Alonzo

How do I stop this cedar slab from cupping in one corner

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I have this cedar slab that's bending up in the right corner as seen in the picture. Its been in my shed for the past several months and feels very dry. What can I do to flatten out the top without planning it. Would kerf cuts in the bottom help relax it so it lays flat? I'm attaching it to 1/2" square steel legs. Any advice?

How do I attach a photo? Every time I try, the upload fails. The file type is correct, jpg. 

0917171714a.jpg

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8 minutes ago, C Shaffer said:

I'd be tempted to find a line down the middle to rip joint and re-glue. You are fighting the log center. 

Yup those cracks are right along the pith. 

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18 minutes ago, C Shaffer said:

I'd be tempted to find a line down the middle to rip joint and re-glue. You are fighting the log center. 

I've read that the pith is kind of like a cavity in a good tooth but don't understand all I know about it. Would op be advised to not only rip down the center of it but to also move over a tad on the two pieces and remove some of each prior to regluing the two pieces together? 

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I think the pith has been removed in this board. Pith or no, the problem is the short arc center grain. As it shrinks along the width, it will draw the "wings" up. Hopefully that will be minimal going forward as I assume the slab is now dry. Paging @Eric.

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Yeah pith is almost always unstable, and will remain unstable in perpetuity.  Your only real options are to mill that board flat and hope that it doesn't move again...which means you will lose a ton of thickness due to the severity of the cup...and still not be assured that it won't continue to move; or do what the guys suggested, and rip the pith out and glue the two halves back together.  You'll lose 2-3" of width.  Fighting pith is a losing battle, unfortunately.  The rest of your board looks to be mostly riftsawn and quatersawn (which is usually the case when you have the center slab that contains the pith), so once it's removed it should be a very stable slab...assuming it's fully dried.

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Then' there's the issue with the remainder of the butterfly. You could always remove the whole center portion and replace it with a walnut racing stripe? Just kidding

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Its only the right corner that's bending up, so if I rip the entire thing down the middle, the remaining 3/4 of the table won't line up properly. The rest of the slab is flat. Its only about a 2'x2' section curling up. This slab is just above the pith.

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It looks like that knot is part of the problem. If it were in my shop I'd still rip it in half and hope to get lucky and relieve some stress.

Joint that slab back together use some cauls to hold it flat in the clamps.

This is one of those times were a accurate jointer with long beds comes in handy

Nice looking slab.

Aj

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I think what you are calling a knot is the center of the log. I also don't see a corner warp. The plank lifts from the center like the dihedral shape of turkey vulture flight. I think maybe what you are trying to communicate is that the other end of the board is still flat? I hope you find a solution, but it seems we have not yet communicated clearly. 

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Right, it's not a knot, it's the center of the tree, which is called the pith.  The pith is always unstable and until you remove it, you'll likely continue to have flatness issues with that board.  Best case scenario, it will continue to crack along the pith.  If you see pith on one end but not the other, it's because the slab was cut tangentially through the log.  It may seem like a waste to you to remove 3" of material from the center of the slab...but the alternative is worse.

You'll need to rip the slab in half, remove the pith section, joint the two boards back to flat, the glue the two halves back together.  Otherwise you're kind of stuck with a warped board.

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I think it's both, pith and knot. 

Rip the pith out and re-glue, that will fix one of the problems. Not sure you can do anything with the hook on the tip of the slab. 

 

-Ace-

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This piece of sycamore I bought is another example of a slab that was cut from the center of a log.  Not a great pic but if you look closely you can see that it's almost entirely riftsawn and quarter sawn, except for the center which is entirely pith...where all the cracks are.  I don't intend to use this piece in slab form...rather, I'll be cutting it into chunks and resawing it for whatever project it becomes...so the pith doesn't bother me.  But if I were looking for a slab to use in its entirety, I would have passed altogether on this piece due to the pith, despite how cool the rest of the slab is.  Pith is no good.  It's as useful to a woodworker as a banana peel is to a smoothie.

 

KdYfAs3.jpg

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I agree ripping out the pith would help significantly, but I'll add a possible alternative that you could try. You could fasten several cleats to the underside and pull it flat with a series of screws in slotted holes. If that works, then you might avoid the ripping and re-gluing. If it didn't work, then you could still rip it and re glue it. The advantage of the cleats is that they may hold it flat indefinitely.  Just don't screw through the top surface....

 

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On 9/17/2017 at 10:43 PM, Alonzo said:

Its only the right corner that's bending up, so if I rip the entire thing down the middle, the remaining 3/4 of the table won't line up properly. The rest of the slab is flat. Its only about a 2'x2' section curling up. This slab is just above the pith.

I'd be considering a 2x4 glued & screwed down (behind the metal, so it won't be seen)to make it flat then attach  it to metal.

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It must not be completely dry.  To the touch means little to nothing.  You probably won't know how much it will move until after going through a heating season in the house.  I'd wait until after that to figure out what to do with it.

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