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  1. #1
    Stoked! BraytonL's Avatar
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    Question Longboard Mold - W Concave Concept HELP

    Please tell me if there is something I'm doing wrong here, whether it's where I'm posting or the format in which I'm doing it. First post, first day with an account, cut me some slack but give it to me as well.

    I'm building my first board, 7 ply - 1/16" maple veneer, using the vacuum press method. I decided I wanted to have a W concave, and since I have access to a CNC at the local makerspace I figured I'd just CAD something up and mill it out of dense foam insulation (polystyrene). Here's what I have put together so far, please take a look and tell me what you think. I'm unsure whether the curves are too intense, I know the board will naturally snap back a bit when coming out of the press so I made them pretty steep. Thanks for any help in advance, you can view the file in complete 3D online.

    LINK: https://gallery.autodesk.com/fusion3...?popupSNS=true

    *The holes in the dip are so that when the air is being removed it 'pulls' the board into it, getting a W shape.

    *The name is Bob Schneider I think because I set it up an Autodesk account back when I was paranoid about my name being on the internet... I promise it is my own design... not that it is much to be proud of.


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  3. #2
    Addicted Cruiser MrBoard500's Avatar
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    Default Re: Longboard Mold - W Concave Concept HELP

    Looks pretty good. The W might be a bit harsh though. The holes that you put in to add more pressure will also pull the veneer deeper into the W of the mold. Concave is all preference but if I was making it I wouldn't like it much.

    Maybe go to a local board shop and stand on one to get a feel for the concave. The first board I made had so much concave I couldn't stand on the board with out having both feet at a 70' angle where most want them are 45'

    Just some advice


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  4. #3
    Addicted Cruiser bandaro's Avatar
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    Default Re: Longboard Mold - W Concave Concept HELP

    Nah way too steep and harsh a mould.

    I don't want to sounds mean, but I would start over, you haven't made it with experience in the method of manufacture in mind. So given you are using maple veneer, it is absolutely critical you have a tight press (contact) between the mould material, all your veneers, and the bag. If you have a hollow like that in the centre, the veneers will not be getting "clamped" together and your glue lines will not hold up.

    You won't need the holes either, the bag with a breather cloth will sort it out nicely (contrary to popular belief, the bags don't "pull" the veneers down. The air is pulled out of the bag so the atmosphere pressure squashes the board, giving a vacuum bag that even pressure they are known for. You will only need holes if you are pressing a non breathable material that is sealed perfectly to the mould). The way I model my boards is create a surface exactly how I want the board to be/10-15% steeper curves, then offset it down the thickness of my materials to give me the bottom surface of the board. CNC this with a 12mm bit at 95% fill, chuck the veneers on top and crank a vacuum.

    Just a random image from google, but a good vacuum mould would look something like this:

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    Other points of note, veneers tend to not do 3D curves too well, try to keep them to a single axis where possible. I make sure my moulds will thicken in both directions at least 50mm to reduce splitting in the veneer. The more glue lines (ie. veneer vs ply) the less "spring back" you will have. So 7 ply veneers have 6 glue lines, enough to make the spring back minimal. Ply of the same resulting thickness could spring back 50% or more as it only has 2 glue lines. I'm sure Ted from roar rockit has a bunch of tutes on mould making for his thin air press kits. I also don't bother with foam anymore, I find MDF to be cheaper to buy, as fast to machine and capable of multiple boards - but it's heavier and messier.
    Last edited by bandaro; 08-07-2016 at 01:45 AM.

  5. #4
    Stoked! BraytonL's Avatar
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    Default Re: Longboard Mold - W Concave Concept HELP

    Quote Originally Posted by bandaro View Post
    Nah way too steep and harsh a mould.
    I don't want to sounds mean, but I would start over, you haven't made it with experience in the method of manufacture in mind. So given you are using maple veneer, it is absolutely critical you have a tight press (contact) between the mould material, all your veneers, and the bag. If you have a hollow like that in the centre, the veneers will not be getting "clamped" together and your glue lines will not hold up. .
    Thanks, I have actually gone through over 6 variations of the mold now, so starting over is not a big deal. My most recent is posted here: https://gallery.autodesk.com/fusion3...?popupSNS=true
    (same project, just added the second model).

    But from your advice I obviously need to restructure it once again, which is totally not a problem, starting fresh always helps clean things up anyway. Any advice on the side concave? I used a design similar to what Roarockit does where instead of just a straight line concave, its more of a curve that tapers at the ends of the board. The inner part of the 'w' will definetely need to be reworked. Trying to finish this today so I can go CNC it at the makerspsace.

    Once again thanks for all your help, very detailed and well explained.

  6. #5
    We build your board Concrete Kahuna AM Wood Skateboard Co's Avatar
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    Default Re: Longboard Mold - W Concave Concept HELP

    too aggressive. by.... a lot lot lot.

    The foam should be in contact with the wood everywhere, no "floating" sections.
    for perspective, 1/2" of w to base of concave is pretty high.

  7. #6
    Addicted Cruiser bandaro's Avatar
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    Default Re: Longboard Mold - W Concave Concept HELP

    Again, keep in mind the materials when you are designing the mould.

    The veneer is thick, stiff, and not very flexible. It needs to be able to be pressed onto every single part of the mould surface, very snuggly, without splitting to get a glue join. When you do a curve, imagine it cut out on the mould, and think "will a sheet of A4 paper conform to this surface without creasing or tearing in any place? If not, then there is no way a veneer will. Do you have the veneer already? Try bending it, see how it goes.

    This is one of my test moulds from a few years ago. The rectangle on the end was trimmed off prior to use, and I still had a small amount of splitting on this mould. Remember you cut the shape after pressing, so model that whole big rectangle the veneers come in. I think the deepest point in the w concave was about 12mm from top-bottom, with the bowl at the front about 18mm deep in the model, and it's about as steep as you would go. The pressed board will be an almost identical copy of the mould.

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  8. #7
    Fresh Fish TechTeacher's Avatar
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    Default Re: Longboard Mold - W Concave Concept HELP

    If you need a mold to use, feel free to use mine in my signature.
    For skaters, by skaters.

    Check out my longboard CAD files below. Included is STL files for molds, ShopBot toolpaths for the molds and deck profiles. instructions on how to make molds and pictures of the process along the way.

    Files
    https://grabcad.com/library/longboard-mold-1

    How we do our layup, press and add fiberglass:
    https://www.youtube.com/watch?v=gNz-CEl3B2w

    How we machine them:
    https://www.youtube.com/watch?v=nf8Oc9aaBzU


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