How to create a mother model for silicone chocolate forms
A chocolate cow bar in various colorsDeskProto user The Chocolate Chisel in Wisconsin (USA) offers specialty chocolates, both from stock and custom made following the client's design.
Chocolate products created by The Chocolate Chisel.
Most of these products have been created using CAD/CAM technology: designed in CAD, mother model machined in wax on a CNC milling machine, the production mold created by pouring silicone over this mother model. Chocolatier John Reichert has ample experience using these tools, both for chocolate molds and for other applications.
The steps of this production process will be illustrated below, for a chocolate bar that features a well-known Wisconsin ("America's Dairyland") representative.
The separate 3D building blocks in Rhino CAD (this is the Mac version).
The design of this Wisconsin chocolate bar has been created in the Rhino 3D CAD software. In Rhino it is easy to create 3D characters, and so is designing the curved 'ground' where the cow will stand on. The geometry of the cow has been scanned from an original sculpture using a Roland Picza piezo 3D scanner at .002" resolution, and has been transferred to Rhino using an stl file.
All these building blocks have been correctly scaled and positioned in Rhino, and the resulting assembly has been exported as STL file. You need not worry about possible small gaps in the STL geometry, or about surfaces without thickness: DeskProto does not care about such formal errors.
The STL file loaded in DeskProto.
Now in DeskProto it is very easy to import this STL and then create toolpaths.
John Reichert states: "I open the STL in DeskProto and then determine what endmills and strategy to use. Once I have determined my settings DeskProto writes the G-code for me".
Two different cutters have been used: for the roughing stage a .125 inch ball nose cutter, and for finishing a tapered cutter (V-shape) with a .003 inch flat tip. Strategy was parallel toolpaths along the X axis, stepover (distance between the toolpaths) .041 inch for roughing and .0015 inch for finishing. When roughing a .0156 inch skin was left over the surface.
The mother model is machined in Wax, on a Taig machine.
As the image above shows, a positive model (so identical to the designed chocolate bar) is then machined in wax: the mother model.
Milling has been done on a Taig desktop cnc machine. Roughing took about 30 minutes at 30 ipm (inch per minute); Finishing took 4-6 hours at 15-20 ipm, with a 11,000 rpm spindlespeed (for this small tip a high spindlespeed is needed).
The mold has been created by pouring silicone over the wax mother model.
For the production of the actual chocolate bars a mold is needed (so a "negative" of the bar). This can be created by pouring silicone rubber over the model: after curing a (flexible) mold will be the result. It is clear that for this application a "food grade" silicone needs to be used, so a rubber type that has been approved for the production of food. The silicone rubber used is Smooth-On Smooth-Sil 940 food safe.
The resulting bar, in three types of chocolate (dark, milk and white).
As you can imagine the production process of this bar is more complicated than just filling the mold with molten chocolate. Various types of chocolate have been used to achieve the desired coloring scheme: dark chocolate, milk chocolate and white chocolate. The green color has been achieved by air brushing the mold with naturally pigmented cocoa butter.
The size of the bar is 7.5"x4.5" and it weighs one pound.
Two artworks by John Reichert, CNC machined in wood.
The artist behind the Chocolate Chisel, John Reichert, also creates carvings in wood, see the images above. The same cow geometry has been used for a large sculpture in Jelutong wood, made for the Babcock Hall school of dairy in Madison WI. In addition he also manufactures a line of pewter artwork. For more information see his website www.reichertstudios.com.