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OT? Composite construction for R/C aircraft, boats, etc.

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  • OT? Composite construction for R/C aircraft, boats, etc.

    I could use a CNC mill or router to do the same. Currently 3D printing molds for carbon fiber and fiberglass construction for R/C airplane components. I have a roll of Carbon Fiber cloth coming, and still have a big box that I haven't opened up from Aircraft Spruce(Burt Rutans moldless construction starter set) that has nichrome wire, micro balloons, fluffy cotton stuff, peel-ply, bidrectional and unidirectional fiberglass cloth, resins, etc.
    I was inspired by watching RamyRC channel on Youtube. He builds large airliner models and started to 3D print his molds that he hand lays fiberglass and carbon fiber into, without even using a vacuum bag.
    I've built a large enclosure out of foam board to trap the heat inside the printer to reduce warping and have a web cam that monitors the progress without opening the door. Starting off small, going to make a new vertical stab and rudder out of CF for one of my airplanes.
    The 3D printed molds require post processing of course. Spackling, sanding, wet sanding, maybe paint? Waxing of course as well, then a layer of PVA painted on.
    The heated chamber really seems to help things, get better prints even with PLA. I now have a need to get a MUCH larger 3D printer, the Creality CR10S Max is looking mighty good right now should this method work out well for me.

    Ultimate goal is to go full fiberglass and Carbon Fiber for all of my future home made r/c airplanes.
    Currently flying Electric Ducted Fans that go really fast. They are a blast. Want to build larger ones. Gas turbine ones even.
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    Right now the second half is printing, requiring no direct attention at all, just checking in to make sure it hasn't failed, at which point I would cancel the print.
    Click image for larger version

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    Last edited by RB211; 08-27-2020, 01:01 PM.

  • #2
    It's been a long time since I've done any model making. Back in the day of course it was balsa, paper, ambroid cement, dope, lay out frames, assemble with stringers. I very briefly got into carving foam, but since all we were getting then was polyester resin, a special foam was required so it wouldn't get eaten by the resin. We managed to build an F-86, but couldn't afford an engine for it. I built a few boats of my own design. I was quite excited about being able to put a scale model outboard motor on one of them.

    These days you can model just about anything using a computer. What I wanted was to be able to generate profiles by slicing up a computer model (which I was starting to create in 3D Studio Max) and then print them off as templates. You could build a far larger model that way than you could by 3D printing molds- unless you had a very large 3D printer. Another option I thought of was to have the computer trace out every profile of a wire frame model, then have a printer spit out a printed version of every wire with snap-together points at every intersection. By snapping together all of the mating points, the original shape would be physically recreated in a wire frame model- to which a covering would be applied. The 'wire' in this case would be the pla filament. Even a small 3D printer would be able to make the framework for a large model. It would probably not be good if you had large flat surfaces. Curved surfaces would hold up fairly well.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #3
      An inexpensive CNC router would be far faster for making molds like that I think. You could use wood, foam, or even aluminum like the fiberglass companies used to do for patterns that they laid up a master mold on. I would expect the part you are printing there to be done in maybe an hour on my little CNC machine.

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      • #4
        Originally posted by garyhlucas View Post
        An inexpensive CNC router would be far faster for making molds like that I think. You could use wood, foam, or even aluminum like the fiberglass companies used to do for patterns that they laid up a master mold on. I would expect the part you are printing there to be done in maybe an hour on my little CNC machine.
        Yes, a CNC router would be very nice to have for this stuff. In the mean time, I need to do this proof of concept, see if it is a viable way to make airplanes for my needs, and have a bigger workshop. If so...
        https://tormach.com/machines/routers...nc-router.html
        Last edited by RB211; 08-27-2020, 10:06 PM.

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        • #5
          so what does your "composite construction" look like? fiber glass and carbon fibre? what else? what resin?

