Fillet Question

Discussion in 'Boatbuilding' started by ddrdan, Dec 17, 2011.

  1. ddrdan
    Joined: Mar 2009
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    ddrdan Junior Member

    Are epoxy fillets just considered the easier way, or can a wood fillet with a convex radius be bed in epoxy and achieve the same purpose?

    The reason I ask is I have virtually no curved areas in the hull and lots of scrap to make wood fillets from. And, I've read that sharp bends in fiberglass are weak points. So, if I make a wood fillet with a radius larger than the common epoxy fillet, wouldn't that have less fiberglass stress at the joint also?

    I started doing epoxy fillets and found it to be messy, complicated mixing, more sanding, and a general pain in the ***. I'm not trying to redesign the wheel here. Just trying to avoid the PITA process of over 600lf of epoxy and wood filler fillet!! :)
  2. michael pierzga
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    michael pierzga Senior Member

    What type of joint are you talking about ? Certainly a molded wooden cleat is strong and will work for many joints. Time consuming to construct molded cleats and complicated by temporary fastenings to fix the piece while the epoxy cures. Also remember that timber does not like to be buried under epoxy glass fabric then get wet. Plywood, because of its grain structure, is tolerant of moisture , timber is not tolerant, expands and contracts, wicks moisture and will deteriorate a glass fabic covered joint over time. Many builders refuse to encapsulate timber.
  3. LP
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    LP Flying Boatman

    I can't speak for whether structurally this would work in your application. Most likely you will be ok, but it make me question whether you going about filleting in an efficient manner.

    A little bit preparation in advance of filleting will save a lot of mess and headache. To me, it will be less work than the up front work needed to make your wooden "fillets."

    First and foremost: mask off the fillet area. Take the tape right to the edge of where the fillet blends to the adjacent surface. When your fillet is in place and most of the excess is removed, pull the tape and you've got a nice, well defined fillet edge. While the fillet is still uncured lay in your glass tape and wet it fully with unthicken epoxy. Filleting is a bit of drudgery, but this way lessen the mess and the glass tape gets worked into the fillet a bit. If needed, you can run a gloved finger over the taped fillet to smoothed any irregularities.
  4. lewisboats
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    lewisboats Obsessed Member

    What LP said...exactly. No muss no fuss and very little bother.
  5. michael pierzga
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    michael pierzga Senior Member

    Making fillets is a skill. Ive never perfected it... I must always cleanup with a wood scraper ground to the correct shape.

    If you search Manies micro cruiser thread you will see that he was making prefect fillets with peel ply and an appropriate radius roller. Ive never tried it , but it looks logical and to be a great labour saver.
  6. TeddyDiver
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    TeddyDiver Gollywobbler

    Short answer: Yes
    and a good example: Wooden fillets are actually easier in "difficult to reach places" like inside compartments throw inspection hatch openings. Just dip the (triangular) wooden fillet piece in "mayonaise" epoxy bog and put in place. Easy to do without seeing the place itself, just with the feel of finger tips. When all the pieces are in place brush "ketchup" epoxy over and place biax strip over the fillet and the sides of the fillet. A bit brushing and a couple of coats over with epoxy and done with it. There's no need to radius the wood, just enough mayonaise and gentle brushing and you get good round shape. I mostly cut the wood end grain when doing this.
    BR Teddy
  7. messabout
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    messabout Senior Member

    I suspect that using a wooden cove strip and covering it with glass will be more work and aggravation than using the epoxy fillet methods. If I was going to deal with a joint such as a chine, I'd use a chine log and call it good. Perhaps saturating the wooden chine log but not covering with glass. Alternatively use epoxy fillets.

