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Thread: wood lamination bending

  1. #1

    wood lamination bending

    Need to pick some minds of those experienced in wood lamination bending.

    As I have mentioned I am in an on going project of reconstructing a woodbody Model T Towncar. I need to make forward doors to fit the existing framework.

    I know the ins and outs of the laminations but I am in a confusion as to how much allowance for "Springback" when the piece is cured and removed from the jig (which I have yet to make) I need to incorperate that tollerance into the jig.

    Here is a drawing of the desired door, I will need a 1/8 to 1/4 in clearance and try to keep it constand and at a minimum. Any help greatly appreciated.
    Attached Thumbnails Attached Thumbnails door 2.JPG  

  2. #2
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    what part are you bending bill?
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  3. #3
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    General rule of thumb is that the thinner the laminations (and the thicker the finished piece) the less springback.

    If you can get your lams down to about 1/16", and your finished piece will be an inch and a half or so, there will be very little springback.

    I recall reading somewhere that Mr. Ford used a lot of Ash in builting his T's. Is that what you'll be using? If so, you'll find that it bends quite nicely. Use a powder/water mix of urea formaldehyde glue and it'll be water-resistant and also won't creep. It'll also have the longer open time you'll need for doing the 25~30 lams you'll need.
    Jim D.
    Adapt, Improvise, Overcome!

  4. #4
    The piece will be 3/4 thick by 2" wide, will have to shape to a slight taper on the inside so I am starting with 1" thick. best I can muster is 1/8" laminants. Yes, Ford used a lot of Ash but it was because he had family property with a large Ash forrest. Most of this car is Maple with Cherry accent pieces, (Which was the practice at the time.) The rear doors are laminate bent from red oak, but the original builder made the frame as well as the doors and could make allowances , I have to fit to an existing frame.

    I have been successful with Polyurethane glue, in the past. I had a complete failure with powder/water mix of urea formaldehyde glue a number of years back where I made an endgrain cutting board and when it was shipped, it arrived as a box of square pieces of wood. thanks for the suggestion, will consider...

    I will need to bend the two radius portions (the bottom may not be flat as well). Will start on the jig soon, (going out of town for a funeral) that is why I was asking about the spring back. I can always try a "Prototype" and if it springs much I can trim the jig to allow for it, may waste a bit of wood and effort and such but.... Wood is wood and would or would not surprise me with the results
    Attached Thumbnails Attached Thumbnails door222.jpg  

  5. #5
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    for the curved members of the frame i wouldn`t do a bent lamination, i`d do a brick stack and saw `em out with the bandsaw...they`ll be painted and a brick stack using 1/4" pieces would be stronger than ol` henry used and take less than 1/2 the time of doing a bend.
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  6. #6
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    Bill, I asked this question on another forum a couple years back and this was the answer I got. I used it and it came out almost dead on !!

    Tony,
    Here is some info from the May issue of American Woodworker on bent wood laminations that may be helpful.

    Lamination ...........Ply
    Radius ...............Thickness
    ------------------------------
    2-4" ..................3/32"
    4-8" ..................1/8"
    8-12" .................3/16"
    > 12" .................1/4"

    Note: Hard or stiff wood such as maple may need to be cut thinner than
    soft woods such as pine.

    As far as springback, they say: "You can never predict exactly how much springback will occur. But you can compensate for springback in your form design with this formula.

    Rfinal is the radius you want for your bent lamination; (n) is the number of plies; Rform is the radius of your jig.

    Formula: Rfinal(n-1)/n=Rform

    Example: A 5" radius, 10 ply lamination 5"(10-1)/10 = 45/10 = 4.5"

    Tony, BCE '75

  7. #7
    Quote Originally Posted by tod evans View Post
    for the curved members of the frame i wouldn`t do a bent lamination, i`d do a brick stack and saw `em out with the bandsaw...they`ll be painted and a brick stack using 1/4" pieces would be stronger than ol` henry used and take less than 1/2 the time of doing a bend.
    I am confused...

    Are you talking about this , in the picture? wouldn't that make for a lot of short grain and fragile pieces?
    Attached Thumbnails Attached Thumbnails door333.JPG  

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    like this jamb bill.....only use thinner segments so as to have more "bricks" in the stack.
    Click image for larger version. 

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    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  9. #9
    Quote Originally Posted by tod evans View Post
    like this jamb bill.....only use thinner segments so as to have more "bricks" in the stack.
    Click image for larger version. 

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    OK, I see, makes sense, Will consider it... assume you need to figure the miter of each segment to conform to near the Radius of the curve. But how do you clamp it?

  10. #10
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    Quote Originally Posted by Bill Simpson View Post
    OK, I see, makes sense, Will consider it... assume you need to figure the miter of each segment to conform to near the Radius of the curve. But how do you clamp it?
    bar clamps.....pretty easy........much easier than a form and plys.
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

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