3D Printing Improving Nose Cone Strength

Discussion in '3-D Printing and Related topics' started by PedroTheRocketNerd, Feb 4, 2020.

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  1. Feb 4, 2020 #1

    PedroTheRocketNerd

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    I have scratch built a 4" Nike Smoke with a 3D printed PETG nose cone. It has flown twice; the first time was a lawn dart, and the second was successful. However, on the successful flight, the nose cone broke in two upon landing. How could I strengthen the nose cone against this? (For reference, it was printed vertically, 0% infill, 1.6mm wall thickness.) I am already thinking that angling it in the slicer would be a good idea, so the layer lines are not oriented along the direction of force. Would that work? Is there more I should do?
     
  2. Feb 8, 2020 #2

    patelldp

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    Thicker walls for a cone that size. Try a fatter nozzle...0.8m mm nozzle with 4.8mm walls (3x inner, 3x outer walls). Print slow. It'll be heavy, but that will keep you from breaking the cone. If you elect to go thinner walls consider an internal structure.
     
  3. Feb 8, 2020 #3

    PedroTheRocketNerd

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    Thank you for the tips. I have not had problems with wall thickness on other nose cones with lower L/D ratios, but the Nike Smoke just has such a huge nose cone - and so skinny - that even 1.6mm walls are not enough. I have retired the Nike Smoke, because upon landing a fin broke and the body tube was damaged in the fin can area, but I will definitely use this advice if I am ever printing a nose cone of similar dimensions again.
     
  4. Feb 8, 2020 #4

    PedroTheRocketNerd

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    I think part of the problem is the layer lines. The breaks occurred primarily along the layer lines, which leads me to wonder if there are not ways of getting the layers to better resist delamination.
     
  5. Feb 9, 2020 #5

    Winston

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    I think liquid resin layer infusion via brushing or dipping the nose cone might help. On that, here's a guy who didn't use a resin intended for 3D printing, but used one intended for model casting:



    Personally, I've wondered if brushing on a cheap as possible resin intended for 3D printing would work:

    500ml for $17.90 shipped
    https://www.amazon.com/PHROZEN-UV-Curing-Shrinkage-Precision-Printing/dp/B083S654C7

    followed by hanging the nose cone inverted during a SLOW UV cure (to avoid as much heating as possible) using a 405nm LED strip placed at a slow-cure distance:

    https://www.amazon.com/s?k=405nm+led&ref=nb_sb_noss_2
     
  6. Feb 9, 2020 #6

    dr wogz

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    One thing a lot never think about is to split the part into 2, 3, or 4 pieces, and print them, then glue them if you split it in two, from tip to tail, the layers will then run along the axis of flight, not perpendicular to it.. Also, if you split into a few pieces, you can add features to add some stiffeners to the parts, like a wood rib or dowels or ..

    A few will also design the nosecone based on the profile, and revolve it around it's axis, then print it. And never think to look at the structure and add some reinforcement of some sort, be it incorporated ribs or bulkheads, added other materials, etc..

    of course, printing out the part, then wrapping it in cloth / fiberglass with a glue / resin as the binder, then sand to finish..
     
  7. Feb 9, 2020 #7

    lakeroadster

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    How about some Great Stuff spray foam... ?
     
  8. Feb 9, 2020 #8

    rharshberger

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    Use Sika Post Fix 2-part foam instead or another 2-part foam, Great Stuff is never recommended in rocketry for as long as I can remember due to the fact it requires air to cure and it wont cure fully in enclosed spaces. I included a link to the usage and testing I did with Sika Post Fix which is available from some home improvement stores like Lowes.

    https://www.rocketryforum.com/threads/sika-post-mix-expanding-foam.150303/
     
  9. Feb 9, 2020 #9

    Winston

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    Better and probably lighter results could be accomplished simply by using infill. Right now, he's just printing a shell. I'm not sure how he's generating the STL for the nose cones, but a wall thickness that would allow a 10% honeycomb infill between inner and outer shells should fix the splitting problem.
     
  10. Feb 9, 2020 #10

    lakeroadster

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    Says who? It's specifically used in enclosed spaces all of the time.
     
