Resawing veneers for cold-molding ?

Discussion in 'Wooden Boat Building and Restoration' started by mcm, May 25, 2012.

  1. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Are bandsawed resawn veneers GOOD ENOUGH to use in cold-molding, or must the veneers be peeled from rotary peeler machines ?

    I notice that the grain orientation of red cedar veneers that i resaw from quarter sawn stock is different from store bought peeled veneers.
     
  2. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    I do not see why not, the veneers are essentially fillers that separate the composite skins on either side of the build-up. Most of the strength of the hull comes from the skin, not the core. Consider that foam-core-fiberglass-skin hulls are structurally similar, except the cedar is stronger than the foam, so it can be thinner. I really doubt there is any difference in bonding strength.

    The core build-up has to take both shear and cross grain compression from impacts and through-hull fasteners. Be it sawn or peeled, the difference in properties is small. If anything the cross grain sawn veneers should have better compression strength than from peeled plys. Shear strength should be similar, but the shear loads on the core would be very small anyway (again consider the foam analogy, foam has even lower shear strength).

    The only down side is the cross grain cut veneer may not take as tight a bend as peeled veneers. But that you can likely deal with by careful application, or using a mix of sawn and peeled layers in any tight bend radius area.

    I would not hesitate to use them at all, and I am saying this as an experience structural engineer.

    what are you building?
     
  3. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Petros,

    That's encouraging to hear that veneers sawn from quarter sawn timber is equal or even better than conventional rotary peeled veneers.

    However,

    In cold-molding veneers make up the entire hull by diagonally laminated layers of veneers, with only a very light fiberglass top layer for abrasion resistance only.

    Would your opinion still stand in those circumstances ?
     
  4. Corley
    Joined: Oct 2009
    Posts: 3,770
    Likes: 189, Points: 63, Legacy Rep: 826
    Location: Melbourne, Australia

    Corley epoxy coated

    fibre orientation is more important than whether the veneers are peeled or cut you simply want the fibres to run in the right direction. The crossed veneers provide the main structural strength not the skins in the case of cold molding often the completed hull simply carries a light sheathing for protection.
     
  5. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    OK Corley, but if it is as important as you say then the question still remains,

    Will the fiber orientation of veneers sawn from quarter-sawn stock run in the right direction to create a strong cold-molded hull or not ?
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 480, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Resawn veneers would be my first choice, compared to rotary peeled. The grain and fiber orientation is better in regard to eventual hull shell stiffness, assuming reasonable alternating diagonal planking of sufficient thickness or additional reinforcement. There are about a dozen different cold molded methods, some more forgiving then others in this regard. What is the general hull shell veneer schedule?
     
  7. Corley
    Joined: Oct 2009
    Posts: 3,770
    Likes: 189, Points: 63, Legacy Rep: 826
    Location: Melbourne, Australia

    Corley epoxy coated

    Quarter sawn stock will be fine as long as the grain is straight and clear. The orientation in which the stock is sawn should not be critical as long as it's inline with the veneer as the method adds dimensional stability with the diagonal orientation of the veneers layers.
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 480, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Also make sure it's actually resawn stock, not just band sawn. A band saw as a 1" (or so) blade, while a resaw machine has a 3" or wider blade. Huge difference in the quality of the veneers off each type of machine. If it's band sawn, then you have to mill quite a bit off it, just to get a uniform thickness. Resawn stock will need much less removed.
     
  9. Oyster
    Joined: Feb 2006
    Posts: 269
    Likes: 9, Points: 0, Legacy Rep: 104
    Location: eastern United States

    Oyster Senior Member

    If you only have a conventional bandsaw, bandsawing is not always a straight foward method for resawing true veneers and can cause a lot of waste and still need to plane smoothe each and every veneer to get a uniform thickness. One method that I do use is if I have decent veneers after bandsawing is to run them thru a drum sander. If you do not have one in most cases a local cabinet shop will and you can pay them a few bucks and true their thickness up. Keep in mind whatever unfairness in thickness can telegraph out to the surfaces causing a lot of fairing before a final finish is applied.



    Quality resaw bandsaws use very wide blades and also creates a lot of waste because the blade needs to be pretty rigid to keep wondering to a minimum. You will need to check the trueness with some stock and quite possibly set up a guide that may not reflect a complete right angle to the saw's top and blade.


    If you have a quality 10" table saw you can create quality veneers up to six inches in most cases with much less work. With a good unifence and an additional plank fastened to it just saw the solid stock with the blade up full throw, which is normally around 3" and flip it over and finish the veneer cut. Use a quality kerf blade which is much thinner than a carbide tip blade for most jobs which saves you a lot of wood.If you get some uneven seams. Do some test runs and make sure you are getting a correct 90 degree . For more accuracy in the sawing process run the stock thru a drum sander or a surface planer before each cut.
     
  10. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    My 1hp, 14"(360mm), standard bandsaw, with a quality 1/2"(13mm) resaw blade and squared resaw fence, saws perfectly exact 1/8"(3mm) veneers up to 6"(154mm), and cuts like a hot knife through butter.

    But the face of these resawn veneers is all edge-grain, and i was thinking about the problem of shear strength of a veneer that is all edge grain.

    Individually i could put a length of an 1/8" veneer against the edge of my table and easily spit it along the grain.

    But, with a laminating schedule of 4) 1/8" veneers (13mm) diagonally laid, maybe my concerns are misplaced.
     
  11. garyohv
    Joined: May 2012
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Oregon

    garyohv Junior Member

    I use quarter sawn timber to resist forces perpendicular to the growth rings. Layering a typical quarter sawn wood section on a hull does not achieve that orientation. Peeled or sawn verneers (with rings parallel to the hull) would be slightly stonger... and similiar to the way the tree grew to resist it's bending. I think quater sawn could split easier. I do not see an end grain problem.
     
  12. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Exactly Garyohv,

    The growth rings on resawn veneers won't be perpendicular to lateral forces against the hull.

    That's my concern.

    They would however be perpendicular to the up and down sagging and hogging from wave crest to wave trough.

    The question is: are resawn veneers vs rotary peeled veneers strong enough to use in cold-molding or not ?
     
  13. Corley
    Joined: Oct 2009
    Posts: 3,770
    Likes: 189, Points: 63, Legacy Rep: 826
    Location: Melbourne, Australia

    Corley epoxy coated

  14. Oyster
    Joined: Feb 2006
    Posts: 269
    Likes: 9, Points: 0, Legacy Rep: 104
    Location: eastern United States

    Oyster Senior Member

    When cold moulding a hull, the multi=direction of any and all grain pattern in multiple layers is only part of makes this type of hull sea worthy The internal structure is really the key element for a sound hull. Plywood is a good example of what amounts to weak veneers because of the thickness or lack of cut at random without one particular consideration and glued to together to make a size appropiate strong component. I would not worry as much about the actual grain pattern as much as building the actual hull with finished scantlings that will work with the internal components all dependant upon the designer's guidlines.
    This is an example of a recent build of white cedar veneers sawn at random and glued with epoxy, a proven method for a lot of boats.

    [​IMG]

    Plywood veneers are used in many ocean going boats without a single worry of grain orientation as long as the veneers are continuous and solid in the inner cores for a particular veneer thickness.
     

  15. mcm
    Joined: Sep 2006
    Posts: 158
    Likes: 1, Points: 18, Legacy Rep: 26
    Location: Port Townsend, Wa., USA

    mcm Senior Member

    Corley, thanks for the link.

    And yeah, you're right.
    They say resawing veneers from quarter-sawn lumber results in a more stable veneer that expands and contracts less than rotary peeled veneers.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.