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  1. #1

    Need design advice for interlocking parts

    New to the board and to 3D printing, and looking for advice on finalizing the design, and choosing the material and printing technology. I have designed a pair of interlocking plugs in Sketchup to lock the ends of two boards at 90 degrees. See photo - shows two separate plugs, but I changed the design to make the two into a single plug, as shown in the Sketchup model. The two boards are extrusions made from Resysta, a manufactured material used for, amongst other things, siding on a building. The two interlocking parts "plug" into the ends of the extruded boards and lock them together. See second photo. I need 20 sets of these plugs. The installation is outdoors in Chicago. I can create .stl files from Sketchup and upload to a 3D printing site, but I'm not sure if I need to allow space around the "tenons" for clearance? Will the parts that fit into the other parts need to be a smidgen smaller? I do want a "friction-fit" not a loose fit.I thought of specifying TPU for flexibility, but the colors are very limited - the boards are brown, so I want the plugs to be a similar color. Would a different material be better?Any advice would be appreciated. Happy to share the Sketchup file, too if that would help.Cheers,Allan
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    Last edited by akirson; 10-25-2022 at 03:39 PM.

  2. #2
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    It's typical to provide for as much as 0.2 mm difference between joining parts, to ensure that once printed, there will be sufficient clearance for assembly. For a tighter fit, change the clearance to 0.15, although going as far as 0.10 is risky. If you are using an online printing service, they may specify the acceptable clearance in the fine print.

    SketchUp is known for creating non-3D-printable models. Consider to upload the STL file to an STL file checker to see if you were able to avoid the usual pitfalls.

    How much flexibility do you require? PETG has a decent amount, and nylon is astonishingly strong and flexible.

  3. #3
    Thanks, much, Fred.
    Quote Originally Posted by fred_dot_u View Post
    How much flexibility do you require? PETG has a decent amount, and nylon is astonishingly strong and flexible.
    Just enough compression to push the tenons into the wood extrusions - I don't want to split the wood by forcing them in. Given that the tolerances of the wood extrusions are probably not that tight, maybe I should allow a bit more than 0.2mm?

  4. #4
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    Another way to approach the joining as described is to design in what is known as a compliant structure. Depending on the overall structure, a set of fins that will bend slightly backwards as you push in the part will also secure the joint without breaking.

    One suggestion I have is to consider a re-make of the part via the rather simple but appropriate program known as Tinkercad. It's on a par with SketchUp, perhaps a bit easier to learn. Well, no, quite a bit easier to learn. The results would be nearly certain to be printable as well. An additional benefit is that you can turn on object sharing to make a design transfer all that much easier.

    I'm more of a fan of OpenSCAD, but if you aren't comfortable with writing code, it's not going to make things easier.

  5. #5
    I have an AutoCad login, so TinkerCAD is available to me. I just imported the .stl files from a Sketchup export. Worked fine. The idea of fins is a good one - how thick should they be so that the material will bend?

  6. #6
    Staff Engineer
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    There are other, more easily implemented options in the compliant structure world than fins, and more important, easier to print!

    Will the tenons be glued in place?

  7. #7
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    Also, I've been checking on appropriate filament types and find that there are not many options in the high-strength world. Another missing puzzle piece: what dimensions apply to this part?

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