There are many ways to make screw threads in SketchUp. Here is one more using the Spirix plugin …
One of the aspects of SketchUp that makes circular objects such an issue in 3D printing is the use of line segments to approximate an arc. This is glossed over by the visual smoothing functions that make even relatively crude circles look smooth. While this is fine for visual aids and drawings, any circular arcs that will be 3D printed will need many more line segments than usual. However, this is not a problem if you are only making a single part here and there. A complete car with all of its mechanical details, for example, would not only be a very large model, but it would also not be suitable for 3D printing in the first place.
As an example, I chose to make a large 1" bolt about 2" long with an ACME screw thread. I also deliberately used 400 segments for each circle to show that oodles of points is not a problem (100 would have been more than enough). As per the usual SketchUp caveats, I constructed everything at 1000x scale.
I started by creating a profile of the thread I wanted and grouped the lines:
I traced around the trapezoid to form a closed loop:
Then I used the Spirix “Create Surface” function to create one revolution around the Z-axis while “rising” 0.140" (140 @ scale). Note that I specified 400 segments for this operation:
I then edited the resultant screw thread to “heal” both ends of the thread (this seals it and makes it water-tight):
I then made the group into a component and replicated it 20 times:
In order to create the body of the bolt, I added a circle at the base of the first thread (using 400 segments) and extruded it up to the bottom of the top thread using the Push/Pull tool and grouped it:
To add a hex head to the bolt, I created a hexagon from the center of the cylinder (note the interference patterns):
Extruding this with the Push/Pull tool and grouping it gives the final bolt:
In order to reduce the cost of printing this, I used the Offset and Push/Pull tools to inset the hex head and did the same with the cylinder from the bottom:
Using MeshLab to inspect it shows more visual interference, but this is no cause for alarm since each component is water-tight in its own right:
There is somewhere on the order of 50,000 polygons in this model, but the use of a component reduces the actual size quite a bit. The exported DAE file is only 660KB and the model file itself is only 604KB (see attached). However, when I uploaded the file to a 3D printing firm, it took quite a long long while for its slicer to digest it, but it finally gave their stamp of approval:
As I pointed out earlier, 400 points for a 1" diameter circle is way way overkill. But it illustrates the point that using a plethora of edges is not necessarily difficult to do when approached appropriately. As for performance issues, this was all done in less than 10 minutes on a netbook with an Atom processor and 1GB of memory running Windows 7 Home Premium and SketchUp 8.
Bolt model in SketchUp 8 format: bolt.skp (603.0 KB)
Spirix plugin: https://sites.google.com/site/spirixcode/code/spirix.rb
