Boston model 19 replacement reduction gear

We had an old Boston model 19 sharpener that didn't work anymore. After a brief and easy disassembly (which somewhat reminded me about how much better old and simple devices used to be) I found a gear with many shredded teeth that was a reducer for the high-speed single-phase AC shaded-pole motor.

Thankfully these motors are pretty easy on plastic gears, even PETG (though Nylon or PC would work better.) The original plastic gear likely gave out due to age. In my infinite wisdom, however, I didn't bother to check if anyone else had cloned this gear, so I measured and modeled in FreeCAD a gear with:

• 70 teeth

• OD of 53.65mm

• Transverse module 0.745

• Helix angle -5.6 degrees

Tested in PETG now that I got my satin sheet, and works well. I also used some of the Prusa lubricant on the gear assembly to hopefully reduce future wear. Only after I had prepared this post did I discover that my work was redundant, but I still figured I'd upload this project here anyways, since I can provide more technical data as well as original CAD files for the community.

I will update the post over time to report on reliability. Sharpen away.

Includes a 3MF PrusaSlicer project with the following settings. These are recommended for best fit and reliability over time.

• Generic PETG

• 0.15mm Structural

• 60% gyroid infill

• 101% scale for X/Y axes

• 6 bottom/top solid layers and perimeters

• No supports

• Prusa CORE One, 0.4mm HF nozzle

Also includes a print file with the above settings.

Additional model files are included in other formats for you to modify and use.