Drive Gear for Model 17 Pencil Sharpener

thingiverse

My wife found a Boston Model 17 pencil sharpener missing its shaving tray. After printing a tray (http://www.thingiverse.com/thing:672194), the drive gear broke. Looking on line, it seems this is a common failure for this model. I tried printing a gear that others had posted (Thingiverse #267626 & #499349), but my pencil sharpener transitions from the slotted key to a round shaft half-way through the part. After machining the gear to fit, it was too wobbly. This was completely re-drafted using VariCAD and the oblong key and circular shaft are integral to the center cylinder. It also includes an inset on the spring clip side similar to the original gear to make it easier to get the spring clip attached. I've included a separate test piece that is identical to the center cylinder to allow people to scale to fit, you should be able to scale within a few percent and still have everything fit. The test piece prints out fairly quickly and doesn't use much material, so using it to determine by how much to scale the full gear should go pretty quickly. The gear is 1/32" under-size in diameter (1/64" undersize in radius), so you have a little wiggle room to adjust for shrinkage. See the instructions for more detail Instructions I made the gear using Taulman Bridge material. If you use ABS, you may need to adjust scaling for shrinkage Settings were: 0.35 nozzle 240 C extrusion material, 90 C bed using glue stick on the glass Part was printed on a raft, the gear was printed on a raft with support. 0.2 mm layer height 5 top and 5 bottom layers (I like a thick shell) 75% infill 25 mm/s infill speed 13 mm/s perimeter speed 30 mm/s for support material 40 mm/s for bridges 100 mm/s for non-print moves First layer speed 80% Print the independent center cylinder to adjust scaling to fit; you should be able to scale within a few percent and still have everything fit. After scaling the center cylinder, you can scale the whole gear the same amount. The gear is 1/32" under-size in diameter (1/64" undersize in radius), so you have a little wiggle room to adjust for shrinkage. If not, you can at least come close -- gear size will be the most important parameter and you will have to live with any issues on the cylinder.