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Thread: 5mm Plywood Scarf Joint

  1. #1
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    Default 5mm Plywood Scarf Joint

    I am looking for information on how to prepare a scarf joint for 5mm (.197 inches) marine plywood. I am open to all techniques and jigs.

  2. #2
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    Default Re: 5mm Plywood Scarf Joint

    A proper table, align the layers according to the slope you want (12:1 is recommended) then go at it with a belt sander.

    It’s not as difficult as most people make it out to be. Just try it.

    Then arrange the orientation for glueing, soaking the bevels with unthickened slow-curing epoxy before you use the adhesive thickener which is the actual filling glue.

    Then leave it alone for 2 days.

  3. #3
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    Default Re: 5mm Plywood Scarf Joint

    Check out this other thread, talking about the same thing, with several jig suggestions.

    http://forum.woodenboat.com/showthre...rs-I-need-help!

  4. #4
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    Default Re: 5mm Plywood Scarf Joint

    A belt sander rally does make quick work of it.
    Tom

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    Default Re: 5mm Plywood Scarf Joint

    But a low angle block plane is the tool to use. A wicked sharp blade will do that scarf in seconds flat, so quick, so satisfying, so efficient, so non-land-lubbery.

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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by TerryLL View Post
    But a low angle block plane is the tool to use. A wicked sharp blade will do that scarf in seconds flat, so quick, so satisfying, so efficient, so non-land-lubbery.
    Thanks for all replies. I will try the belt sander and block plane and compare.

  7. #7
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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by Tom Wilkinson View Post
    A belt sander rally does make quick work of it.
    Thats my experience too.
    The ply is very helpful at keeping you in check - the parallel lines of the plys are excellent tell tales.

    Note the suggestion was for a 'low angle' block plane, and for ply the 'wicked sharp blade' is important.
    It's all fun and games until Darth Vader comes.

  8. #8
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    Default Re: 5mm Plywood Scarf Joint

    Remove the bulk with the sander, finish with the plane.

  9. #9
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    Default Re: 5mm Plywood Scarf Joint

    Just stack up the planks. There are four layers of 6mm in this stack. They get glued together in pairs to create one plank per side.

    Plank scarfing - 2.jpg

    Stack them with ends offset by the length of scarf that you desire.
    Plane down the ramp that is created by the offset ends.
    The lams in the ply will tell you how flat the scarfed faces are. Keep them going straight across the plank widths. Its really rather easy to do this.
    I use a plane. I cannot assure control using a belt sander although some can. More power to them. The plane is fast enough.
    After planing smooth I scratch the daylights out of the faces using a multitool blade as a scraper. This gives a good toothed surface for the thickened epoxy.

    Jeff

  10. #10
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    Default Re: 5mm Plywood Scarf Joint

    before you start cutting w/ either method make sure to have your sheets face to face so they come out to your liking

    whether it be color matching or smooth vs knotty sides

    you will be glad you thought it out

    sw
    "we are the people, our parents warned us about" (jb)

    steve

  11. #11
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    Default Re: 5mm Plywood Scarf Joint

    Just in case you don't need to (or don't want to) plane a stack of pieces, it worked for me to use one piece of ply as guide and clamp when cutting the scarf on a plank. Set it back from the edge to the distance that gives the slope you are going for (I used 8:1, seems plenty strong). Working alone, I had to glue the plank scarfs on the boat (at 2 per plank), and each piece had to be at an angle. This method made it easier than scarfing a stack.

    Last edited by rgthom; 08-04-2020 at 04:26 PM. Reason: typo

  12. #12
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    Default Re: 5mm Plywood Scarf Joint

    You are going to be gluing into end grain. First coat with unthickened epoxy, allow to soak in. No need to scratch or tooth the surface, the end grain is going to have lots of holding power. Then use thickened epoxy to complete the joint, while clamping. Brads or staples to keep the joint from slipping. Easier done than said.

  13. #13
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    Default Re: 5mm Plywood Scarf Joint

    Keep coating the end grain. when the plywood stops absorbing, THEN apply the epoxy/flumed silica and clamp

  14. #14
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    Default Re: 5mm Plywood Scarf Joint

    Don't I understand english?
    Didn't I just say that?

  15. #15
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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by Dave Hadfield View Post
    A proper table, align the layers according to the slope you want (12:1 is recommended) then go at it with a belt sander.