    A forming tool as simple as a credit card will make nice fillets. The trick is to control the tilt of the card or scraper. If it is tilted toward the direction of motion, it will form a larger fillet than if held perpindicular to the surfaces to be joined. Once the fillets are in place cover with glass tape, saturate the tape. (dont over do it) and then cover the whole sticky mess with strips of visqueen. You can now squeegee out the excess and clean up the overflow. This will give you a smooth finish, take the bubbles out of the tape epoxy, and eliminate a ton of sanding. Pull the visqueen off after the expoxy has partially set up but before it is fully hardened. A cheap way to get a nice job. Warning; do not try to re-use the visqueen strips. They'll be a ***** to remove if you do.

    I suggest that you experiment with some scrap ply before tackling the whole boat with a filleting scheme.

    For the sake of starting an argument, I will claim that epoxy fillets will be much more reliable, strength wise, than some sort of glass covered cove strips.
  8. michael pierzga
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    michael pierzga Senior Member

    Epoxy is expensive when compared to wood. Epoxy is messy.

    Also Remember its not always possible to fillet and glass in one operation. Either the project is to big for one man or perhaps built with thin plywood where the whole structure is unstable until the fillet cures.

    all fillets need not be glass taped. I really liked Mannies peel ply fillets. Need to give them a try
  9. philSweet
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    philSweet Senior Member

    Forget using wood dust for fillet. If you were making your own from sander dust it is probably too coarse (120 grit or finer hardwood dust ok, don't use softwoods at all) and besides that it is a terrible thixotrope. Get fulminated silica (Cabosil, Aerosil, etc) that's what you need. You can mix it to the consistency of cold peanut butter if you need to. Old light bulbs make good filleting tools. Also, buy a dozen yellow plastic 5" spreaders and cut them to the profiles you need. They can be reused many times. It would help greatly if you could find someone to show you the feel of it. You'd probably learn as much in an hour as you will figure out in a year.

    It should go on looking like this-

    Attached Files:

  10. CatBuilder

    CatBuilder Previous Member

    I used to use a spray paint can lid. Now, I have been cutting a piece of PVC pipe off and it works wonderfully. Cove joints are pretty straight forward. Mix up some fairly stiff bog, so it doesn't sag, squirt it into the gap with a pastry bag. Then, drag your round object over it and PRESTO!

    Perfect cove that reaches all the way under the bulkhead.
  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    Having watched a buddy struggle with epoxy fillets - he had built several boats before, so his problems were not due to inexperience - I decided to go with chine logs for my first boat. I don’t know what stage your build is but if you are already working on filleting perhaps you should probably continue with that using the above advice.

    However it shouldn’t be too difficult or time-consuming to make wood fillets. To size them I would test the ply first to see what width joint and fillet will exceed the strength of the ply, usually around 3 times the ply thickness. Then just router the cove profile* on the edge of a plank of the right thickness and part off with a saw. Chop into convenient lengths and glue in place, staple as required.

    * a cove profile is what is used for epoxy fillets but is not the most efficient, that would be a quarter-round. I use a triangular section as a practical compromise which can be planed on the plank edge. Provided the test samples work I know the finished job will be strong enough with no need for glassing.

    My chine log approach used on my 3 and 5-planker designs is described below FYI:

    I glued the chine logs using Titebond III to the odd numbered planks (e.g., sheers and bottom for a 5-planker), installed those planks over the mold, planed bevels for the other planks and epoxied those. Finally the exposed edges are planed flush. This gives a neat appearance with much less work than filleting.

    The method is similar to glued lapstrake but the pre-glued logs stiffen and support the edges of long floppy planks during planing and make them easier to handle. The logs are far lighter than would be used for a ply-on-frame build; the wood has more volume than a concave epoxy fillet but since it is less dense the extra weight is negligible.

    This system has worked well for me. Caveat: pre-gluing the logs to the planks is more suited to a small boat than a larger one, since the planks with the logs glued on may become too hard to bend. It does not work on a boat with many planks as the bevels become too wide.

  12. waikikin
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    waikikin Senior Member

    Reads like a chine log or stringer with a round over......
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