Drive Gear for Model 17 Pencil Sharpener

thingiverse

My wife recently found a Boston Model 17 pencil sharpener that was missing its shaving tray. After printing a new tray online (http://www.thingiverse.com/thing:672194), the drive gear suddenly broke down. I searched the web and discovered this is a common failure with this particular model. I tried printing a gear based on designs posted by others (Thingiverse #267626 & #499349) but unfortunately, my pencil sharpener transitions from a slotted key to a round shaft halfway through the part. Despite attempting to machine the gear to fit, it ended up being too wobbly. Using VariCAD, I completely re-designed the gear and included an oblong key and circular shaft that are integral to the center cylinder. The design also features an inset on the spring clip side similar to the original gear, making it easier to attach the spring clip. A separate test piece is included that is identical to the center cylinder, allowing users to scale it to fit their needs. Scaling should be done within a few percent for best results. I used Taulman Bridge material to print the gear and if ABS is used, scaling may need to be adjusted for shrinkage. The printing settings were as follows: nozzle size 0.35 mm, extrusion temperature 240 C, bed temperature 90 C using a glue stick on the glass, part printed on a raft with support for the gear, layer height 0.2 mm, top and bottom layers 5 each, infill 75%, infill speed 25 mm/s, perimeter speed 13 mm/s, support material speed 30 mm/s, bridge speed 40 mm/s, non-print moves 100 mm/s, first layer speed 80%. I recommend printing the independent center cylinder to adjust scaling and fit; this should be done within a few percent. Once the center cylinder is scaled correctly, you can scale the whole gear by the same amount. Please note that the gear size will have priority over other parameters due to the way the design works. If not exact, close approximation will suffice, allowing users to work with the remaining issues on the cylinder.