Many of the changes made as the design evolved focused on attempting to achieve smooth motion of the slider along the helically shaped path. A first decision was whether to have the slider rail be an extrusion from the lower arm plate (Figure 1) or a helically shaped bar attached to the lower arm plate (Figure 2). Using a rod would allow a harder rail for the slider than an extruded rail made from 3d printed ABS (acrylonitrile butadiene styrene) or PLA (polylactic acid), and this would be advantageous. A specialized a freeform pipe bending CNC machine are capable of complicated pipe bending could theoretically be used for making the bar, however we did not have one available for our use and we wanted to produce our design with the means available to us. Another possibility discussed was the use of a hand bending tool or roller. The problem with bending tools is that they can only make 2-dimensional bends of a certain radius. A roller would allow more flexibility in the radius of the curve made, but again is designed for making a 2-dimensional bend. The technique attempted was the constructing a custom cylindrical jig sized for the curve being made and hand bending the rod round the jig, as shown in Figure 3. Using this method we were able to bend a piece of 5/16” steel rod into an approximately helical shape. However this was technique was unable to achieve a sufficiently accurate curve, so the decision was made to print the rail.
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