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          • #6
            Originally posted by dian View Post
            so what does your "composite construction" look like? fiber glass and carbon fibre? what else? what resin?
            Same resin Burt Rutan uses on his Long EZ, etc. Have to look at the packing slip to tell you. Internal structure can be anything really, formers and ribs laser cut, or 3D printed, foam covered in CF for floor boards, what ever. I am post processing the 3d printed molds now for test pieces.

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            • #7
              if you got 3D printer, why not a 3D printed honeycomb structure?
              geez, you could do a whole wing as a single piece of honeycomb tip to tip, or, 2 pieces that join at the root.
              same for fuselage, print honeycomb bulkheads in-situ
              3D printing (additive manufacturing) has gone ballistic in their abilities

              You know the jet engine FCU? Fuel control Unit? all those teeny tiny orifice and passagways internal?
              that being 3D printed now, no more of all that drilling and aligning of fuel passageways.

              Machinist skills as we now know will go away. at some point lathes and mills will go away, the parts will just be 3D printed and over & done.

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              • #8
                Sounds like fun.

                Mind the temps inside the enclosure. You will need to move the power supply outside the box to keep it cool. I built the Lack v.2 enclosure and that moves the power supply. And the Einsy board is not really meant to be run in over 40C environments either according to Prusa.
                If you think you understand what is going on, you haven't been paying attention.

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                • #9
                  Originally posted by Ringo View Post
                  if you got 3D printer, why not a 3D printed honeycomb structure?
                  geez, you could do a whole wing as a single piece of honeycomb tip to tip, or, 2 pieces that join at the root.
                  same for fuselage, print honeycomb bulkheads in-situ
                  3D printing (additive manufacturing) has gone ballistic in their abilities

                  You know the jet engine FCU? Fuel control Unit? all those teeny tiny orifice and passagways internal?
                  that being 3D printed now, no more of all that drilling and aligning of fuel passageways.

                  Machinist skills as we now know will go away. at some point lathes and mills will go away, the parts will just be 3D printed and over & done.
                  Not now, not ever. The price of any object is most closely tied to volume produced and 3d printing will never be fast enough even if it can reach the accuracy a finish required.

                  However I think the whole idea of launching a rocket from earth and going directly to another planet is crazy. Park a solar powered 3D printer in orbit and print spaceships the size of ocean liners and power them with the same nuclear reactors that power subs today.

                  I suspect printing metals in space will be easier than on earth with no atmosphere and no gravity.

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                  • #10
                    3DLapPrint offers STL's for sale that are airplanes entirely printed out of PLA. Why do I not want to bother with that? PLA sucks for R/C airplanes, especially in Florida where they will melt like a pretzel if left in a car. PLA doesn't take much for it to reach its glass transition temp. Carbon Fiber is an amazing material and something that will last forever, especially in terms of an R/C airplane. Metal 3D printing is a really neat segment but outside the reach of most. It seems to be reserved only for parts that cannot be machined conventionally, which is pretty telling.

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                    • #11
                      Sounds like a good start to a fun project, assuming that your 3D printed molds are going to be used to vacuum bag your parts
                      you should take into account your molds imploding under the vacuum pressure if they are hollow underneath.
                      Adding a lattice or a egg crate pattern helps but depending on the thickness of the inside of the mold you might get print thru of the
                      underlying structure.

                      I've done a fair amount of vacuum bagging CF parts for theatrical productions over positive and negative molds, and back filling positive
                      molds with a rigid foam like Polytek Polyfoam R-5 ( 5lb density ) helps in making a lightweight strong pattern with no risk of print thru.
                      If you go that route, do the back filling in thin layers, a one shot pour will destroy your mold from the foam expansion.

                      Waxing and PVA in that order a definite must do.

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                      • #12
                        I have done a bunch of CFRP work, but I don't understand mixing fiberglass and CF. It is one or the other. The physical properties of CF blow fiberglass away, even E-glass. Consider using cores where they will work.

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                        • #13
                          Originally posted by polaraligned View Post
                          I have done a bunch of CFRP work, but I don't understand mixing fiberglass and CF. It is one or the other. The physical properties of CF blow fiberglass away, even E-glass. Consider using cores where they will work.
                          As far as R/C airplanes are concerned, you use Fiberglass where the receiver antenna's will be. CF does a great job of killing the RF reception of the 2.4ghz radios.

