assume it became optically clear. Switching to silver colored sand and adding some white marble dust was the cure. Along the way I found that a lesser quantity of black sand produced a better result than a greater quantity of gray sand. The final mixtures are detailed under Materials at the top of this page.

Another realm of experimentation was the ratio of epoxy to stone mix. The mixture had to be thin enough to work into the tight places in the mold, but think enough that the epoxy didn’t separate out. In fact the addition of the marble powder made the ratio quite critical. The powder is a very fine dust which not only gets everywhere (wear a dusk mask when working with it), but also wants to readily separate from the sand when enough liquid epoxy is available to do so, as is illustrated by a failed experiment.

A bad result in casting. Too much epoxy caused the marble powder to separate from the sand and the rigid 3D printed mold would not release the casting.
A bad result in casting. Too much epoxy caused the marble powder to separate from the sand and the rigid 3D printed mold would not release the casting.

 

My success in pulling casts from the small 3D printed molds led me to think that I could use a 3D printed, two part, full-sized mold for the final pieces.

A 3D printed, two-part mold. This did not work, it was too rigid yet insufficiently smooth on the inside.
A 3D printed, two-part mold. This did not work, it was too rigid yet insufficiently smooth on the inside.

 

The two part mold seemed like a good idea at the time because it would cut out a step of creating a silicone mold. However the rigid 3D printed mold just didn’t work with a full-sized cast. In addition to having no flex, the layers lines from 3D printing trapped the cast material, even with a thick layer of vaseline between.

So it was back to traditional silicone mold making. However silicone is expensive, and it needs a support surrounding it. So I used the 3D model of the buck to created a mold holder, leaving space for the silicone to between the two. This was a very roughly assembled 3D model because it would not be part of the final product, and a fairly large model to print out.

The 3D printed mold holder. ample holes were included for pouring and venting the liquid silicone.
The 3D printed mold holder. Ample holes were included for pouring and venting the liquid silicone.

 

Before molding the buck I wanted to get it as smooth as possible. I printed it in ABS plastic on a high end printer. Then I used the acetone fuming technique and bit of sanding to erase all the evidence of printed layers. ABS plastic is dissolved by acetone, so it can be smoothed with acetone fumes. Acetone fumes are VERY BAD for your lungs and eyes, in addition to your skin. This is a DANGEROUS technique and requires appropriate precautions, namely wearing a respirator (not a dusk mask, a real respirator), rubber gloves, and eye protection. Long sleeves are also  good idea and this needs to be done outdoors or under a proper fume hood.

The ABS model is mounted on a metal stand that can be retrieved without touching the model inside a crock pot (not the one you are making chili in later, I use a dedicated pot for this). A small amount (a couple of tablespoons) of 100% acetone is poured in the bottom and the pot is warmed up with a tightly closed lid. It depends on the model and the amount of smoothing you want, but about 10 minutes of vapor visibly condensing on the inside of the glass lid is enough. If you over do it you will get drips on your model or even melt through the outer shell. The dangerous part is pulling the lid off. Do NOT have your face anywhere near the lid when you take it off, even with a respirator and eye protection on (and make sure they are on). Lift it off at arm’s length and let those nasty fumes blow away. The surface of your model with be very sticky so do not let anything touch it. It will take up to 60 minutes for the surface to fully harden again before you touch it or bring it inside. Several hours should elapse before any sanding takes place. The acetone will probably be all evaporated but wash out the crock pot anyway before you remove your gloves or bring it in.

The 3D printed master buck for casting. This was done in ABS and then fumed with acetone and lightly sanded.
The 3D printed master buck for casting. This was done in ABS and then fumed with acetone and lightly sanded.

 

I don’t have extensive pictures or video of casting the silicone, but it was a pretty straightforward process. The finished buck is hot-melt glued to a piece of smooth, high quality cardboard. Having switched to mineral oil for a mold release, a thin coat of that is added to the buck. The 3D printed mold holder is spritzed with mineral oil and placed (upside down from the orientation it was printed in) over the buck. Make sure there is the maximum amount of clearance possible between the mold holder and the buck all the way around. The mold holder is hot-melt glued down to the cardboard around the outside. The glue seal needs to be liquid silicone-tight, so glue it carefully but use lots of glue. The silicone mold making material is mixed according to the manufacturers instructions and pour into the mold holder per the manufacturers instructions. You have ample working time to get all the air bubbles out. ANY flaws where the silicone meets the buck will be visible in the final casts.

bean mold in holder
Buck and mold holder positioned to accept silicone pour (they are not glued down in this illustration).

After the silicone has cured per the manufactures instructions the assembly can be taken apart. I found that a chisel worked by hand works best to slice off the thick layers of hot-melt glue holding the mold holder to the cardboard. The cardboard can be pulled off the mold. Slide the silicone mold (with the buck still inside) out of the mold holder. Peel back the silicone mold and slide the buck out of it. The Alumilite #3 casting silicone I used is very soft and the buck (and later castings) came out with no drama and to tearing. For casting the phone stands, the silicone mold goes back in the mold holder.

The silicone mold in its holder.
The silicone mold in its holder, ready for casting a phone stand.

 

I recorded a detailed (30 minute) video of the rest of the process. The video covers casting a phone stand in stone using the silicone mold in the mold holder, removing the cast, and finishing it off.

After the stands were covered with a top coat, a thin neoprene rubber bottom was attached. The bottoms we cut on a craft cutter using the shape included in the .zip file at the top of the page.

Gallery

A close up of the grain and mica flakes.
A close up of the grain and mica flakes.
The final satin finish has some texture and a few pores. but is smooth enough not to scratch.
The final satin finish has some texture and a few pores. but is smooth enough not to scratch.
The bottom is covered by a thin sheet of neoprene rubber.
The bottom is covered by a thin sheet of neoprene rubber.
Bean video
Great for watching videos.
The stand can handle a small tablet, but is unstable with anything over 8".
The stand can handle a small tablet, but is unstable with anything over 8″.
The final product weighs just under a pound.
The final product weighs just under a pound.
Product photography by Martha Ball.
Product photography by Martha Ball.

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