Fiberglassing

Discussion in 'Scratchbuild Talk' started by Kos-Mos, Jan 1, 2010.

  1. Kos-Mos

    Kos-Mos Rookie

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    Hi there!

    I have a project that requires something stronger, yet smaller in space than ABS or Styrene plastic I have been using to build the proto.

    I have ordered some 3/4oz fiberglass cloth and some resin kit.

    I need to build some negative mold before making the fiberglassing, because internal dimensions are more lenient than externals.

    I want to know if it would be possible to make a fiberglass negative and then apply some coating to prevent the final work from sticking to the mold. Since it will be resin/resin surface, I fear that some regular de-molding wax won't be enough.

    Also, I have never done fiberglass before, but did my research before jumping into it.
     
  2. MoTheG

    MoTheG Airman

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    That is common practice, no problem, just let the mold set befor you glue the positive to it. ;)
     
  3. Kos-Mos

    Kos-Mos Rookie

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    Thanks!

    I will try this in a few weeks...

    I am trying to find some carbon fiber cloth, any clue as to where to find some at a decent price?

    So far, the local auto custom shop wants to sell some to me at about 30$/sq.yard for 1oz. material... I don't know if it is normal price, but since I get the fiberglass equivalent for 5$/sq.yard....
     
  4. Crash-man

    Crash-man Rookie

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    Hey there!

    I have done TONS of fiberglass work over the years. My Pattern planes' fuselages were FG to cut down on weight.

    When you create your plug (positive), you want it to be as smooth as possible. The smoother it is, the smoother your mold (negative) will be. One of the tricks I used to do when preparing a new plug was to sand the part with the finest sandpaper I could get my hands on (600 grit, usually). If I had any pits or scratches, I would use spot-putty (like in the automotive paint industry) to fill the voids and then sand some more. When I had everything as smooth as I could get it, then I painted the plug with regular old rattle-can primer, and then sanded everything again.

    Believe it or not, if you have sanded that primer surface well, it will almost shine!

    Now here's the trick: after you've cleaned the plug thoroughly (tack cloth), apply a liberal dose of Carnuba Wax and polish the primered plug to a lusterous shine.

    All of this work ensures two things - 1. the mold will easily release from the plug, and 2. the mold will be incredibly smooth, which will facilitate easy removal of the finished part from said mold down the line.

    Trust me - all of this work is worth the effort in the end. :D

    Additionally, I highly recommend using the LIGHTEST glass cloth you can get your hands on for the first layer down for molds and finished product (and last layer down for plugs). For me, I used 0.6 oz cloth, but I've heard of lighter materials.

    Also, you cannot go wrong with West Systems epoxy systems. This stuff flows better than any other type of epoxy or resin that I've ever used, as well as providing a nice long pot-life.

    I hope this has been enlightening. Goodness knows that I've made probably every mistake that can be made while trying to learn to do this stuff! LOL
     
  5. Kos-Mos

    Kos-Mos Rookie

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    Thanks a lot!

    But since it is not for a RC project, I need the surface of the finished parts to be some what flat, and textured at some places....

    I will have to make at least 5 parts in total... and most of them will require a two pieces mold or more...

    Got some work to do! In the end, it will cost me more to make the molds than to make the actual parts. hehehe
     
  6. MoTheG

    MoTheG Airman

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    youtube and elsewhere

    there are many video- and photo- guides on the topic available online.
    go here to see a pro at work, he keeps sanding and priming a long time, but still had a minor problem getting it apart in the end, but the thing is huge so that was to be expected to stick at leased somewhere.

    edit:
    If you can not get inexpensive, small amounts of GF or CF or for learning/testing use some other fabric.
    I used cotton pillowsheet/bedspread ones, and it worked sufficiently. The fabric has to be tightly woven and should not strech (unlike a T-shirt).
     
  7. teflondon

    teflondon Rookie

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    if you wan't cheap carbon fiber go to a place that uses carbon fiber on an industrial scale and ask if they have any scraps that they trow away and if you can have them
    i know a company that makes parts for airbus and they gave me an entire box of theire scrap pieces most pieces are bigger than A3 paper and for kevlar i go to a company that makes bullet proof vest
    most company's are very polite and are happy to give away their junk
     
  8. Argonath

    Argonath Top Gun

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    Try visiting places that sell Fiberglass top campers / trailers. They usually have fiberglass supplies to repair the tops (We had one for years until it got crushed flat by the ice storm back in '98).

    Also, I used to get that stuff from Canadian tire years ago as well but that might not be something they stock anymore either...
     
  9. KCWolf

    KCWolf Rookie

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    Fiber Glass Alternative

    For those who can't or don't work with FG I propose the next best thing. Polyurathane and pantyhose. believe it or not this actually works. I inherited a trainer kit that had spent many years in a basement and was pretty banged up. The body was made out of cheap styrofoam that showed every bump, ding and crack. Here is the process:


    1. Stretch the leg of the hose over the model piece you are working on
    2. Once it is evenly stretched over the piece, lightly coat the piece with the polyurethane.
    3. After the first coat has dried apply the next coat, allow to dry and repeat until coat 5.
    4. At coat 5 give the piece a sanding to even out the surface, make sure that you work you way from a rough grit (120) to a fine grit (300)
    5. Apply coats of polyurethane with a light sanding in between until you have a smooth surface to paint.
    I have done this on one model and it made a great coating, adding about 3.5 oz to the total weight of the plane which was overcome with a motor/prop combo that produced more than enough thrust. A couple of key points:

    • the lighter the pantyhose, the less weight when done.
    • use the water base polyurethane (it cleans up more easily)
    • do not do this in direct sunlight, the wet polyurethane acts like a magnifying lens and will deform your foam body.
     
  10. KCWolf

    KCWolf Rookie

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    Fiber Glass Alternative Part Duex

    So just an update on this. Second plane coated and complete, almost a Ultracote like coating once painted. Third plane was another learnign experience. The body was longer than standard leg length so I sleeved it from both ends. I also decides to cut the toe area of a third hose leg and use it as a large tube mesh over the midsection in hopes of improving structural strength.

    When using multiple pieces of pseudo mesh (pantyhose), work each piece to it's final finish before adding another layer. placing multiple layers on each other before finishing the lower layer causes a spongy texture and makes it extremely difficult to sand and obtain a reliable finish.

    After using my dremel to grind the parts back to the styrofoam I began to follow the above advice. While the results I achieved were still not what I hoped, I blame it on the aftermath of the grinding process and the frustration level I had when I started re-coating thee body. The wings come out pretty well after I gave it a couple of days before starting on it.

    I'll try and post some pics when I can of the finished paint job and some of a pre-painted body.
     

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