Flattening Warped Panels
#11
  
I'm making a blanket chest. I glued up the 3/4 cherry panels for the sides about four months ago. They've been sitting in a stickered stack in our heated basement since then. The chest box is about 38x18 by 16 high.

When I took them out of the clamps a couple of them rocked a little from corner to corner. I tried putting counter pressure with a caul under and clamps on the corners and it was pretty good when I had to let the project rest. Now I'm back at it and all of the panels have a bit of a rock to them. It's probably not too much once they're joined but I'm worried about cutting joinery.

The chest and plinth are to be box jointed. I had an awful time trying to make my own box joint jig and get good, square results so I bought an Incra box joint jig. Now after so much trouble I'm scared to death about cutting the box joints. Videos make it look so easy...

I searched for advice about flattening such panels but all I really found was plane or sand them flat, slice them up and reglue or tons of advice about how to avoid such a problem. Too late for any of those and I'm not sure I have enough wood if I wanted to reglue or plane (which I have no experience doing), plus not being convinced all that work would actually help.

Any wise advice on getting them flat enough I can cut the box joints accurately. I believe if I can get that worked out they'll assemble OK.
Phydeaux
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#12
  Re: Flattening Warped Panels by Phydeaux (I'm making a blanket...)
If your panels were flat after you first glued them up but now they aren't, then I think the moisture content in your lumber wasn't the same as the EMC of your shop.  If that's true, there ain't no fix but you might still be able to use the panels.  As you said, you could carefully sand or plane them flat, cut and reglue, etc. or you could go ahead and use them as is and hope for the best when you glue up the box.  

Assuming you go with the last option, you should be able to make the panels flat at one end by clamping it between heavy cauls, and then cut the joinery, probably by hand being the best option.  Then move the cauls/clamps to the other end and repeat.  


You might need to clamp both boards between cauls to get each joint together, too.  


John
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#13
  Re: Flattening Warped Panels by Phydeaux (I'm making a blanket...)
What about wetting the side which isn’t flat, allowing or causing it to straighten out while you mill the box joints?
Gary

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#14
  Re: Flattening Warped Panels by Phydeaux (I'm making a blanket...)
So the panels are warped. Twisted. There are only two ways a board can be warped or twisted. Clockwise or counter-clockwise. You can flip it over, spin it around, or flip it end for end and the twist will not change. (If you actually try doing this with a warped board you will have a better chance of understanding the next fact.) If you rip a warped board and re-glue it (in any configuration) the warp will never change. The best you can accomplish is limit the amount of surfacing by making each segment flat on one side before re-gluing. Sorry, but here's one more thing to consider. If your panels are all twisted the same way, the twist will be cumulative, not offsetting. All your box joints will fit fine but the box may not sit flat on the floor. You'll be pulling most of the twist out when the last corner goes together so it might not be too bad. Certainly not as bad as if your panels were out of square the same amount.
Sign at N.E. Vocational School Cabinetmaking Shop 1976, "Free knowledge given daily... Bring your own container"
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#15
  Re: Flattening Warped Panels by Phydeaux (I'm making a blanket...)
So here is what I would do regardless if was using box joints or dovetails. I would make a flat caul the length of the panel widths. Clamp it towards each end as I cut the joinery.

When you assemble the basic box, clamping everything down should square/flatten everything up.

It's always the trick to keep panels flat, but as long as you flatten each end with a caul while cutting the joinery, everything tends to come together fine. Done this many times.
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#16
  Re: Flattening Warped Panels by Phydeaux (I'm making a blanket...)
(05-04-2019, 03:08 PM)Phydeaux Wrote: I'm making a blanket chest. I glued up the 3/4 cherry panels for the sides about four months ago. They've been sitting in a stickered stack in our heated basement since then. The chest box is about 38x18 by 16 high.

When I took them out of the clamps a couple of them rocked a little from corner to corner. I tried putting counter pressure with a caul under and clamps on the corners and it was pretty good when I had to let the project rest. Now I'm back at it and all of the panels have a bit of a rock to them. It's probably not too much once they're joined but I'm worried about cutting joinery.

The chest and plinth are to be box jointed. I had an awful time trying to make my own box joint jig and get good, square results so I bought an Incra box joint jig. Now after so much trouble I'm scared to death about cutting the box joints. Videos make it look so easy...

I searched for advice about flattening such panels but all I really found was plane or sand them flat, slice them up and reglue or tons of advice about how to avoid such a problem. Too late for any of those and I'm not sure I have enough wood if I wanted to reglue or plane (which I have no experience doing), plus not being convinced all that work would actually help.

Any wise advice on getting them flat enough I can cut the box joints accurately. I believe if I can get that worked out they'll assemble OK.

Since you are making a chest, I assume these are large panels.  I made a dining room table. 18" wide panels x3.  After I glued them up I took them to a door manufacturer and he ran them through his triple belt sander to clean them up.  I had to stop the project for a week or so.  The panels warped/twisted.  This happened due to one side being exposed to the air and the other side not.  Unequal moisture content.  If air can't circulate around all the faces of the wood, it will cause this.  At least it was my experience.  Try stickering it again, with clamps and see if it flattens.
RP
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#17
  Re: Flattening Warped Panels by Phydeaux (I'm making a blanket...)
(05-04-2019, 03:08 PM)Phydeaux Wrote: ...I searched for advice about flattening such panels but all I really found was plane or sand them flat...
Any wise advice on getting them flat enough I can cut the box joints accurately...

Plane or sand them flat. And don't leave them sitting around for awhile after doing that.
Wood is good. 
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#18
  Re: RE: Flattening Warped Panels by ez-duzit ([quote='Phydeaux' pi...)
Clamping in a caul will work for a cup, but not a twist.

Regardless trying to use a twisted panel in a carcase is going to result in something out of whack.

I think the only solution here is to rip the panels apart and start over.
Everything is a prototype so its a one of a kind.
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#19
  Re: RE: Flattening Warped Panels by rwe2156 (Clamping in a caul w...)
If you clamp the boards flat between cauls as you cut the joinery, and if the joinery is strong enough to resist the forces caused by the warp (i.e. dovetails or box joints) you could be fine.  As mentioned above, a cup is removed locally by gluing a single joint, as long as both edges are straight.  A twist is harder to remove completely, but if you can get the 4th corner to close, it will be mostly taken out as well.
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#20
  Re: Flattening Warped Panels by Phydeaux (I'm making a blanket...)
I'm dealing with some cherry slab cabinet doors now. I have had to rip and joint, reglue one of the 8 already, and have one more that I need to redo.
When I do slab doors, I leave them thicker and wider for some time, giving me material to work with if I have to flatten them.
Steve





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