Home Made Gears Save This Shredder

It’s very likely that a majority of readers will have had a gear fail in a piece of equipment, causing it to be unrepairable. This is a problem particularly with plastic gears, which shed teeth faster than a child who has discovered the financial returns of the Tooth Fairy.

[BcastLar] has a shredder with a gear that has, well, shredded. He’s posted a video series over three parts that while ostensibly about fixing his shredder, is in reality a three-part tutorial on how to create custom gears using FreeCAD. While the principles of a gear are readily apparent to most observers their intricacies hide significant complexity which he does a great job of explaining. How to measure the parameters of a given gear, explaining mysteries such as pitch angle or beta, he breaks everything down in easy to understand steps.

His tool of choice is FreeCAD, and while he explains that FreeCAD has the ability to make gears from scratch the tool employed in the videos is the Gear Workbench plugin. He shows how this software removes the complexity of creating a gear, and shows the process on his screen as he creates the custom shredder part.

Finally, the process of 3D printing the gear is explained. You might ask why not machine it, to which he responds that tooling for non-standard gear profiles is prohibitively expensive. We’ve placed all three videos below the break, and we think you might want to make yourself a cup of tea or something and work through them.

Thanks [Andy Pugh] for the tip.

16 thoughts on “Home Made Gears Save This Shredder

  1. “This is a problem particularly with plastic gears, which shed teeth faster than a child who has discovered the financial returns of the Tooth Fairy”
    That line made me laugh really really hard, brilliant choice of words!

  2. Any tips on making 3d printed gears at least as strong as the injection molded originals? My ABS printed gears could not withstand the forces required by a similar application… I will try stacked laser cut plexi, should be stronger.

    1. Stronger only if you put metal axle ton link your cut plexi, glue won’t be strong enough (well it could work but if you want equally as strong), you will need something that keep them well in place and glue is good for normal forces, sheering it’s not as good (iirc not even close)

        1. In this application the gears just wore out over time. My problem with machines that include bigger forces, like the shredder in the article, is teeth stripping. And in my case the ABS replacement stripped it’s teeth during the first day of use, while the original molded part lasted at least a couple of years!
          I really wonder how long the article’s printed gear will last.

    2. You could anneal your printed gears to improve strength. Low temperature in a water bath like a sous vide would be ideal.

      Parts will shrink slightly so you’ll have to play around with oversizing a bit.

      1. I would second this suggestion just because I used to machine nylon, both natural and nylotron 6 (black blue nylon, impregnated with molybdenum disulfide grease).

        I cut many thousands of large natural nylon gears in halves that pinned together, with teeth maybe 1/2 across, on 13″ diameter for chicken rendering assemblyline machinery.

        Nylon is very wear resistant. I think if you print with it, you’d get good wear resistant gears. PEEK would work well too, but I know from experience PEEK is hyper sensitive to heat distortion. I’d machine 0.005″ off a 12x24x0.250″ thk sheet, and it would warp into a potato chip almost 1/2″ in the middle.

        metal filled or even better- glass filled plastic would be very wear resistant. Machined those too- and they were all for parts needing high wear resistance.

        Hope this helps someone

        1. Nylon would probably be more available to most 3D-printerists :-) I haven’t used it myself, but i’ve heard PEEK is hell, and an expensive one too.

          With a 0.2mm nozzle i bet you’d be able to print even the smallest of gears, i’ve tried myself.

        2. I had a friend who fixed sewing machines, he once mentioned that on a Singer machine a nylon gear would often strip a brass gear that it meshed with.

          They also had a laminated fiber gear, I don’t recall the reliability of that one.

          1. Also a watchmaker. In watches and clocks- its almost always the steel pinions that wear out first- not the softer brass gears.

            The softer material acts as a lap on the harder material- micro particles get imbedded in the brass, and turn into an abrasive lap that eats into the steel gear eventually.

            This principal is often universally carried across systems, so it doesnt suprise me. Nylon is very hard and brittle, but still acts like a lap on steel im sure.

            Those fiber gears are usually micarta laminate, and they either last forever or seem to delaminate.

            Also liking this intro to FreeCAD, especially the cycloidal gear making. I really need to get away from Autodesk. Really impressed be FreeCAD lately.

  3. FDM printing almost always leaves tiny voids throughout a print, how about soaking the item in cyanoacylate infiltrant used for powder 3D printing? With some air pressure and/or vacuum to get it forced throughout the print, then removed and excess shaken off, it should be stronger once the stuff cures.

  4. Can’t wait for the day plastic gets replaced for good! If some other material other than plastic was used for making 3-D parts, I’d be more into this more. Not that my comment will mean much, but I think plastic use has outlived it’s purpose, especially when using metal with plastic is a failure that these makers of products enjoy failing at to profit in our failure to hold them responsible. But to make our own parts better & which will make our things last a whole lot longer is a good way of knowing if we can do this, we can make our own. Plastic has it part but very minimal. Then comes the time when a plastic piece will surely leave you high & dry, especially where high heat is expected weather inside & outside at the same Time is a malfunction ready to take place. Plastic, sensors, street lights you have too many of em in a spot & they just become a nuisance of problems that people let move in not considering the draw back & down time that they will play on us living a smooth & easy life!

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