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    Assembly question.

    I have a 31" x 22" red cedar glue up. The 22" sides are the end grains. I want to attach 4" vertical sides along the 22" sides with rabbet joinery. I was planning on gluing the entire 22" joint. Is that too long when considering expansion? Any ideas opinions, or alternate assembly ideas would be appreciated. All boards are just under 3/4" thick and all surfaces will have 3 coats of polyurethane. Thanks for the help.

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    Re: Assembly question.

    Tom, if you're working off plans would it be possible to post a pic of what you are describing? That may help figure out what the issues will be.

    Basically, is sounds like you're doing the same thing as a bread board end. A cross grain glue up, in which case you definitely don't want to glue the entire 22". The outer edge of the panel will need to float.
    I'll gladly tell you how I do something. Just please don't confuse that with the right way to do it, and almost certainly not the only way.


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    Re: Assembly question.

    Hard to visualize. It needs to float. I'd be looking at pins through elongated holes in the panel, etc.

    A pic would be very helpful.

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    Re: Assembly question.

    How are you planning on attaching the vertical sides, other than just gluing them to the end? The vertical sides, if long grain along the 22" dimension, will not expand/contract but just a very small amount. The glue up will expand and contract at least 1/8" or more, so will buckle or crack if glued to the entire length, or even if just glued to the outside ends.

    Options would be a sliding dovetail, or a cleat screwed under the top with elongated holes to which the vertical end would be attached, but the top can still expand or contract. Attaching the vertical piece to a "bread-board end" would be another option.

    If you want the top to expand evenly on both ends, glue/screw only the middle fastener. If it will be against a wall, and you want any expansion/contraction to only be visible on the back side, screw/glue the front fatener, and elongate the holes for the remaining ones.

    Look for "cross grain joint" if you want to research it further

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    Last edited by Gofor; 01-08-2019 at 01:05 PM.
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    Re: Assembly question.

    stove sink topper design.jpghere is a general pix of my design in sketchup. As you will see, the joint in the sketch is a rabbet. I was thinking of cutting grooves left to right(about every 3-4") full width approx. 80% of the thickness of the wood to help alleviate a majority of the expansion. This will be sitting on a stove or sink. Thoughts?
    Last edited by Temp626; 01-08-2019 at 02:07 PM. Reason: forgot to add photo and additional description

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    Re: Assembly question.

    A couple thoughts:

    The rabbet does not offer any support for lifting the assembly other than the short section of glue, which is an end grain joint. Even if you cut the slots and glue all the way across, there will be little support to lift with.

    I would be afraid that the cedar would crack where you are cutting the grooves. Cedar is soft and crack prone to start with.

    If you are not adverse to metal fasteners, brass screws would provide support, the heads would resist the joint pulling apart outwards, and the holes in all but the main anchor screws could be elongated slightly. The softness of the brass and wood combined will probably allow enough movement that the elongation does not have to be extreme.

    Another option would be to use figure eight fasteners on the underside. However, the shortness of the screws in the underside of the large glue-up portion may not anchor well enough to resist pulling out. Might be hard to find figure eight fasteners that won't rust.

    Third option would be to do a half rabbet (a dado half the thickness of the main panel), or extend the end pieces down below the main panel so the bottom shoulder of the dado would help support the main panel. This would still require some additional screws in elongated holes to keep the joint tight. The advantage of extending the side vertical pieces below the main panel is that it would better prevent the whole thing from rocking if the sink top isn't flat. Its a lot easier to plane off a little of the ends to get things to sit solid, than deal with a whole flat surface.

    Fourth option if you are okay with the ends being proud of the bottom, would be to go with your initial design, but add a cleat front-to-back on the ends. The cleat would be about the same thickness as the side pieces, but twice the width, providing a ledge for the main panel to sit on. Screw/glue the entire length to the bottom of the side pieces, but just screws (with some elongated holes) into the bottom of the main panel to keep it in place.

    With all the above, any glue on the main panel would be limited to about a 3" length, most likely at the back end to prevent the expansion from applying pressure to the vertical joint between the ends and the back.

    Due to the fragile nature of cedar, you may want to consider making the end vertical pieces of a stronger/tougher material such as white oak to add strength to the shoulders of the dadoes if you go that route. However, this may add a lot of weight.

    Now that you have posted a picture, I am sure others will come forth with better advice.

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    Last edited by Gofor; 01-08-2019 at 03:19 PM.
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    Re: Assembly question.

    Make the 4" x 22" vertical sides end grain to match the end grain bottom. Everything will move together.

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    Re: Assembly question.

    I would make a frame and panel surface and finger joint the vertical edges all around. No cross grain anywhere.



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    Re: Assembly question.

    Your SketchUp pic is sure helpful. I've attached a SketchUP version with dadoes instead of rabbets.

    The horizontal 33" long surface fits in them giving good support and stability. If you include the back board shown in your SU diagram you'll get even more support. A little glue or a few screws and your done.

    I haven't figured out to attach an image with the broken system. How do you all it?
    Attached Files Attached Files
    Last edited by Jeff; 01-08-2019 at 05:11 PM.

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    Re: Assembly question.

    I prefer to secure back panels using light gauge brads at regular intervals along each edge. They will still provide added rigidity but the lightweight brads (around 21-23 gauge) are not so rigid as to actually resist movement if the wood really needs to move. I’ve never had any issues with this approach over a good many years.

    You can glue long grain to long grain provided the two woods have similar expansion/ contraction coefficients, but if you are ever to glue long grain to end grain then you generally only want to glue a few inches in the center of the end grain span. But, still, I find simply tacking the back on with lightweight brads to be highly effective and my preferred solution for spans too great to get by with simply glueing.

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    Re: Assembly question.

    Thank you all for the variety of solutions. still not sure which way I will go, but definitely have some options now. Thanks again.

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    Re: Assembly question.

    I like Jeff's suggestion.

    Several ways to do this and account for movement.

    1. Dowels
    2. Screws
    3. Dominoes (IMO ideal situation for a Domino. One hole tight, opposite hole next size up. Front Domino glued in).


    Regardless of which method, principle is elongated holes allow movement. The rabbet will have to be a bit deeper to do this.

    Might not work in your situation, but in the old days, furnituremakers often used nails in situations like this, knowing the nail will bend.

    A

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    Re: Assembly question.

    If you rabbet the horizontal piece instead of the vertical, the fasteners would be on the bottom. Then you wouldn't normally see them. But you would see a little end grain.

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    Re: Assembly question.

    Why all of the fuss about red cedar wood contraction/expansion in the design of this 33"l x 22" w piece with 4" w vertical pieces attached to the sides as shown in the OP's pic?

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    Re: Assembly question.

    Because I was originally planning on gluing the entire (crossgrain) joint and asked for opinions!

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