I tested every gear I sell. This gear will fit. This gear will work. This gear will outlast the rest of your pencil sharpener. I personally guarantee it. May your pencils be sharp forever!
See this gear in action on Youtube:
How To Fix a Boston Model 18 Pencil Sharpener (Gear Replacement) - YouTube
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I designed this replacement gear for Boston Model 18 pencil sharpeners about 2 years ago when my dad's old gear finally broke. The Boston 18 is a fabulous little machine, it's a pity that the original nylon gear can't keep up with the rest of the device!
Why is this 3D-printed gear superior to the rest?
Because this one was made (by me) out of rugged PETG plastic. You know this material as the type of plastic used to make things like water bottles; so, you know that even a thin film of PETG is super strong (doesn't pop when you drop it down the stairs) and thicker parts are tough enough to hold threads (keeps the cap on when you drop it down the stairs). The primary advantage of PETG is its resilience; its surface is hard to chip or ablate because the polymer structure spreads forces out.
Ever try sanding a water bottle? Well, don't bother because it doesn't really work; PETG plastic stays together. Now, if you try sanding something made of ABS, like a Lego, you'll find that it works pretty well. ABS wears out, that's why ABS is not an long-term solution for gears. And, of course, you could make gears out of PLA and they would make lovely Christmas ornaments, but PLA is far to brittle and susceptible to heat-deformation to be dependable over time.
So, buy this Superior Model 18 gear and you'll only ever need the one. Guaranteed for the life of your pencil sharpener.
The Model 18 gear-teeth feature a mild helical-slant to mate correctly with the original drive-gear (the exact slant is a secret, but it's something like 2 degrees). If you are fresh on your gearbox design principles then you see the genius present here in the original Boston design:
The helical-slant means that the teeth of the drive gear push on the teeth of the other gear in the axial direction as well as causing rotation about that axis. Translation: the motor works to spin the gears (duh) but also the motion of the helical gear-teeth pushes the gears apart; which means--due to the clever design--that the drive gear is continually pushed towards the motor and the other gear is continually pressed against the axle. Why is that good? Because the motor's electromotive force pushes the drive gear back down and YOU (the user) push the axle back in with your pencil! This brilliantly holds everything stable for decades; but, eventually, the old nylon gears succumb to the stress.
The helical-slant means that the teeth of the drive gear push on the teeth of the other gear in the axial direction as well as causing rotation about that axis. Translation: the motor works to spin the gears (duh) but also the motion of the helical gear-teeth pushes the gears apart; which means--due to the clever design--that the drive gear is continually pushed towards the motor and the other gear is continually pressed against the axle. Why is that good? Because the motor's electromotive force pushes the drive gear back down and YOU (the user) push the axle back in with your pencil! This brilliantly holds everything stable for decades; but, eventually, the old nylon gears succumb to the stress.
Why is this 3D-printed gear superior to the rest?
Because this one was made (by me) out of rugged PETG plastic. You know this material as the type of plastic used to make things like water bottles; so, you know that even a thin film of PETG is super strong (doesn't pop when you drop it down the stairs) and thicker parts are tough enough to hold threads (keeps the cap on when you drop it down the stairs). The primary advantage of PETG is its resilience; its surface is hard to chip or ablate because the polymer structure spreads forces out.
Ever try sanding a water bottle? Well, don't bother because it doesn't really work; PETG plastic stays together. Now, if you try sanding something made of ABS, like a Lego, you'll find that it works pretty well. ABS wears out, that's why ABS is not an long-term solution for gears. And, of course, you could make gears out of PLA and they would make lovely Christmas ornaments, but PLA is far to brittle and susceptible to heat-deformation to be dependable over time.
So, buy this Superior Model 18 gear and you'll only ever need the one. Guaranteed for the life of your pencil sharpener.