Having been fascinated by planetariums and planetarium projectors since I was a kid growing up in the Bronx, I wanted to have a table top model of what I remember seeing at the Hayden planetarium in the 1960s and 70s.

Not finding anything available to purchase, I decided to make my own.

I'm not sure when the Hayden planetarium converted their model II to a model III, but I settled on the model II for the 3D printed model, as it just looks better to me than the III, with the square base and ruff.

SOFTWARE
I built the model using a combination of CAD/3D modeling software. The main 3d modeling was done in AutoCAD. Post processing and conversion to the 3D printable (.stl) format was done using 3D Studio Max. Final processing was done using Netfab. Further processing was done by Shapeways (the 3D printing service) where necessary.

SCALE
I always build my models at actual size and print at the desired scale. For the Zeiss model II, it was pretty clear from the start that the planet cage support struts were probably going to be the deciding factor in terms of minimal part thickness. As it turned out, there were other, finer parts that would also contribute to the decision to go with the 1=7 scale (I refer to this scale as 3.5", as that's what the diameter of the star balls are).

REFERENCE MATERIALS
One of the most enjoyable parts of modeling objects like this is the research involved. The lowest hanging fruit in this respect was searching for photographs on google. I found a really good image that had, what I assume was, the then director of the Hayden planetarium standing below the instrument.

This was a good shot as it showed the planetarium projector from the side, with a person of known height (I assumed he was 6' tall) for a scale reference. Since the model was going to be 3D printed at the smallest possible scale, it really didn't matter if the scale reference was accurate. The idea is that all of the dimensions are correct relative to each other.
One of the techniques I use, is to lay an architectural scale down on a known object (in this case the director at 6'-0") and establish a relative scale multiplier for subsequent measurement of the other components.

Another technique is to insert photos into the AutoCAD drawing, adjust the scaling and orientation as needed and then draw over the top of the photo.

Books were another great resource. I found several that explained the workings of the Zeiss planetarium projector. The best of these,"From the Aratus Globe to the Zeiss Planetarium", by Helmut Werner, had great photographs as well as drawings and explained the history of the Zeiss planetarium projector and related instruments.

Here's the original 3D print with the new, 2/3 scale version.

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