Multiple Carbon Fibre Layers - how thick?

Discussion in 'Boatbuilding' started by HydroNick, Feb 10, 2014.

  1. HydroNick
    Joined: Apr 2010
    Posts: 87
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    Location: British Columbia

    HydroNick Nick S

    I am in the process of repairing and modifying the rudder cassette on a Farrier F-25c. I want to add an additional thickness of 6.35 mm to one section of the cassette which I will do with layers of carbon fibre and resin infusion. For various reasons I am not interested in adding CF plate and because some of the thickness will be machined out, I can't bulk the addition up with core.

    The carbon fibre I am using is 6.5oz warp unidirectional CF , specified as being 0.18 mm thick which indicates 35 layers will be required to add a 6.35 mm thickness (it is only a small area). The alternating layers will be at 90 deg.

    The CF specs are http://www.fiberglasssupply.com/Pro...ents/Carbon_and_Kevlar/carbon_and_kevlar.html it is C72-4109

    I have cut the 35 layers of CF but even when I pinch them down it looks like their total thickness will be a lot more than the 6.35 mm.

    Do I trust to the 0.18 mm/layer and the compaction ability of resin infusion or is there some other rule of thumb I should be using to calculate the end thickness?
     
    Last edited: Feb 10, 2014
  2. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I wouldn't trust it unless it says that the thickness is "X mm ,laminated".
    You could use a small amount of carbon and make a test...
     
  3. Baltic Bandit

    Baltic Bandit Previous Member

    What does you trusting it have anything to do with it?

    a) normally these specs assume that you are going to vaccum and infuse.
    b) when you do vacuum and infuse you will have a different thickness than just holding them together "pinching them down"

    Your best bet Nick is to do a test swatch , but if you are going to be milling it out anyway, why do you need it to be that precise?
     
  4. HydroNick
    Joined: Apr 2010
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    Location: British Columbia

    HydroNick Nick S

    Thanks to both of you...and yes, my precision is a bit over the top. I should have said "about 1/4 of an inch" Still, I don't really want to end up with way too much remaining thickness; though, that could also be ground down.
     
  5. HydroNick
    Joined: Apr 2010
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    Location: British Columbia

    HydroNick Nick S

  6. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ====================
    Just in case you haven't done it before: grinding carbon/epoxy is very, very nasty-worse itch than fiberglass and,of course, the dust is conductive so dust balls blowing around and into an electric socket or tool can be very dangerous. Good Luck!
     

  7. HydroNick
    Joined: Apr 2010
    Posts: 87
    Likes: 3, Points: 8, Legacy Rep: 38
    Location: British Columbia

    HydroNick Nick S

    Thanks Doug: I do know that CF particles were used in Kosovo to kill electricity supply...but had not thought of the other. Thanks. I had being doing some grinding and taking the necessary precautions. I am assuming that a machine shop will cut the slot for me.
     
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