1708 Bi-axle over Balsa

Discussion in 'Fiberglass and Composite Boat Building' started by mjkkemper, Jun 20, 2012.

  1. mjkkemper
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    mjkkemper Junior Member

    Looking for opinions if putting 1708 bi-axle is ok over endgrain balsa. Or should i put chop mat then the 1708? I want to keep the weight down so I was thinking of just putting 1708 over the balsa core instead of a chop mat.
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Without knowing what you are exactly doing.. yes, no and yes again.. :)
     
  3. mjkkemper
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    mjkkemper Junior Member

    It's a core for a hardtop in a neg mold so after I imbed the balsa core the next layer I was thinking of going to the 1708 biaxle. Before I would use a layer of chop mat to get good adhesion and incapsulate the balsa core. My question is bi axle a

    1. Ok
    2. Doesn't make a difference
    3. No don't do it it will delaminate


    chose for the first layer over balsa?
     
  4. TeddyDiver
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    TeddyDiver Gollywobbler

    Chop mat is only dead weight in a hard top IMHO, so 1. But you are not saying are you using poly or epoxy?
     
  5. mjkkemper
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    mjkkemper Junior Member

    Agreed on the dead weight thats why I wanted to avoid it.

    Poly resin
     
  6. AVMan
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    AVMan Junior Member

    1708 over Balsa

    The 1708 biaxial already has a roughly 3/4oz chop attached to it, so as long as you prep the balsa surface, apply the 1708 chop down, and consolidate the biaxial correctly you should have a good bond.

    Be sure to coat your balsa with resin first, to make sure all the end grains are saturated before you apply the 1708. If you don't, the resin in your chop layer may drain into the open grains.
     
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  7. mjkkemper
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    mjkkemper Junior Member

    Thanks! Makes sense I was worried about the balsa sucking up the resin and not getting a good bond.
     
  8. Saildude
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    Saildude Junior Member

    be extra careful with the saturated part - the end grain Balsa will suck up resin like crazy so keep an eye on things and add more resin to any area that is not shiny (i.e. the resin has went into the wood) - only takes a few minutes but the first resin will just disappear into the end grain and you will need to add more to the end grain almost as soon as you get the first bit down
     
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  9. tunnels

    tunnels Previous Member

    what do you think ?

    Resin coat the balsa as a sealer coat and let go off !! yes you need csm under and over 1708 the layer thats possibly already on the matt is a sprinkling so 450 under as a sandwich layer against the balsa and 300 on topto add to what possibly alread on your 1708 !

    The pictures i posted are a good example of 2 mats same weight but one is better made and flatter . Its why i get up close and personal with my job !!:D
    when a sales person shows me a sample and tells me its good i want to understand why its good !!
    Theres always a reason for using some products over others and in this case the stiched glass (local Chinese manufactured ) is far better than anything else i come across any where !! has a 450 on one side stitched and wets out really quickly and lays down and only needs a minimum of rolling . so easy and quick specially when doing a 90 foot hull ,cuts well and doesnt fall apart is another added advantage :)
     

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  10. Steve W
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    Steve W Senior Member

    Im not seeing any pictures of mat Tunnels, just roving, woven not stitched which would usually call for mat between the layers with poly. 1708 does in fact have a 3/4 oz mat stitched to it, i would do as Avman said but substitute vinylester in place of polyester, were trying to keep weight out of this thing.

    Steve.
     
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  11. tunnels

    tunnels Previous Member

    1708 ? doesnt mean much to me !

    Ok biaxle glass with csm ! what weight is the csm??
    The glass running in either direction you need to check if the are balanced and the same weight . 0/90 !! some have a heavyer glass running one way on the 0 degress and a lighter glass going in the other direction 90 degress across . so you have to work out which way you need the strength . .
    Always when covering a balsa core you need a sandwich layer between the glass and the core even if it was a foam core the same applies .
     

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  12. bntii
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    bntii Senior Member

    If working in epoxy:
    I would wet out with neat epoxy and then roll out a quick coat of goo thickened with colloidal silica. Lay up with straight 17 oz biax or even 12.
    The work will gel as you go and the rest of layup is done with laminating resin with perhaps a bit of CS mixed in.
    You definitely do not need additional csm under 1208 or 1708.
    Balsa is sort of heavy- do you need it or can you go with foam?

    How large of structure?
    How much support? Thickness of core? How much weight to be on carried on top?

    Just a hard dodger or a large hardtop with people standing on it as they strap down a tender with engine???


    1708 is 17 oz stitched biax with a 8 oz csm layer.
    If you want to keep the weight down- vac bag the whole deal.
     
  13. mjkkemper
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    mjkkemper Junior Member

    What type of foam core?
     
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  14. midnitmike
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    midnitmike Senior Member

    The critical thing here is making sure you have a sealed surface on your balsa core. You can do this by flooding the area with resin, or use resin thickened with cabosil or microballons to seal the surface. If you don't get a sealed core and it pulls resin from your single biaxle lay-up you can end up with a failed laminate. Adding one or more layers of CSM is a way to insure you have enough excess resin in your laminate schedule to allow for some minor loss of resin into the core.

    I've seen it done both ways and I'm partial to sealing the core with cabosil...then adding an extra layer of CSM prior to putting down the biaxle. If you ask me flooding the part with resin just adds weight, but it is faster and goes beyond just sealing the upper surface since it can penetrate down into the core filling voids that you can't see between it and the lower laminate.

    MM
     

  15. TeddyDiver
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    TeddyDiver Gollywobbler

    It boils down to question weather to use poly, make an unwanted layer of csm, use more resin and have heavier laminate.. or use epoxy, err.. less epoxy, no csm and no excess weight.. considering the amount materials no big difference in the price.
    Hard choice?
    BR Teddy
     
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