    Itís not as difficult as most people make it out to be. Just try it.

    Then arrange the orientation for glueing, soaking the bevels with unthickened slow-curing epoxy before you use the adhesive thickener which is the actual filling glue.

    Then leave it alone for 2 days.
    I used a proper table and low angle block plan with a sharp blade. The task went well. I will epoxy the scarf next.

  16. #16
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    Default Re: 5mm Plywood Scarf Joint

    Great idea to secure the slopes pieces to keep them from sliding.

  17. #17
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    Default Re: 5mm Plywood Scarf Joint

    I re-starting my Rascal build. I have been working away from home for 3.5 years. Hard to work on the boat with only weekend trips home. The traveling is over. Time to focus on the boat.

  18. #18
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    Default Re: 5mm Plywood Scarf Joint

    But a low angle block plane is the tool to use.
    Yup. Its only 5mm ply.

    Stagger-step the ply at the end of a work table. Make sure the table is firm and does not let your work sag as you apply pressure/ weight.Set one piece even with the edge of the table. Place the other piece 60 mm back from that. Clamp tight. You can even use screws and fill the holes later. Then just plane away the step. The plies will guide you--keep them straight and your cut will be good.

    scarf+1.JPG

    scarf+3.JPG
    scarf+4.JPG
    scarf+--wet+glue.JPG

    finished+scarf+3.JPG

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  19. #19
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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by upchurchmr View Post
    Don't I understand english?
    Didn't I just say that?
    .....I was emphasizing the need to THROUGHLY fill the end grain it was unfortunate that you found it irritating. it was NOT meant to be.
    Last edited by the_gr8t_waldo; 08-04-2020 at 06:37 PM.

  20. #20
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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by the_gr8t_waldo View Post
    .....I was emphasizing the need to THROUGHLY fill the end grain it was unfortunate that you found it irritating. it was NOT meant to be.
    Overt communication is good. It emphasizes the point. Thanks for all the input. Based on all the input, I have a successful scarf joint.

  21. #21
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    Default Re: 5mm Plywood Scarf Joint

    It worked exactly as you outlined.

  22. #22
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    Default Re: 5mm Plywood Scarf Joint

    I didn’t find it necessary to scarf any ply on my rascal. The shape will not take sheets of ply very well for the most part. In fact at the forward section I was down to maybe 4” strip slayed diagonally. (All the topside planking was laid diagonally) What section are you doing?
    Tom

  23. #23
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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by Tony Maness View Post
    Overt communication is good. It emphasizes the point. Thanks for all the input. Based on all the input, I have a successful scarf joint.
    Nice one!
    It's all fun and games until Darth Vader comes.

  24. #24
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    Default Re: 5mm Plywood Scarf Joint

    I am scarfing the 5mm plywood for the keel pad. The keel pad was longer than my 8 foot sheet of 5 mm plywood. Did you have longer plywood for your keep pad?

    Thanks

    Keel Pad.jpg

  25. #25
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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by Tony Maness View Post
    I am scarfing the 5mm plywood for the keel pad. The keel pad was longer than my 8 foot sheet of 5 mm plywood. Did you have longer plywood for your keep pad?

    Thanks

    Keel Pad.jpg
    If I remember correctly I did two layers and staggered the joint. Nothing wrong with scarfing it though, and I might do that if I build another. Considering a stretched version with a race motor.
    Tom

  26. #26
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    Default Re: 5mm Plywood Scarf Joint

    You built and excellent Rascal boat and shared a lot of your knowledge of that build with the Wooden Boat community. Thanks

  27. #27
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    Default Re: 5mm Plywood Scarf Joint

    I will be looking g for a source of 1/4 inch mahogany or Sepele for the cover boards or outer planks. I do not have the capability to resaw thick planks. Where did you obtain your boards and in what lengths?

  28. #28
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    Default Re: 5mm Plywood Scarf Joint

    I resawed all mine. If I remember right I used 12’ boards and butted the seams. No issues with it at all. Let me know what you find for planking stock/prices. You could probably buy a saw and a good resaw blade for what they will want for 1/4” stock. My blade was about 215.00 but worth every penny.
    Tom

  29. #29
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    Default Re: 5mm Plywood Scarf Joint

    Quote Originally Posted by Tony Maness View Post
    Based on all the input, I have a successful scarf joint.
    AND a new skill you’ve learned in your kit!

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