Darryl Dennis

Hobby projects ect.

Splitting a complicated model


I am hoping someone may be able to help me with a solution to a design issue I am trying to address. I have developed a 3D printable model of what could be described as a celestial sphere. This project may be somewhat unique because the actual model drawings are not produced in Fusion 360 or any other CAD drawing tools.  I have used OpenSCAD code that takes star location data from star and constellation tables to produce a STL file model. The resulting 3D model is a scale representation of the  locations of hundreds of the brightest stars as well as connecting lines that indicate shapes of the celestial constellations. The OpenSCAD files produced STL work well and allow for the capability of doing a dual extruder 3D print where the consolations lines are printed in one color while the background sky is printer in another color. See my Thingiverse page for more detail  https://www.thingiverse.com/thing:4783219

I would like to print a larger version of the celestial sphere then my printer can do in one piece.  Ideally, I would like to split the print into as many as 9 separate pieces that can be mounted together to produce one large model. There are several factors that make this simple split quite difficult to achieve with satisfactory results.  The finished model will be displayed with a bright light source inside the sphere. The relative star brightness will be represented by the relative size of the hole through the sphere. The constellation lines will be represented by thin lines on the surface of the sphere between appropriate stars. The OpenSCAD code produces an accurate and detailed model, but the actual sphere is not a nice even curved sphere, but a fragmented representation of a sphere made up of many flat surfaces. It is important to maintain the integrity, location, and size of all the features within the original model, even when these features are very close to or extend across a break that may have occurred between adjacent pieces of the large model.  In order to reduce the perceptibility of the split locations on the large model there should be no straight-line connection between adjacent pieces. Some type of overlapping connection would be ideal. A tongue and groove or shiplap type split connection would reduce the possibility of light showing along the splits. 

In fact, there are two separate but very closely related files produced to print this model, one for each extruder on the 3D printer. One file models the background sky with the star locations holes located in the appropriate spots and the other models the constellation lines that protrude slightly from the surface of the sphere in a different color. 

I should possibly split the model in the OpenSCAD environment and the develop code to model some type of overlapping joints while maintaining the integrity of the detail within the model. That approach has its own issues and may not be simple or straight forward.

I thought that I could likely split the models using Fusion 360 and print the individual 3D printed segments. This plan has turned out to be much more challenging than I anticipated. I can import the STL files into Fusion. I can covert the MESH models into solids in fusion 360 models.  The result is one Body for the background sphere model and  444 bodies representing the individual constellation lines in that model. I can split the models along straight lines, i.e. a northern cap piece representing the sky North of 60 degrees latitude. Eight wedge shaped pieces each representing a 45-degree slice to the sky. There are several issues that I run into at this point. Producing an overlapping joint at these split locations without losing any detail in the model (holes or lines) is proving difficult. Identifying, spitting and cataloging which of the 400 + constellation line bodies are fully or partially  on any of the 9 separate pieces is near impossible.

I realize I am trying to accomplish a considerable amount.  In order to achieve what I have in mind I will have to convert the two models that I am importing as STL file into 18 separately printable models that is 9 segments of the original model each having two parts one for each of the two printer extruders. That must be achieved without losing any detail on overlapping split joints or losing perfect alignment of the models to each other.      


At this point I am thinking about ways to achieve this result in OpenSCAD, or perhaps split the model in OpenSCAD then import as 18 files and somehow produce the overlapping joints in fusion 360 or perhaps forget about using fusion 360 for this operation.

I could post pictures of files if anyone is interested.

I would greatly appreciate any ideas or approaches that I may have overlooked.