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When to make a haunch on mortise and tenon joints

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  • #121291
    wotaewer
    Participant

    I was wondering why on some projects Paul uses mortise and tenon joints with a hauch and on some as this one there is no haunch – even though the joint and function seems to be very similar.
    There are no haunches on the bench stool and the occasional table, however there are haunches on the coffee table and the sofa table.
    So is there any rule or design consideration when to use haunched mortise and tenon joints?

    #121300
    Joe Kaiser
    Participant

    A haunched tenon adds rigidity to the joint. I am not 100% sure on when to use it, but I would assume whenever you need the extra strength. A coffee table might night the extra strength at the join whereas a smaller occasional table won’t

    Seattle, WA

    #121313
    chemical_cake
    Participant

    Where you will consistently see a haunch is in two places that I can think of:

    1. Where the mortised member has been grooved, and the haunch is used to fill the groove;
    2. Where the tenoned and mortised members finish flush on their outside faces, in which case the haunch resists any tendency for the tenoned member to twist or cup.

    Outside of these two situations a haunch is often used, as has been said, for strength and rigidity, however its use in practice is more patchy. It represents a best-case scenario for mortise and tenon joinery on an outside corner, the complication of which can be done away with in some classes of work according to the judgement of the craftsman.

    On the specific examples you have given, Mr Sellers has said he is producing a faithful reproduction of the occasional table, and the original craftsman used no haunches on his tenons. If I remember, on the bench stool, Mr Sellers did say the haunches were not necessary, but I can’t remember if any explanation was given.

    Hope that helps.

    Matt

    Southampton, UK

    #121322
    Mark Armstrong
    Participant

    On the whole haunches are used on corner where the apron goes in to the leg or a rail into a style of a frame work or a door.
    On door construction you even have hidden haunches on middle and bottom rails because of the use of double tenons because the width of the rails are normaly bigger than top rail.
    There are some rules of thumb for mortise and tenon joints normally a tenon should be 1/3 thickness of timber but this not often the case in a door of 1 3/4″ thickness a tenon would be only 1/2″ so just under 1/3 thickness. You defiantly do not want to make the wider than a 1/3 thickness as this woul make mortise walls too thin at least for door construction. I Think there is a bit more leeway for furniture.
    The tenon should not exceed five times the tenons thickness.
    This is to overcome tendency for a wide tenon to buckle also reduce risk of effect of shrinkage.
    In most situations I like to use a haunch on a corner section. Sometimes design aspect of a project a haunch tenon may not suit.

    Dagenham, Essex, England

    #121368
    wotaewer
    Participant

    ok, thank you for your replies. I think I understand it a little bit better

    #121408
    Matt McGrane
    Participant

    @wotaewer – I remember PS saying something about the coffee table could get dragged around the floor, putting great stress on the leg-to-apron joints. My thought is that the haunch is used where the builder thinks there will be added stress. The relatively heavy coffee table might get dragged across the floor, whereas the occasional table (with no haunch) is light and easily could be picked up and set down in a new location. I’m not too familiar with the sofa table project yet, but my guess is that with relatively long legs that could really torque the joint PS might have been concerned with stress of those joints even though it is probably fairly light.

    Just a few thoughts. Hope that helps.

    Matt, Northern California - Started a blog in 2016: http://tinyshopww.blogspot.com/

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