Bridle vs Mortise & Tenon joint

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  • #644237
    Bill Hall
    Participant

    Is there a reason I would choose to use one over the other for particular applications?

    Is one stronger than the other, maybe easier to do or maybe preference in appearance?

    #645605
    David Barker
    Participant

    I’m relatively new to woodworking in regards to joinery but a bit of physics can aid in answering this.

    It depends on the application and which direction force will typically be applied to the joint.

    Think of it in terms of 3 dimensional axis X, Y and Z. A mortise and tenon joint will only ever be able to move in one direction on one axis once assembled lets say it was insered on the X axis in a direction of A, it can only be removed by an opposing force on the X axis in direction B. A bridle joint on the other hand can move in one direction on one axis and both directions on another axis once assembled, lets say it was inserted on the X axis in direction A. It can be removed by a force on the X axis in the opposite direction (B) AND by a force on the Y axis in both directions.

    So is one stronger than another? Yes and No. The mortise and tenon restricts the ability for the joint to be compromised by only allowing one direction on one axis for it to to come undone. However if the only force ever applied to the bridle joint (in terms of the example above) is on the Z axis it will have comparative strength to the mortise and tenon.

    A secondary consideration is the surface area that glue will act as an adhesive which is greater on a mortise and tenon joint.

    As I mentioned I’m quite new to joinery so it might be good if someone else who has more experience could also throw in their tupence.

    #645748
    Sven-Olof Jansson
    Participant

    If experience isn’t understood as skills, then I have some on the bridle joint (slip-joint with another – possibly more correct – name. Anyway, here’s my farthing, mainly based on windows and doors.

    Basically, I think the slip-joint is confined to stand alone frames (doors, windows, and [well] frames). It does not seem to be a good alternative for caseworks, as the joinery of any piece to be attached perpendicular to the corner of a slip-jointed frame would damage to the slip-joint.

    Furthermore, its use is probably limited by the size of the frame. Large frames, as front and interior doors, seem to be very keen to twist; probably because of gradients in temperature and humidity along their heights. Wide stiles and bottom rails, allow for tall (often double) tenons, which I believe interlock with the mortices: the rails cancelling the warp of the stiles, and vice versa. The open end of the slip-joint perhaps results in poorer interlocking properties, I guess.

    The slip-joint is quite great for making windows up to a size. One can make the rebates for the panes before cutting to dimension, and then close the gap made by the rebate by shorten the tenons on rebated side to the width of the rebate.

    The strength of both mortice-tenon joints and slip-joints can be enhanced by pegs or drawboring. Please see attached photo of a drawbored century old glazing bar. The window needs to be replaced, but the joinery looks to be …

    Sven-Olof Jansson
    London, UK; Boston, MA

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