Vacuum infusing wood that has been CNC'd to fit a mold

Discussion in 'Fiberglass and Composite Boat Building' started by Dejay, Mar 30, 2018.

  1. gonzo
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    gonzo Senior Member

    upload_2018-4-1_12-26-4.png
     
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  2. fallguy
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    fallguy Senior Member

    Truly a simple and cheap method to torture ply, curious the ply thickness of the drawing, and I’d still like to know if anyone has cat plans using s&g. I haven’t seen any.
     
  3. gonzo
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    gonzo Senior Member

    The Gougeon brothers used thin plywood 1/4" simply to generate a shape, then glassed inside and out.
     
  4. Dejay
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    Dejay Senior Newbie

    Well for me using plywood is about cost. From the prices I've roughly calculated 9mm plywood with 300g glass on both sides would be 44% of the price and 31% more weight than 10mm foam core with 1500g fiberglass on both sides. I don't know if that are good numbers and a fair comparison? Afaik the CM article also suggests using cheaper non marine grade plywood which could greatly reduce costs.

    And yeah I'm in the weeds haha. So much to read and learn. All your replies are very appreciated, thanks. I'm just trying to find a way use a CNC and cheaper materials to reduce costs.

    @gonzo
    That looks very interesting. Where is that from? A book or plans? Just standard stitch and glue?
    EDIT: Oh right I still have to read the Gougeon brothers book. It's from there?
    Looking at the bottom seam, I figure that is a butt joint stitched and glued flat together so it spreads hulls apart?

    I'm still wondering if there isn't a method for torturing plywood by pushing it into a mold and constraining it's edges with a top flange (or mold station / bulkheads). I can't think of a good real world example, but imagine snapping a sheet of plywood into a cylinder cut in half with flanges. Once it's in there it would be totally fixed in place.
    It seems it would be less work to torture and snap plywood into something than nailing it around something. Maybe use dowels to keep scarf joints together.

    Hmm... I guess that is basically the KSS method. Except you're not torturing the fiberglass laminate into shape but applying it over the curved shape.
     
  5. fallguy
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    fallguy Senior Member

    You are off on the cost estimates. Ply is more like 30% cost of foam...a bit more for okume. It might be less vs the method I am using. I am wasting a lot of epoxy wet bagging, peelply two sides, bleeder (reusable, but I bought enough to throw away), diffusion, gum tapes, vac bags (I get 2-3 parts outta 40’), masking tapes, fabric cutoffs even. The waste rate for my process is dismally embarassing. For a ply monocoque; way, way less waste. I spent 21k on core and epoxy alone for 32’. Figure 32k for simplicity and I’ll be at 1,000 a foot before painting or fitting anything; even windows; discounting labor I hired to help. Mine is an argument for infusion.

    Not meant to rip on my method, but point out the difference in cost. I will like the boat I build.
     
  6. Dejay
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    Dejay Senior Newbie

    I like the boat you're building already ;)
     
  7. rwatson
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    rwatson Senior Member

    Hi Dejay

    Its good to hear about new ideas. It kept my brain busy for years.

    To be honest, I think the best way has been discovered, and discussed a while back.
    I'm going to link to a video posted by Mark Bowditch, a guy who made some fascinating videos a few years ago, and has reproduced them here.

    Its a form of strip planking, and is what got mentioned a few posts ago - dry strip planking.

    Essentially, you staple all the strips to a male mould with a small 2-3 mm gap, and then you squeeze thickened epoxy into the gaps, and glass either side.

    It does away with that horrible option of having to glue and fit at the same time. The video gives a very basic view of the process towards the end, you will have to pause from time to time.

    The only advantage of strip planking is the ability to make really tricky hull shapes.

    If you are going to just live on a boat, hard chine plywood is the way to go. If you need better shapes, then this method of strip planking seems to be the ultimate method.

     
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  8. gonzo
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    gonzo Senior Member

    I think that a combination of plywood and strip planking is the fastest way to build, particularly narrow hulls. You can make large more less flat areas in plywood, like the upper part of the sides and the central part of the bottom. The rounded chines are strip planked.
     
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  9. Dejay
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    Dejay Senior Newbie

    Thanks, that video explains it very well and looks much less time consuming.

    I don't think I need any fancy hull shapes, what I want to optimize is fuel efficiency (solar power if possible), living space and build time. I think that means displacement hull and a cylindrical wet keel?
     
  10. gonzo
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    gonzo Senior Member

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  11. Dejay
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    Dejay Senior Newbie

    Awesome, thanks, that is very interesting. Oh and it's actually public domain and available on Gutenberg!
    Apparently they peel the wood like for plywood. They also cut "fingers" in the sheets like the KSS method to produce compound shapes. Nothing new under the sun :D

    I was looking into what local woods would even be available here in Germany for cheap that are suitable for boat building. Didn't know birch would work. I've read that larch is suitable as well. I guess wood selection is a whole other science.
     
