Just a quick hobby + learning project. If people are interested I am happy to post more pics. PLA exterior + TPU seals + Nylon (COPA) bushings.

Everything is 3d printed except the hardware & motor. The hose adapters have 1/4 NPT ends on them. NPT has a tapered thread so I found that I could screw them in partway by hand then heat them up slightly with a soldering iron to soften the PLA then screw them in the rest of the way. Makes a nice watertight seal despite the roughness of the 3d printed threads. If they start leaking I can unscrew them (leaving behind threads perfectly molded to the fittings) then add some pip seal tape and put them back in.

What do you guys think?

EDIT: here’s a photo of the parts separate exploded_view

and a video: https://imgur.com/a/cd8co68

  • @j4k3MEnglish
    6•1 year ago

    I’m very interested in seeing more details and what you learned and came up with. The bushings and seals are of particular interest to me.

    1. I’m curious what you came up with as far as a TPU seal and how you retain it against mechanical forces.
    2. How good are your bushing tolerances with wear and what do you think the limitations may be for the material?
    3. I assume “watertight” means you’re pumping water? What are you doing to achieve an overall watertight print in the first place?
    • @pianoplantOPEnglish
      4•1 year ago

      Hey, thanks for your interest! I edited the post to add an ‘exploded’ view of the parts. This is prototype #2 and still has some significant issues that I’m working on (and would love community input on!)

      My strategy for a watertight print is as follows:

      • lots of perimeters and solid layers top/bottom on the individual parts
      • sand mating surfaces smooth and add TPU grommet/seal
      • apply significant pressure to compress the TPU to form a seal

      This has actually worked extremely well. The pump has leaks but none of them are from the 3d prints or mating surfaces. What I’m struggling with is preventing water from going out the shaft tunnel. This is a major issue because I’m currently using a chrome-steel bearing at the top for shaft concentricity, which will rust out almost instantly. I made the challenge harder for myself by using a hexagonal drive shaft so I can’t rely on tight tolerances there to keep out the water. I need to sort out a strategy for packing / sealing and/or switch drive shafts + use some kind of off-the-shelf option.

      I’ve also been looking into an alternate bearing solution e.g. ceramic. If I can find a good sealed bearing that won’t rust I might be able to just use a tight TPU seal between hex shaft and bearing ID to give it a watertight seal.

      The original design had several chrome steel bearings in it (newbie mistake) which I had to replace at the last minute with the nylon bushings. I’m working on a better solution.

      edit: see video I just added in the post as well

      • Flaky_Fish69
        3•1 year ago

        Are you printing gaskets in tpu or just laying filament and compressing that?

        I usually go to a trick I picked up someplace off the Internet using silicone caulk squeezed into an appropriate diameter of fish tank airline tubing. (Or for much larger seals, flexible pc liquid cooling tubes.)

        The trick is using an air compressor to blow it out of the tubing. (You can also make hollow seals by blowing the tube before the silicone is set.) then, just glue the ends with a dab of leftover caulk.

      • @j4k3MEnglish
        2•1 year ago

        Thanks for sharing. My next TPU gasket seal iteration was likely a full flat gasket after fussing with more of a printed o-ring like bead with a flat flange and channels built into the mating parts.

        As far as shaft seals, you’re in the “thar be dragons” region as far as I am concerned. Good luck!

        • @pianoplantOPEnglish
          3•1 year ago

          Haha thank you! Yeah flat gasket is simpler & has worked so much better than past attempts at o rings and such. Definitely the way to go in my opinion. Just keep in mind when the grommet is compressed it grows horizontally slightly so you may need to inset the perimeter slightly. (You can see I had to do that with the interior section)

    • @pianoplantOPEnglish
      4•1 year ago

      I’m researching adding a packing box to the design and switching to a round shaft. I think that’ll work better.