Yay! New 3D printer arrived!
In order to justify the purchase, I need to make sure that the machine actually saves me money in the long run. My paper shredder broke just a week prior to getting the 3D printer and is now a good candidate for the project. I paid $5 for it at a thrift store, but the replacement part costs at least $30 plus shipping.
How did I break it? Well, let's just say the size of the slot where you insert the paper is a bad indicator for how many sheets of paper you should feed it. Long story short, it made a strange noise and the shredding cylinders stopped rotating despite the motor seems to be spinning just find. Taking the shredder apart reveals a broken compound gear. I measured the outside diameter of the gear and calculated the approximate pitch diameter based on the number of teeth and made the gear in CAD, as shown in the picture below.
After a few trial prints (one half-height piece for section of the compound gear) to confirm the fit was good, a full sizes part was then printed. The picture below shows the 3D printed part next to (what was left) of the original part. The final gear geometry deviates a little from the calculated values. Significant adjustment was needed for the smaller portion of the gear. The final gear geometry which yielded a good part is included at the end of this post.
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| Left - original part (broken); Right - 3D printed replacement |
The tolerance of the printed part seems to be pretty good. The shaft measured 0.172", and I made the hold diameter 0.19" in the CAD model. The printed hole size was 0.177", which gave me a pretty nice slip fit. All measurements are taken without considering the first layer of the printed part, where the bead of material is flattened a little more than the rest of the layers thus resulting a slightly wider line. This is easily fixed post printing by pushing a screw driver (with a Phillip tip that's slightly larger than the hole) against the first layer of the hole and giving it a few twists. The pictures below shows the printed part in action.
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| 3D printed part in action |
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| A close up |
I just spent an afternoon and saved myself about 30 bucks. If I do this another nine times I might actually recover the cost of the 3D printer. Too bad I don't have anything broken at the moment. The model of the paper shredder is Fellowes P-57Cs. You can find the part here on
Thingiverse.
Gear Geometry
| FINAL DESIGN VALUES for Large Gear | | FINAL DESIGN VALUES for Small Gear | |
|---|
| Outside Diameter (in) | 2.000 | Outside Diameter (in) | 0.750 |
| Num of Teeth | 40.000 | Num of Teeth | 7.000 |
| Height (in) | 0.475 | Height (in) | 0.550 |
| Diametral Pitch (teeth/in) (approx) | 21.000 | Diametral Pitch (teeth/in) (approx) | 12.663 |
| Pitch Diameter (in) | 1.905 | Pitch Diameter (in) | 0.553 |
| Clearance (in) | 0.010 | Clearance (in) | 0.020 |
| Hole Dia (in) | 0.195 | Hole Dia (in) | 0.195 |
| Pressure Angle (deg) | 14.5 | Pressure Angle (deg) | 20.0 |
