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How to CNC machine a car model on scale

Machining a scale model of a Ford Capri vintage car

DeskProto user PROTOway in Porcia (Italy) offers a full range prototyping services:
- Aesthetic models in wood, polystirol or resin,
- Functional prototypes, transparent, water resistant, high temperature proof, usable in any field.
These models are made using CNC milling, Selective Laser Sintering (SLS), Stereolithography (SLA), combined with a variety of traditional techniques.

Screenshot of the 3D CAD model
Detail: polygons drawn as wireframes
CAD model in Rhino: rendered (L) and as polygons (R).

This project concerns a scale model of a vintage car, to be used for a trade fair. The Ford Capri was a very successful "pony car", produced by Ford Europe from 1969 to 1986.
The model is a solid block model in PolyStyrene foam, total length 1200 mm, done with DeskProto on a three axes router. As you can see in the picture above the 3D geometry for this model has been obtained by reverse engineering (3D scanning), done by Digi.Lab in Rome. Size of the resulting STL file was 110 MB.

Hand that holds a small STL model
Small scale model of the Ford Capri, made using Protoway's stereolithography machine.

First the geometry file has been used to create a small model (scale 1:18) on a stereolithography machine: see the picture. This is a great technique for a small, thin-walled model like this, however in other cases CNC milling is better suited. Like for a large model, a solid block model, a specific material, a special finishing method, or in case the STL file is not watertight.

DP screenshot with toolpaths for left side panel with car door
DP screenshot with toolpaths: detail with head lights
DeskProto toolpaths for some of the 14 parts.

Milling has been done on PROTOway's custom made router of 1750 x 900 x 250 mm, with an ELTE spindle. As this is a three axis machine the model has been constructed by machining a number of separate parts. 8 parts have been created: two parts for each side, plus front, rear, roof and spoiler. Total machining time was about 18 hours.

The CNC machine in action, milling PolyStyrene foam
Two machined parts are glued together and filler is added where needed
Milling foam on the CNC machine (L), and assembling some of the parts (R).

As you can see in the picture above a powerful vacuum-dusting system is important when machining PolyStyrene foam.
These parts have then been manually assembled to create the complete model: a sort of "box" with the external faces machined and a hollow inside.

Hands that are smoothing the resulting model
Manually finishing the assembled model.

After assembly some manual finishing (sanding) was needed to remove glue residue at the seams. Also filler is added where needed, followed by sanding the surface. It is amazing to see what a skilled model maker like PROTOway can achieve using a lowcost material like PolyStyrene.

Detail view of the front of the car
Partial view of the front of the model, showing a number of nice small details.

The resulting model in my view is great: it exactly shows the car as I remember it (from a very long time ago ...). Unfortunately the fair for which the model was meant has been cancelled, so the model has not (yet) been finished by spraying it in the correct colors and adding wheels, fenders and smaller details.

The resulting Capri model in PolyStyrene
The resulting model of the Capri. The model has not yet been painted