Shortening boards with already dry-fitted joints

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  • #714493
    Sven-Olof Jansson
    Participant

    This post is on using scarf joinery to shorten boards with already fitted joints, using 1:2 joint lines instead of 1:8 – 1/10; and the benefits from loose tenons in enhancing joint strength, preventing the introduction of warp, as well as at attaining the desired length.

    With only a memory from Terrie Noll’s “The Joint Book, The Complete Guide to Wood Joinery” (ISBN 91-534-2490-5) of what seems to be an utterly challenging scarf joint (please, see drawing), I went ahead.

    Scarf Joints 1

    Failing at getting a tight joint line by edge planing, and having to add a piece, I used a temporary “shooting board” (please see photo). That did the trick, particularly on the second rail. Probably, it would have been a more challenging task along four times longer edges.

    Assuring the desired lengths could have been lot easier with the use of masking tape, but that only dawned on me when editing the photos. The contraption used is depicted.

    Scarf Joints 2

    By gradually turning the screws of clamps along the axes of the rails, the desired length was established. F-clamps from the sides prevented sliding – widths had to be maintained

    The second joint line looks a lot better. Actually, enlargement of the photo showing the finished results may be required to see it. Number one will go to the bottom back of the cabinet, away from any critical eyes. A more forethinking woodworker would of course have learnt from a prototype…

    Sven-Olof Jansson
    London, UK; Boston, MA

    #714585
    sanford
    Participant

    Thanks for showing this Sven-Olof. I have only seen scarf joints on things like trim in houses. A few questions. Why 1:2 rather than 1:8 or 1:10? The latter give longer glue lines and should be stronger. Also, the little diagram you show is of what I think is called a “nibbed” scarf, or some such, while you made a plain one. I assume the nib serves a function. I would guess it helps with gluing and clamping since you can jam the two boards together along their long axis without them sliding past each other.

    #714722
    Sven-Olof Jansson
    Participant

    You’re welcome Sanford.

    It seemed a good idea to use a sliding bevel to make the 10 mm transfer from edge to edge, and 1:2 appeared more appropriate than 1:1. The loose tenons were added as an reinforcement. Serendipity had it that they made the joinery so much easier. Only when done, did I learn that 1:8 or 1:10 are the more common ratios for scarf joints (and that reinforcements allow for less open angles).

    Supposedly a 1:8 relation would have made the planing more akin to ordinary edge planing to square and straight, but how does one preserve the thin arrow like ends?

    I too believe a nibbed scarf would have facilitated the fitting. However, according Mr. T. Noll, the advantages are that those very thin and weak edges are eliminated, and that (and this I did remember) the nibbed scarf is the most awe inspiring joint, being the most challenging one, demanding the greatest accuracy and precision if a perfect fit is to be achieved. Enough for me to desist any attempts – at least for the time being…

    Sven-Olof Jansson
    London, UK; Boston, MA

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