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Cupping on joined slabs

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  • #16

    Re: Cupping on joined slabs

    Originally posted by Egon View Post
    Dried 2x4's jointed and planed square&straight, covered with Saran Wrap and you will have cauls!
    Yes.
    But the OP never said if he clamped that way or not.
    He said his slab was resting on 2x4's ,never said how the slabs were glued up.
    • “The greatest lesson in life is to know that even fools are right sometimes.”Winston Churchill

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    • #17

      Re: Cupping on joined slabs

      Originally posted by redlee View Post

      Yes.
      But the OP never said if he clamped that way or not.
      He said his slab was resting on 2x4's ,never said how the slabs were glued up.
      Yes; quite correct.
      But did you not mention Cauls.
      ""I agree Rusty I donít use 2x4s for clamping the OP never said he was using them as such. I use cauls.""

      All I did was mention how to make cauls.
      Egon
      from
      The South Shore, Nova Scotia

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      • #18

        Re: Cupping on joined slabs

        I went back to read some of your earlier posts on the slab table to understand your situation a bit better.

        To review, you started out with 3" thick slabs, milled both top and bottom surfaces to leave about 2" thickness and glued the 2 slabs together, for a total table top width of about 40" to 45" (can't remember exactly). It's likely you are getting cupping from removing a third of the thickness and allowing any of the internal tension of the wood to relax further. Also, moisture content can still be at play, especially if you are heating your workspace, allowing the wood to dry further. If you can, get someone to make a MC reading on those slabs.

        Certainly try to flatten the slab as previously suggested by others, but you should also consider leaving it if it doesn't move much more. Having only 1/4" dip over 40 some inch span is not going to be noticeable on a table top. Your plates and cups will not fall off the table. I know this sounds like a bad suggestion, especially to a metalworker, where precision is ingrained in you. For jointery, precision is a must, but large flat surfaces, especially on slab work is rarely maintained even when initially made flat.
        Last edited by Kunzwerks; 02-13-2018, 11:25 AM.
        Measure twice, cut once ... and if that doesn't work try again

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        • #19

          Re: Cupping on joined slabs

          Originally posted by Egon View Post

          Yes; quite correct.
          But did you not mention Cauls.
          ""I agree Rusty I donít use 2x4s for clamping the OP never said he was using them as such. I use cauls.""

          All I did was mention how to make cauls.
          Not sure what you mean, yes I use Cauls but nowhere did I read where the OP used them.
          • “The greatest lesson in life is to know that even fools are right sometimes.”Winston Churchill

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          • #20

            Re: Cupping on joined slabs

            Someone may be misunderstanding my comment regarding clamping so for clarity; I am not talking about clamping while gluing. I'm talking about clamping AFTER THE GLUE UP AND AFTER IT HAS BEEN TAKEN OUT OF THE GLUE UP CLAMPS!! I would like to see the glued up slab clamped down to something like a flat table or bench top to KEEP IT FLAT!! In order to do that and at the same time have air movement for drying and stabilization above and below the slab I would also like to see the slab sitting on FLAT STICKERS not irregular 2x4's. Clear as mud huh?

            The reason I say this is because 2x4's are so wet generally, that they can twist out of shape over night.
            Antoni likes this.
            "Do it Right!"

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            • #21

              Re: Cupping on joined slabs

              Originally posted by Rusty View Post
              Someone may be misunderstanding my comment regarding clamping so for clarity; I am not talking about clamping while gluing. I'm talking about clamping AFTER THE GLUE UP AND AFTER IT HAS BEEN TAKEN OUT OF THE GLUE UP CLAMPS!! I would like to see the glued up slab clamped down to something like a flat table or bench top to KEEP IT FLAT!! In order to do that and at the same time have air movement for drying and stabilization above and below the slab I would also like to see the slab sitting on FLAT STICKERS not irregular 2x4's. Clear as mud huh?

              The reason I say this is because 2x4's are so wet generally, that they can twist out of shape over night.
              If your glue up is dry and the wood is dry and stable why would you clamp after the glue has dried?
              I have never used that method nor have I ever heard of it.
              Once a glue up is dry and you clamp it straight its going to go back to where it was before, wont it ?
              Wally in Calgary and Antoni like this.
              • “The greatest lesson in life is to know that even fools are right sometimes.”Winston Churchill

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              • #22

                Re: Cupping on joined slabs

                Originally posted by Rusty View Post
                1/2 of my point regarding the 2x4's is being missed. CLAMPS!!! The other 1/2 is the 2x4's. If the 2x4's are bowed or crooked in any way and you leave a slab sitting on them then the surface your project is sitting on is skewed before you walk away. Then you leave it unclamped to move wherever it wants. Maybe it won't move and warp at all but why do you want to risk it when all you have to do is put a couple of flat sticks under it and clamp it down. How can it hurt????

                Now you have a 1/4 inch problem. It's probably warped more while you're talking about it. If you think it can't, leave it alone over night.
                Thanks for the tip! Learning some valuable lessons here.

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                • #23

                  Re: Cupping on joined slabs

                  Originally posted by Kunzwerks View Post
                  I went back to read some of your earlier posts on the slab table to understand your situation a bit better.

                  To review, you started out with 3" thick slabs, milled both top and bottom surfaces to leave about 2" thickness and glued the 2 slabs together, for a total table top width of about 40" to 45" (can't remember exactly). It's likely you are getting cupping from removing a third of the thickness and allowing any of the internal tension of the wood to relax further. Also, moisture content can still be at play, especially if you are heating your workspace, allowing the wood to dry further. If you can, get someone to make a MC reading on those slabs.