  11. Feb 10, 2020 #11

    rharshberger

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    Says many discussions here on TRF about spray foams. If in doubt PM Crazy Jim among others, and ask him for his opinions on Great Stuff and similar. My experience with it in nosecones and fin cans has been less than pleasing, and I am not the only one.
     
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  12. Feb 10, 2020 #12

    lakeroadster

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    OK, I understand. It's a personal preference and not "never recommended in rocketry" at all. I thought you were referring to some NAR specification, or something along those lines.

    Thanks for clarifying.
     
  13. Feb 10, 2020 #13

    PedroTheRocketNerd

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    I think resin coating might be useful for increasing strength between layers, as well as making finishing a lot easier (no layer lines to fill). Smooth-On makes a product called XTC-3D which is a 2-part resin for coating printed parts. However, I have no idea whether it would add strength or not. I also wonder if the UV-cure resin would actually add strength between the layers.
    This seems like a great idea with smaller nose cones. However, it would not be feasible with my Nike Smoke's nose cone, which is over 2 feet long. That would mean splitting it into 6-8 pieces, even more than the 4 I already had to split it into to print it vertically. I may try it, though, at some point in the future. And as far as glassing the cone, it would likely work, but I am not sure my building skills are up to that point yet. It seems like glassing a cone would be tricky, and I would like to get some experience with glassing tubes first.
    To generate the STL, I used OpenSCAD. I just generated it as a solid model, then used slicer settings to achieve the hollow cone with the 4 shells. However, it does seem like adding infill between an inner and outer wall would decrease the chance of layer delamination, simply because of the increased surface area between layers for better bonding.

    Thanks for all the ideas!
     
  14. Feb 10, 2020 #14

    Winston

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    The 2-part modeling resin he used in that video greatly improved part strength. That's why I suggested the cheaper UV cured 3D printing resin.
     
    Last edited: Feb 10, 2020
  15. Feb 18, 2020 #15

    Wallace

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    Just run a BT "spine" down the center and foam it. As a bonus, Ya get a free tracker bay. Just be aware that 2 part foam is pretty aggressively exothermic so an icewater bath would be your friend.
     
  16. Feb 21, 2020 #16

    PedroTheRocketNerd

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    I like the idea of the "spine." I have retired the Nike Smoke due to tube damage in the fin can area. However, in case I decide to attempt it again, or build other rockets with similarly high L/D nose cones, what is the density of expanding foam? I would like to keep the rocket light enough to fly on mid power motors, and I would not use the foam if it were prohibitively heavy.
     
  17. Feb 21, 2020 #17

    rharshberger

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    2 part foams come in multiple densities from something like 2 lb/cf to 16 lb/cf. PML or Giant Leap Rocketry has one thats variable density by adding drops of water, which may work with other brands but I have not tried it. The Sika Post Fix 2 part foam is about 3 lb/cf iirc, and its like $12 for enough to fill about 2 or so cubic feet iirc.
     
  18. Feb 21, 2020 #18

    Wallace

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    As Rich stated: It depends. There are a lot of variables you can use to get to your desired weight/strength ratio such as lightweight vs heavy wall body tubes, differing foam densities, intentional voids, tracker bay sleds/hold downs, etc. PML variable density foam is neat stuff (again as Rich alluded to, probably works with any foam since they are 2 part, moisture cured polyurethane foams) but can take some experimenting to get it "just right" since relative humidity at the time of pouring also also plays a part. It's also good practice to do multiple small pours vs one large one to avoid "crushing" the bubbles out of the lowermost section therefore losing the lighter weight aspect. If you play it just right you can end up with a one off custom part that's the same weight or even lighter than an off the shelf piece. I personally find it to make a sweet two'fer when your rocket requires
    nose weight in the first place.
     
  19. Feb 21, 2020 #19

    Leo

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    I'd check for layer adhesion. What temperature are you using on the hotend side for PETG? What does the manufacturer of the filament suggest?
     
  20. Feb 21, 2020 #20

    cwbullet

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    I had a ballistic flight with a 38mm cone PEtg and CF without reinforcement. The cone survived and the rockets did not.
     
  21. Feb 21, 2020 #21

    Wallace

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    Petg is tough stuff. Just enough "give" to keep it in one piece. Abs has toughness also but can be a pain to work with.
     
  22. Feb 21, 2020 #22

    cwbullet

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    No only that, ABS on the prusa can stick too well.
     

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