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How to make a physical city model on scale

3D relief city models of Venice and Berlin, in wood

DeskProto user Architekturmodelle - Werner (Germany) produces very complex models for urban development design projects and for various exhibition purposes. A great example is the model shown on this page: the complete city of Venice, on scale 1:5000.
The STL file used is 25 MB large, and contains over 500.000 facets.

Top view of the Venice model
City-Relief of Venice, Italy, by Architecturmodelle Werner.

This model will be even more special for you in case you have actually been there: many of you will have visited Venice and will be able to recognize many famous landmarks like the Piazza San Marco. The detail view below shows this square more clearly

Detail view (San Marco) of the Venice model
The San Marco Square in Venice.

To create a very detailed model like this it is needed to use a very thin cutter. As removing all material with such small cutter would take very long, it is best to first use a thicker cutter for roughing.
So this is a good example project to show how combining various cutters and various strategies can be done in DeskProto. In order to do so we have machined the centre part of Venice, and will show all steps taken.

Screenshot with roughing toolpaths
Roughing being done
Left roughing toolpaths, right roughing being done on the machine - 6 mm cutter.

In DeskProto, what will be machined is defined as a Part, using the Part Parameters. How it will be machined is defined in the Operation Parameters. For Roughing and Finishing it is needed to use two different operations within one part. For this model as many as seven operations have been used: roughing, semi-roughing, finishing, several detailing operations, and finally a 2D operation to engrave the text.

Screenshot with semi-roughing toolpaths for San Marco square
Semi-roughing being done
Left semi-rough toolpaths (detail), right semi-roughing on the machine - 3 mm cutter.

The first operation (roughing) has been done with a 6 mm diameter flat cutter. Distance between the toolpaths 1.6 mm, and (important!) a skin of 1 mm thick. As the model is very low layers were not needed. See the first two pictures, total machining time ca 30 min.
After that a semi-roughing operation with a 3 mm diameter flat cutter. Toolpath distance 0.33 mm, no skin or layers used. See the two pictures just above. Total machining time for this operation was 2 hours 43 min.

Screenshot with waterline toolpaths, detail
Screenshot with waterline toolpaths at water level
Left waterline roughing toolpaths, right toolpaths on the city's real waterline.

All subsequent operations have been done with a 1 mm diameter ballnose cutter (the thinnest that we had available at the time). Ballnose in order to get smooth sloping rooftop surfaces.
First a series of Top-to-Bottom waterlines at a waterline distance of 1 mm (the picture above left): a thin cutter like this cannot machine a small street at full depth in one go. That was the most time consuming operation: total machining time 8 hours 17 min.
Next a parallel finishing operation has been done, to remove the staircases left by the previous waterlines. Toolpath distance 0.2 mm. Again a very long toolpath: machining time 7.5 hours.
After that two detailing operations using waterlines: one just below rooftop level, in order to make the very small streets (too small for this cutter) visible as a groove, and one at water-level to create a smooth waterfront contour (the picture above right: a real waterline !)

The resulting scale model of Venice center
The resulting partial model of Venice, in tooling board, size 250 x 200 mm.

The final operation was to engrave the "Courtesy of ..."" text in the sea at the right side of the model. A 2D operation, with a 2D DXF file created in Rhino.

The total machining time for this model has been very high: this is not typical for DeskProto (Rapid Prototyping). Still as shown here DeskProto can do very detailed models as well.
Note that in the picture above you can clearly see some differences with the master's hand (Architecturmodelle Werner): the original model shown at the top of this page is far more detailed than our own model.

Very large relief model of the city of Berlin
Wooden relief city model of Berlin.

A second model to show the hand of the master: Architekturmodelle Werner also produced the very large city model of Berlin shown above. This scale 1:5000 city model is on display in the Staatsbibliothek zu Berlin (Berlin State Library), in the cartography section.