                  Certainly try to flatten the slab as previously suggested by others, but you should also consider leaving it if it doesn't move much more. Having only 1/4" dip over 40 some inch span is not going to be noticeable on a table top. Your plates and cups will not fall off the table. I know this sounds like a bad suggestion, especially to a metalworker, where precision is ingrained in you. For jointery, precision is a must, but large flat surfaces, especially on slab work is rarely maintained even when initially made flat.
                  The wood is around 10%MC according to my cheap little LV Moisture meter. Wouldnt the cupping be more likley from having one side flat on the workbench and heating up the top side with a heat gun and leaving it like that over night? It has been joined for over a week in my garage where the temperature is controlled ( I did turn it up a few degrees when i did the epoxy) and checked it for flat a couple days before the epoxy because I have been paranoid about it moving and it was dead flat....

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                  • #24

                    Re: Cupping on joined slabs

                    I got the slabs at 12% MC kiln dried and they have been in my garage for about 4 months

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                    • #25

                      Re: Cupping on joined slabs

                      If you garage is not climate controlled such as the inside of your home, then what you did by laying one side of your slab flat on your work bench is what caused your problem. Here on the west coast we can have days that vary in humidity from one day to the next, the side of your slab up against the bench was not able to either absorb or displace moisture at the same rate as the opposing slab face that was more exposed to the air.

                      You can try placing the slab on your bench top with stickers between it and the bench and just let it sit there for a few more days without clamping it down. It may well move back to closer to flat all on its own.

                      Iíve built a number of slab tables and they all move with changes in humidity, and this is with them being in the home. Wood is alive and when dealing with thick slabs itís just one aspect youíll need to learn to live with.
                      Kunzwerks and Rusty like this.

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                      • #26

                        Re: Cupping on joined slabs

                        Originally posted by redlee View Post

                        If your glue up is dry and the wood is dry and stable why would you clamp after the glue has dried?
                        I have never used that method nor have I ever heard of it.
                        Once a glue up is dry and you clamp it straight its going to go back to where it was before, wont it ?
                        In order:

                        1....Rich, Why not do it? It can't hurt and in this case NOT doing it is hurting! We live in Alberta and may not have the issues some face in other areas of Canada. I'm from Ontario and I've seen incredible movement in wood. I had a picture years ago of a 14 foot 2x4 that twisted 180 degrees over a weekend. I used to nail lifts of 2x4's together if I had to leave them on site for any length of time.

                        2....Although you've never used it you've heard of it now.

                        3....No why should it? If it was straight to start with and a guy has to assume it was, why would clamping it do it any harm? The clamping sure as hell won't twist it.

                        The peanut gallery showed up I see.. and I don't mean you Rich! Now if we could only have the peanut gallery, or anyone else for that matter, please tell me why the clamps will cause a problem I will gladly listen and I bet the OP will too!

                        Now let's go to post #24 where we learn a little more about what has been done. Is there anyone else here who thinks just maybe a 40 inch wide slab laying on a flat surface will hold ANY MOISTURE THAT'S PRESENT ON THE BOTTOM OF THE SLAB while someone works on the top of that slab with a heat gun DRYING OUT THE TOP AND NOT THE BOTTOM, might just possibly warp the wood slab upwards? OR,,,,,, am I the only one. Just asking!!

                        Nice one John, See #25. I think you agree with me.
                        Last edited by Rusty; 02-13-2018, 11:59 PM.
                        "Do it Right!"

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                        • #27

                          Re: Cupping on joined slabs

                          Originally posted by redlee View Post

                          Not sure what you mean, yes I use Cauls but nowhere did I read where the OP used them.
                          You mentioned Cauls. The OP was talking about 2x4's. I mentioned how the 2x4's could be converted to cauls.

                          Nowhere did I read about the OP mentioning Cauls.



                          Egon
                          from
                          The South Shore, Nova Scotia

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                          • #28

                            Re: Cupping on joined slabs

                            I forgot about a lot of the woodworking theory now as i am "set in my ways" from doing the same thing over and over 5 days a week for close to 30 years.
                            But ! Isn't 12% MC kiln dried WET ? and measured where ? On the surface of such a thick slab won't do it ? Excuse me but my guess is this glue up of 2 boards totalling 40" will never stay in one position for long. Happy V Day guys.
                            Les Groeller likes this.

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                            • #29

                              Re: Cupping on joined slabs

                              Originally posted by RV Sam View Post
                              I forgot about a lot of the woodworking theory now as i am "set in my ways" from doing the same thing over and over 5 days a week for close to 30 years.
                              But ! Isn't 12% MC kiln dried WET ? and measured where ? On the surface of such a thick slab won't do it ? Excuse me but my guess is this glue up of 2 boards totalling 40" will never stay in one position for long. Happy V Day guys.
                              12% MC is wet?? measured from a bunch of different spots on the boards, how else would you measure?

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                              • #30

                                Re: Cupping on joined slabs

                                Originally posted by Antoni View Post

                                12% MC is wet?? measured from a bunch of different spots on the boards, how else would you measure?
                                Not sure as everything i have purchased is pinned before delivery on dif boards in the lifts. If i remember correctly kiln dried lumber for cabinet work is down around 8% ???????? AND that is in the centre of the board, not the surface or a few 16ths in.
                                The wood needs to be killed and i 'm not sure if 12% will do that . Just tossing out a "possible" cause for ya !
                                Good luck.

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