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                          • #14
                            Originally posted by jcfx View Post
                            Sounds like a good start to a fun project, assuming that your 3D printed molds are going to be used to vacuum bag your parts
                            you should take into account your molds imploding under the vacuum pressure if they are hollow underneath.
                            Adding a lattice or a egg crate pattern helps but depending on the thickness of the inside of the mold you might get print thru of the
                            underlying structure.

                            I've done a fair amount of vacuum bagging CF parts for theatrical productions over positive and negative molds, and back filling positive
                            molds with a rigid foam like Polytek Polyfoam R-5 ( 5lb density ) helps in making a lightweight strong pattern with no risk of print thru.
                            If you go that route, do the back filling in thin layers, a one shot pour will destroy your mold from the foam expansion.

                            Waxing and PVA in that order a definite must do.
                            RamyRC does not vacuum bag because it imploded his molds. Great idea on the expanding foam. I have a choice to make soon, spend 1000$ on a much larger 3D printer, or put that money towards a CNC router. I know the CNC router would be a much better investment. I have coworkers bugging me about doing work for them, I could make money tomorrow with a CNC router.
                            My wax came in today.
                            So to clarify, I fill the 3D printed forms with spackle, sand smooth, then paint them. Wet sand, some more paint, about 5 coats of wax and they are considered ready? PVA right before I do the layup work, and every time I use them. How often do I need to re-wax?

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                            • #15
                              Originally posted by RB211 View Post

                              RamyRC does not vacuum bag because it imploded his molds. Great idea on the expanding foam. I have a choice to make soon, spend 1000$ on a much larger 3D printer, or put that money towards a CNC router. I know the CNC router would be a much better investment. I have coworkers bugging me about doing work for them, I could make money tomorrow with a CNC router.
                              My wax came in today.
                              So to clarify, I fill the 3D printed forms with spackle, sand smooth, then paint them. Wet sand, some more paint, about 5 coats of wax and they are considered ready? PVA right before I do the layup work, and every time I use them. How often do I need to re-wax?
                              Get the CNC, it'll be faster and as you said a better investment, with the money made you get a bigger 3D printer.
                              I just noticed 7 hours to print that rudder ? You'll grow as old as Methusalah with a 3D printer

                              If you do use my expanding foam trick you must use a dense rigid foam, higher the density the better, at a much higher cost because the foam expands way less.
                              The insulation stuff you get at a hard ware store will fail, it's no better than packing peanuts. The Polytek R-5 foam I previously mentioned works well.

                              Wet sanding spackle will be like wet sanding drywall compound, you'll get mud and be back to square one . Dry sand if you must use spackle, that's my take on spackle.

                              I'm a bondo/ epoxy putty/ spot putty kinda guy when it comes to mold surfaces in vac bagging, spackle to me is also too porous like plaster ( i have vac bagged on plaster too )
                              unless you wax the bejeezuz out of spackle you'll find difficulty removing thin parts even with PVA.

                              Depending on the 3D print material you can use Nitro-Stan, or Acryl Green filler putties, Nitro-Stan is thinner and has a bit of a fragile nature in thick applications
                              easy to sand, Acryl Green is thicker but is stronger in thick ( about 1/32" max ) applications and a little bit tougher to sand. The aforementioned are solvent based
                              spot putties, auto body filler ( bondo ) works very well as does polyester spot putties, both are catalysed. The aforementioned should stick very well to ABS, dunno
                              about PLA, definitely not on polyethylene or nylon.

                              After all that said , you could just sand the inside of the mold to get rid of the stair stepping , prime with a good filling auto primer, wax ( 5 coats buffed between coats is good)
                              and then PVA sprayed at least 4 -5 coats straight no thinning if you can, I also mist the dried PVA with a suitable spray mold release,
                              you probably don't need to since wings and fuselages are pretty simple forms, the parts I vac bagged were pretty convoluted .




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