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  1. #1
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    Mar 2008
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    Default Gluing without clamps - The rub joint

    A while ago I read an article by Paul Sellers about spring joints. In it, he made an almost off-hand comment about the once common practice of edge joining panels without any clamps at all. Given the context of the comment, I'm not sure if this technique only applies to animal glues which, in his words, " ‘snatched’, which meant that during the cure the glue ‘pulled’ surfaces together". Moving forward several months, yesterday I was joining up some small lengths of Spotted Gum for tall drawer fronts, and found myself clamp-less, owing to my wife working on a large project which required most of the suitably sized clamps. Paul Sellers' words found their way from my long term memory to my present consciousness, and a light bulb illuminated.

    Now I don't have any hide or fish glue (is fish glue even a thing any more?), so decided to attempt rub joining the pieces with plain old PVA white glue (my wife had the Titebond III on the other side of the shed, whilst the plain PVA was on a shelf right behind me - I like to think this is a sign of someone naturally operating at peak efficiency, rather than laziness).

    20191005_195211-1024x768.jpg

    Before I get underway, for those unfamiliar with the rub joint, here's Paul.
    This is where we rub the two glued edges to be joined along one another moving one back and forth against the other, which is held in the vise, until the glue is evenly and thinly dispersed. During this process the glue gets as thin as possible between the surfaces and then, at a certain point, the glue ‘grabs’ or ‘snatches’ and the parts no longer move.


    Leaning two or three sticks inclined and sighted in against one another (to ensure no twist in them) against a wall was a resting place for the glued boards to stand leaning in toward the wall on edge but flat against the sticks. The boards were left unclamped until the next day when full cure was achieved.
    Paul Sellers, 2014 ( Questions Answered - Spring Edge Edge-jointing Boards - Paul Sellers' Blog )


    The panels I made up were each comprised of two boards 300 x 85 x 18 mm, with the join on the 18 mm side.

    20191005_195131-1024x768.jpg

    After a bit of preparation on the other draw components in the workshop this morning, I changed my mind and decided to forgo the spotted gum as the fronts. I was thus left with two panels glued up with a new method that I no longer needed. Why not test the strength of the joint.

    To test, I clamped one board to the end of my bench, with the joint just proud of the edge.

    20191005_112032-1024x768.jpg 20191005_112045-2-1024x768.jpg

    But what to do for weights? Fortunately there are a bunch of dive cylinders that are currently living under the table saw wing, and being filled to 240 bar they weigh in at a nice even 20 kg each (give or take 50 g). Note the strategically placed blue matting below to cushion any falling tanks.

    20191005_112501-1024x768.jpg 20191005_112525-1024x768.jpg 20191005_112534-1024x768.jpg

    20 kg? All OK.

    20191005_112613-1024x768.jpg 20191005_112632-1024x768.jpg

    40 kg? All OK.

    20191005_112718-1-1024x768.jpg

    60 kg? Still no issues.

    20191005_112858-1024x768.jpg 20191005_112910-1024x768.jpg

    Oh dear, while I had more weight, there was no more room on the board to hold additional cylinders. So what to do? Fortunately there is one more heavier weight at hand.

    20191005_113108-1024x768.jpg 20191005_113333-1024x768.jpg

    For the record, I was wearing steel capped boots, and heavy trousers.

    In conclusion, I have decided that the rub joint is remarkably effective.

    Lance

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  3. #2
    Join Date
    Dec 2005
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    South Australia
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    Default

    I have been using rub joints on and off for 40+ years I did not realize it was not common practice it was part of my apprenticeship training

  4. #3
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    Feb 2007
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    blue mountains
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    Default

    I have done this with PVA also on small projects as it is quick to do. Never got around to testing it so thats good info to show how well it works. I would be interested to know just how big a joint would be possible with this method. Anyone out there done a big rubbed joint?
    Regards
    John

  5. #4
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    Dec 2005
    Location
    South Australia
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    Default

    About 10 years ago I used this method with a mate in Bordertown to glue up a table top appr. 2m x 1.2m, 6 boards still going strong after daily use

  6. #5
    Join Date
    Nov 2004
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    Brisbane
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    Default

    Hmmm. I've heard of the rub joint with hot hide glue (I've used this myself) but not with PVA. I wonder what is happening that makes this work.

  7. #6
    Join Date
    Mar 2008
    Location
    Hobart, Tas
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    Default

    Quote Originally Posted by China View Post
    I have been using rub joints on and off for 40+ years I did not realize it was not common practice it was part of my apprenticeship training
    China, do you still routinely use rub joining? I don't dispute that it's not common, I'd just never come across it before.

    As you were taught the technique, I would be interested to hear when edge joining a couple of pieces, what would you consider when deciding whether to clamp or rub?

    Also, apart from the fact that hide glue pulls together as it cures (so I've read), is there something else that makes it more suitable than PVA (or other glues) for rubbing. Is/was rubbing other glues also common practice? If not, do you know why?

    Share your knowledge with us oh learned one.

    Kind regards,
    Lance

  8. #7
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    Dec 2005
    Location
    South Australia
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    Default

    I don't use hide glue, unless it is a specific antique restoration. Hide glue does not really pull together it just sets very quickly, yes many times if I am just joining two small boards I will use the rub technique, on larger items cramps assist in keeping things in place, the basic principle is the rubbing removes the air from the joint just as cramps do, air is what pushes the join apart
    Cramping a join also allows you to make the join and move it aside to do something else, with a rubbed joint you need to let it cure before you can move it.

  9. #8
    Join Date
    Aug 2011
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    bilpin
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    Default

    Fifty something years ago I made a drawing board at school. PVA glue and rubbed joints. I still have that board today. Joints are as tight as when I made it.

  10. #9
    Join Date
    Mar 2008
    Location
    Hobart, Tas
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    Default

    Thanks for a really informative reply China.

    Quote Originally Posted by China View Post
    the basic principle is the rubbing removes the air from the joint just as cramps do, air is what pushes the join apart
    Hmmm, that's really interesting, and makes me look at gluing slightly differently. For whatever reason I have always assumed that glue needs pressure to work effectively. My experiment and your responses shows that to be a dubious assumption to have had.

    Kind regards,
    Lance

  11. #10
    Join Date
    Aug 2010
    Location
    ACT
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    80
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    2,438

    Default

    Hi,
    Yes I think removing air is the idea, another thing I have seen is pulling the joint open for a few seconds after the initial put together.
    Regards
    Hugh

    Enough is enough, more than enough is too much.

  12. #11
    Join Date
    Jun 2018
    Location
    Melbourne
    Posts
    31

    Default

    I have found that Titebond 3 works well on a variety of timber and chipboard types with this type of joint.

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