Figure 1: Original sketch of movement 429
The mechanism I chose to recreate for this 2D-drawing assignment was movement 429 from 507 Mechanical Movements (Figure 1). This mechanism is called a double elliptical rotary engine, which operates by having steam flow through a channel and into the system, forcing the gears to rotate in opposite directions.
Figure 2: Movement 429 image trace
I first attempted to use image trace on the sketch itself. I cleaned up the sketch by expanding it, then ungrouping to isolate individual parts. After removing the arrows, numbers, and some imperfections from the trace, this was my final result (Figure 2).
The vector-based version of the sketch is very clean, but it is clear that the gears would not work properly if manufactured from this source file. The dimensions and quality of the gears is not high enough in this sketch for use in assembling the mechanism.
For this reason, I downloaded the animated version of the image and used image trace on it (Figure 3). This image was created with proper dimensions and geometry, so I thought it would be a more reliable source to use with image trace. However, even with the best presets, each image trace had some kind of flaw.
Figure 3: Image trace from animated image
The technical drawing image trace produced a sketch with nice, sharp edges in most places, with some inconsistency. For example, you can see that some teeth are more curved than others. In addition, there are some areas where the trace is a bit jagged. The silhouette option produced a clean sketch with more rounded teeth than those in the technical drawing. However, there were some areas with fill that needed to be removed. Lastly, the low fidelity image option produced a sketch that accurately recreated the shapes and contours of the image but with lots of gaps in the trace. I believe that any of these image traces could have been tweaked to be useful as a template for laser-cutting the parts; however, I chose to recreate the gears from scratch, using these sketches as a template.
I achieved this by using the shape tools in Adobe Illustrator to create simple shapes that approximated individual parts of each gear. For example, I used rectangles as teeth and circles as the gear body. I then used the free transform tool and the direct selection tool to move individual points and create more accurate shapes. Lastly, I used the pathfinder tool to combine these shapes, either subtracting common area away or unifying the objects (Figure 4).
Figure 4: Rebuilding parts with pathfinder
Lastly, I needed to recreate the frame of the mechanism. I did this using the curved rectangle tool and circle tool to create the basic shapes, then the pathfinder, pen, and curvature tools to unify and tweak the shapes. My final drawing is shown below (Figure 5).
Figure 5: Final drawing of double-elliptical rotary engine
This drawing is a close approximation of the original mechanism. My primary concerns are with the spacing and length of the gear teeth, but I think that the parts will be functional, provided the laser kerf does not significantly affect the size of the parts. It was challenging to recreate the exact geometry and dimensions of the gears from scratch, so if I did this again, I would attempt to fix the imperfections of one of the image traces. I think that might provide better results.
It is also important to note that the channel running through the upper and lower shaft of the frame was not included in the drawing. This cannot be manufactured using a laser cutter, as it is a 3-dimensional feature that runs through the frame. It will be necessary to add this channel some other way, such as with a drill.
Figure 6: Double-elliptical rotary engine parts
These parts (Figure 6) are available to
download as an Adobe Illustrator project file.
Check it out here!