  12. Rumars
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    Rumars Senior Member

    Dejay, everything that needs a mold is at least the same amount of sanding and fairing. The plug to make the mold needs to be sanded to perfection before the mold is made. Sometimes the mold itself may need some aditional polishing. It only makes sense for production settings where you make more than one hull. High production boatyards use any technique that is economically viable. The thing is that even if the technology is here to have a boat build entierly by robots, boat building is just a to low numbers affair to justify the needed tooling costs. If you build 1000 units of one boat you are considered a high volume builder and any sailor will recognize your name. In the automobile world with the same numbers you would be a speciality builder known only to a few people. Basicly in boatbuilding it often makes more sense to hire people than to use robots for some jobs. Plugs are cut on huge 5 and 7 axis CNC's but hand sanded. This job is often outsourced since it's cheaper than buying the machine. You could automate the core and fiberglass laying, but its not cost effective. Infusion on the other hand is cost effective even with the consumables, since it produces a consistent quality product, and allows fewer people to do the same job. Any tehnique you use has to pass the cost/benefits matrix. Materials cost is the last thing to be considered, and often resale value is more prominent. Meaning that if balsa core is cheaper than foam core you still use foam because customers think badly of balsa. If the customer wants a carbon fiber toilet bowl, you better make one if you want him to buy the boat.

    Now back to your hexagon ideea: even if you double the layers and offset them it still will not be an active core. The fibers are just to short to do that. You have just doubled the work and used more epoxy to achieve the same thing end grain balsa or foam do, with significantly more weight. The fiberglass skins need to be the same thickness as for the equivalent thickness foam core.

    CNC machining is used where it makes sense. Meaning anything out of sheet goods, from jigs, interiours and up to the hull plating. For amateurs it's cheaper to outsource this, since you don't pay 5000 for mediocre machine but pay 1000 for cutting on a really expensive and accurate machine.

    When torturing ply one does not use a mold because every sheet of ply bends differently and the hulls can not be made exactly the same. If you want consistency you dont use ply but laminate veneer into a custom piece of ply in the shape of the hull. It's called cold molding and is done over a male plug, as opposed to hot molding wich used to be done in female molds.

    In Germany you can buy any commercially available wood species from earth, but if you want native species only four are suitable. Those are silver fir (Tanne), norway spruce (Fichte), scots pine (Kiefer) and larch (Lärche). Pine and larch are really to heavy for strip planking a light multihull, so fir and spruce are your choices. The other light wood that is affordable, light and not rot resistant is Abachi, a tropical hardwood. European grown paulownia is available only in theory.
     
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  13. Dejay
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    Dejay Senior Newbie

    Thanks Rumars, yeah I see the idea of using hexagons doesn't have good advantages. It's worse than wasting the middle veneer in plywood if you're cutting it into strips for cold molding.

    But wait, I have another one! ;)
    I've been reading up on the various methods for wood boat building (strip planking, ashcroft, cold molding, planking, tortured plywood) and I've been wondering if a female mold and CNC could maybe help there.
    What if you used a female mold just out of mold stations and stringers and a top flange.
    Then have the CNC cut all the veneers for cold molding to the exact right dimensions so you could then just bend and "snap" them in position in the mold? This could work for strip planking, ashcroft or strip planking as long as the puzzle pieces fit exactly and you start at the right corner to find purchase and constrain the elements into the mold from the edges.
    I hope I'm explaining that well enough. Imagine taking off all the already fitted pieces from a male mold and putting them into a female mold instead.
    Theoretically you actually could automate the planking using some kind of robot gripper arm. But like you say, lots of investment.
    And since you don't drive nails into the mold you could put a vacuum bag behind it and infuse the shell in one go instead of laminating each individual veneer.

    My guess is that it won't really save time either. You save some time not having to nail and glue and fit each individual piece, but instead you have to push every single piece of wood through your CNC which creates a hassle in itself.

    Eh, I guess there are just no magic bullets to boat building. So a chined hull and KSS and plywood and strip planking where needed is already the fastest methods?
    Probably the whole cabin is where I could save the most build time. Maybe simplify the design and make it less elaborate.

    Thanks again! Btw I was interested in local wood only to see if I can buy "unprocessed" and save on material. The prices I've seen so far in online shop are kind of outrageous.
     
  14. Rumars
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    Rumars Senior Member

    Yes there are no magic bullets. Could your ideea of female cold molding work? Yes, but it's not really saving anything and the machine needed to do this would be very hard to justify. It woud have to cut the veneer on the spot since you can't really predict how a piece of wood will bend. Then it would have to remove the piece, coat both surfaces with epoxy, put it back, fix it in place, and apply pressure until cured. You can pay some guys for a lot of years before it makes sense.
    Take a look at this film of hot molding a dinghy. What could you improve now?



    You could CNC the veneer batches but it's not quicker or cheaper. You would use an air powered staple gun with plastic staples that you can leave in. You would use epoxy for glueing and automate the glue coating station like they use when making prepreg. You would still want to autoclave the hull to speed up and postcure the epoxy so maybe using a phenolic resin is still best because it's cheaper. And you would probably use an automated paint robot for varnishing.
    Keep in mind that all this is for series production. Building a few units from a design it's cheaper to pay the human than inverst in automated tooling. You invest only in tooling that is not related to a specific design so you can keep using it.

    What's cheapest depends on location. Europe has a good supply of sliced veneer, so prices are reasonable. Epoxy is also reasonable, so cold molding and strip planking with local woods is cheap. Good quality light plywood is not so cheap. Rot resistant light wood (WRC for example) is not cheap. Prices also depend on purchased quantity and who purchases them.
    What's fastest depends on how the hull was designed. If it's designed with the materials shape limitations in mind and optimized for a specific tehnique then it's fast. If the interior is designed to be part of the building jig it's fast. If it's designed specificly for the amateur builder it's fast for him.
     
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  15. fallguy
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    fallguy Senior Member

    Reefie's LB26 - Bateau2 - Builder Forums https://forums.bateau2.com/viewtopic.php?f=12&t=62627
     
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