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A first iteration of the slider mechanism used a 3d printed slider, as shown in Figure 4 below. This apparatus, as expected, resulted in a slider that experienced significant friction. Some sort of linear bearing was needed, but the curvature of the slide rail does not allow the use of a standard linear bushing, such as that shown in Figure 5. A posting on Grabcad, shown in Figure 6, provided an inspiration for a possible solution. Splitting the slider into a front and back piece and allowing some flexibility between the pieces might allow the slider to follow the helically shaped rail. This basic design was attempted in several iterations, shown in figure 7 through figure 9 below. All prototypes used 5mm x 11mm x 4mm bearings. The would and printed PLA parts were held together using nuts and bolts, and the aluminum prototype used 5mm shafts with set screws to hold the pieces together. The PLA sheets were used connect the front and back portions of the aluminum slider.
Figure 4. Printed slider Figure 5. Standard linear bushing Figure 6. Slider design from Grabcad
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The manufacturing of the hinge on the upper arm and the hinge attached to the slider was straightforward with no design changes. Flanged bearings bearings (1/4 ID, 1/2 OD) were inserted into either end of a piece of aluminum and a rod 1/4" steel shaft inserted through holes in the printed PLA pieces, . This was all held together with using a retaining pinclip on the outside of the bearings. A rod between these two hinge pieces was held in place using 1/4" set screws, allowing alteration of the length of the rod and adjustment of the relative angle of the two hinges. These pieces are shown in Figure 12 below.
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