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best settings for snap fit pieces


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Posted · best settings for snap fit pieces

My design is flawed in that the tabs are hollow and pretty easy to break off. I know it is stronger to print in the other direction but I would still like to get this to work. I learned fusion 360 a little and took the .stl files to the library so I had no control of the slicer. But now I just got and printer and cura so hopefully I can change settings to make this strong enough. Any ideas on what to change? The broken tab is on the upper left of the pic.broke_tab.thumb.jpg.07b8f697bc6db3c44bd7e88b6bd8b036.jpg

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    Posted · best settings for snap fit pieces

    Did you print this in PLA or a higher temp material?  Because if it's a higher temp material there's a lot more you can do (you may have bad layer adhesion).


    1) Well in the "hook" end of the tab where it gets thicker now, you could make that thinner so the tab doesn't have to flex as much.

    2) You should make it thicker at the base where the most force is and have it thin gradually to just before the hook.  The idea is instead of having all of the flexure at the base, you want all of the tab to flex equally - equal strain everywhere.  The exact calculation I don't know but at least make it thicker at the base of the tab and thinner at the top.  You are doing two things here - making it thicker where it is most likely to break and making it thinner where it is less likely to break so it flexes more there.

    3) You can also make the tab wider at the base potentially and narrower at the tab.  This might not be practical or too much work in cad.

    4) Look at other materials.  For example "tough" pla  aka TPLA is designed exactly for this kind of thing.  Many plastics are slightly more flexible without being weaker.  The parameter you care about is best described by the "modulus" or the "young's modulus".  Google any material and "modulus" to get the mechanical characteristics.  All venders publish the modulus but pretty much all nylons are similar and all pla's are similar and so on.  Here's a chart showing some materials - modulus is the horizontal axis:



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    Posted · best settings for snap fit pieces



    Some of this gets into "try it and see" sort of engineering. For an item like a clip, doing up a very simple part and optimizing it may make sense. That way you don't burn through lots of time and filament each time you do another pass. Once you get the clip to do what it needs to, go back to the full sized part. 



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    Posted · best settings for snap fit pieces

    As gr5 already mentioned: don't use ordinary PLA: it may work a couple of times, but after a while it gets harder and tends to break. Even when printed in the "right direction". And it has too much permanent creep-deformation under continuous load. I use PET now for snap-fit lockings and keychains. It has enough flexibility to survive, and is still easy enough to print. Haven't tried tough-PLA yet, it's on my to-do list.


    And indeed, do small test pieces first, until you get them right.


    I would also recommend that you make keychains, carabiner hooks, cloth hangers, and similar stuff that you use every day. And in various materials. Have them sit in your pocket all day, let them lie around in your car in the summer and winter, etc... Then you learn how, why and when they fail, and you can use this knowledge in future designs.


    Carabiners: the green one is PET (from ICE), the cream ones are PLA/PHA (from colorFabb). They are about 6cm long and 2cm wide, outer dimensions. After a while, the PLA things will deform and crack like this.











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