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Thread: Butt joint for wooden worktop

  1. #1

    Butt joint for wooden worktop

    I'm installing a solid wood kitchen worktop on a U-shaped set of cabinets. I know I'll need to allow for movement in the wood, so shouldn't mitre the joints. I understand I ought to use worktop bolts routed into the underside to get a good join. I'm also concerned about alignment, especially since I can't clamp on top and bottom to get them to line up, and in other circumstances I'd use dowels to ensure the pieces line up well. Will dowels prevent the wood from expanding and contracting as necessary? Does anyone with experience with solid kitchen countertops have any advice? Many thanks in advance for any help you might have.

  2. #2
    I use biscuits in combination with T bolts. You can glue them in with silicone or rubber cement if you want a flexible joint. A butt joint that ends with a small miter looks nice.

    Screen Shot 2024-06-14 at 4.52.55 PM.png
    Last edited by Maurice Mcmurry; 06-14-2024 at 5:59 PM.

  3. #3
    That's helpful, thanks! I was considering a hockey-stick style joint with a short mitre -- I'd definitely use it if the edges of the worktop were rounded over, of course, but it would look smart in this case too. Do the biscuits allow for more movement than a dowel would?-- or am I worrying about nothing?

  4. #4
    Yes. Biscuits do not have the abrupt 90 degree interface that dowels have. You can also cut them a little sloppy and use no glue at all. A domino would be similar if the mortis is cut a little wide.

    Your worries are well founded. You want the joint to work like a bread board end.
    Last edited by Maurice Mcmurry; 06-14-2024 at 6:51 PM. Reason: P.S.

  5. #5
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    Iím absolutely certain your worried about nothing. The bolts your going to use with will allow for adjustments to flush the top. Just donít tighten them all the way until you have your pieces alignment just the way you want it.
    Once their tight they donít move unless have a cartoonishly large hammer.
    I never needed or used the biskets on prefabricated counters Iíve installed.
    Good Luck
    Aj

  6. #6
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    Wouldn't the countertop, if mitered, expand at the same rate on both sides of the miter? Don't know why it wouldn't...

    I've used some zip bolts to join miters on a cabinet I am making for my daughter. They work great and align the material well. You can buy them from Knapp (butt joint connectors) or Lee Valley (miter and butt joint connectors...).

    https://www.leevalley.com/en-us/sear...erOfResults=25

  7. #7
    A miter should work fine too. I have not done a miter with wood counters. There are lots of images on the web of mitered wood counters. A counter top shop should be able to cut the miter and T bolt pockets on the same rig that does post form formica and particle board counter tops (with a little tweaking).

  8. #8
    You definitely should be concerned with seasonal movement on a wide solid wood butt joint. You can look up the values depending on width, species, grain orientation and expected change in moisture content at the wood shrinkage calculator at Woodweb.com. For example, a 24" wide flatsawn sugar maple top is predicted to move 11/32" with a change in moisture content from 6-10%. I typically use splines or dominos in oversize mortises to keep the surfaces flush and zipbolts to keep the joints together. If you use biscuits make the pockets deep enough to allow for the expected sideways movement. Don't glue the butt joint except at one end or in the middle.

    If you use a jack miter at the inside corners be sure to glue the joints there and expect the outside corners to not remain flush, as with breadboard ends. You can hide the movement under backsplashes, but if the outside corners need to remain flush then stay away from jack miters and let the inside corners float. If you use a full mitered joint the bolts should hold the joint together but it will drift out of square, >90* in the wet season and <90* in the winter. Allow for movement when you fasten the tops to the cabinets.
    Last edited by Kevin Jenness; 06-14-2024 at 8:00 PM.

  9. #9
    Quote Originally Posted by Mike King View Post
    Wouldn't the countertop, if mitered, expand at the same rate on both sides of the miter? Don't know why it wouldn't...

    I've used some zip bolts to join miters on a cabinet I am making for my daughter. They work great and align the material well. You can buy them from Knapp (butt joint connectors) or Lee Valley (miter and butt joint connectors...).

    https://www.leevalley.com/en-us/sear...erOfResults=25


    Yes, both sides would expand and contract roughly the same, doubling the gap at the inside and outside of the miter when drier and wetter respectively.

  10. #10
    Quote Originally Posted by Cameron Wood View Post
    Yes, both sides would expand and contract roughly the same, doubling the gap at the inside and outside of the miter when drier and wetter respectively.
    That would be true if the parts were fixed at 90 degrees. If the miter were bolted together and the legs allowed to move above the cabinets the angle would change. If the legs were fastened rigidly to the cabinets and the miter bolted together splits and checks would likely develop over time in the top, or the fasteners connecting the top and cabinets would fail.

  11. #11
    My wood counters do not change seasonally in any perceivable way. They have consistently shrunken. They are now 24 11/16" wide. When they were constructed from kiln dried wood 14 years ago they were 25 inches. Think about a mitered 2x6 deck rail. I have those perfect when I built a new deck. A month later they are wide open at the inside corner.

  12. #12
    Quote Originally Posted by Maurice Mcmurry View Post
    My wood counters do not change seasonally in any perceivable way. They have consistently shrunken. They are now 24 11/16" wide. When they were constructed from kiln dried wood 14 years ago they were 25 inches. Think about a mitered 2x6 deck rail. I have those perfect when I built a new deck. A month later they are wide open at the inside corner.
    If there was a 45˚miter in your countertop, the gap on the inside would be 7/16". (except in the cases of Kevin Jenness' variations above)
    Last edited by Cameron Wood; 06-15-2024 at 12:45 PM.

  13. #13
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    Ok, I get what you are saying about opening at the inside of the miter. But a butt joint will also have a problem. If the counter is pinned to the inside of the u, then the counters will pull away from the wall. If the counter is pinned to the outside of the u, a gap will appear in the joints.

    It might be better to not use solid wood countertops.

    Mike

  14. #14
    Quote Originally Posted by Mike King View Post
    Ok, I get what you are saying about opening at the inside of the miter. But a butt joint will also have a problem. If the counter is pinned to the inside of the u, then the counters will pull away from the wall. If the counter is pinned to the outside of the u, a gap will appear in the joints.

    It might be better to not use solid wood countertops.

    Mike
    In some cases movement can be concealed under a backsplash. I have an L-shaped desktop with the legs pinned at the back (no backsplash) and eased edges at the butt joint to match the front edges and disguise the seasonal movement along the joint line. The butt joint does not show a gap. The top is Honduras mahogany so pretty stable but the detail will work with other woods. I have also made countertops with 3/32" shopsawn veneer where solid wood movement was not acceptable.

  15. #15
    Quote Originally Posted by Cameron Wood View Post
    If there was a 45˚miter in your countertop, the gap on the inside would be 7/16". (except in the cases of Kevin Jenness' variations above)
    Someone should do the math for the wall gap that would appear at the end of two 8 foot arms of a mitered L if both halves shrink 5/16. I would have to lay it out full size. I am trying to imagine what becomes of the 45 degree miter? It turns into a 44.75?

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