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How to CNC machine a cookie mold in wood

A logo was converted to a relief and used as a mold for cookies

DeskProto user Marcel is an enthusiastic CNC evangelist. His company RoboCNC (website partially in Dutch) not only offers CNC services, the website also shares experiences about machine building and offers videos on a wide variety of CNC related projects.

This Gallery page is about one of these video projects, where Marcel CNC machined a wooden mold for baking custom designed cookies. Marcel's idea was to use the icon in his company logo. When that 2D logo could be converted to a 3D relief it would be possible to machine it as a 3D shape. Creating such reliefs is the specialism of Todd Bailey of 4M3D, who was able to create the desired 3D shape and deliver it as STL file.

The RoboCNC company logo (2D)
The logo converted to a 3D relief
The RoboCNC logo icon in 2D and the 3D relief created by 4M3D.

"Speculaas" is special type of cookie, very popular in the Netherlands, traditionally made in a relief shape like a costumed figure or a windmill. Imagine a special sort of Gingerbread man. Interesting detail is the (ancient) original meaning of such figure cookies, which is an offering to the gods: better burn a cow-shaped bread - or cookie - then sacrifice the real cow...

The cookies are formed by pressing dough in a wooden mold, in which the shape is present as a cavity. Such wooden mold is called a "Speculaasplank". Traditionally carved by hand, for which nowadays CNC machining is an attractive alternative.

Screenshot of the Cookiemold geometry in DeskProto
Screenshot of the roughing toolpaths
DeskProto screens: first the geometry, next the roughing toolpaths.

The picture above shows the design of the cookie mold to be used: four cavities, each showing the logo icon and some text, as a relief on top of the cookie. All as mirrored images in order to get correct cookies (the word "speculaas" originates from the Latin speculum, which means mirror).

In DeskProto Roughing toolpaths were created for a 6 mm diameter ballnose cutter. Block strategy, 12 mm layer thickness (depth of one roughing pass) and leaving a 0.6 mm skin to be removed when finishing. As you can see the outside vertical surfaces of the mold have not been machined (only the cavities matter), which was done by selecting "No extra"for the Borders.

DP screenshot: finishing toolpaths
DP screenshot: toolpaths for the text
Left the finishing toolpaths, and the toolpaths for the texts.

The Finishing toolpaths were created for a 2 mm diameter ballnose cutter, using a very small stepover (0.12 mm): better have the machine spend some extra time than have to spend your own time on using sandpaper afterwards.

As this cutter was too large to create the (very small) text a third operation with was needed with toolpaths for the text, using a 1 mm diameter ballnose cutter. Cutting the complete mold with this small cutter was not needed, so the area to be machined was limited to only the texts, using a Freeform segment (segment boundaries imported from a DXF file).
In the screenshot above many vertical tool movements are present as conventional cutting was chosen: as Marcel tells in his video (see below) meander would have been more efficient here.

The mold being machined, top view
The mold being machined, side view
Machining the mold in beech wood.

Machining was done on Marcels DIY build RoboCNC X1 router. Material is steamed beech wood, as that is food safe and allows detailed carvings. As you can see an oversized slab of wood has been used: after machining the wooden mold was made on size using a saw.
Total machining time was about 3.5 hours.

The wooden cookie mold
The resulting "Speculaasplank" wooden cookie mold.

After machining the wood was treated with wood oil (a food safe type, meant for cutting-boards).
Other manual labor, like sanding or polishing, was not needed as the machined surface was smooth enough already.

Filling th mold with dough
Flattening the bottom of the cookies
The mold being used: left it, and flattening.

The actual cookie production nevertheless is a manual process: each cavity needs to be filled with dough (apply some flour for easy demolding later on), after which the excess of dough is removed with a large kitchen knife (flattening the bottom side of the cookies). Next each cookie needs to be removed: ready for baking.

Removing a dough form from the mold
A series of unbaked cookies
The unbaked cookies, ready for the oven.

That process can be repeated a number of times, until you have enough (or have ran out of dough :-)
As you can see the filling part is critical: if you do not carefully push the dough into the cavity some details (like here the text) will be lost.

RoboCNC cookie mold video still
Marcel has published a great video about this project on YouTube. Start it by clicking on the picture (11.50 min).

The RoboCNC website contains a great wealth of CNC related videos, all hosted by YouTube. One of these is a video that Marcel made about this Cookie mold project - in fact most illustrations on this Gallery page are screenshots from this video. You can start it by clicking on the arrow picture above.

Two RoboCNC cookies
Preparations for baking some nice Robo Cookies.

The actual cookie baking has not been done by Marcel (not sure whether he does not want to or is not allowed to :-). The resulting cookies are the courtesy of his girlfriend Karin. At the end of his video Marcel concludes that her fresh Robo Cookies do taste great !