Help and advice on warping large panels


deav

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After rolling this around in my head a little longer and studying the picture of the finished piece. Notice the crack is next to the board that contains the most sapwood on either side. Sapwood expands and contracts considerably  more than heartwood.

 

So you may want to remove as much of the sapwood as you can. Every little bit helps. 

 

 

 

-Ace- 

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Technically it's cupping, not bowing.

 

Yea, I know...I only used bow because he said "I don't think my client will want a situation where they may bow 2" off the wall, in the middle."   It's definitely a cupping of the panel in this case...but regardless, he can hold the panel flat preventing any cupping and still allow it to expand/contract.  He was saying he wants to add even more steel and stuff and try to actually prevent all movement because he didn't want the curvature, and I just wanted to point out "wood movement" does not have to mean becoming non-flat.

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What about taking u shaped steel stock with an interior dimension the same as the thickness of your wood and capture the entire panel along the end grain on each side. Cut slots in the steel everywhere except the center for screws. Then attach one or two cleats to the steel to hang the piece. It will be able to expand and contract with humidity but not cup and it will hang on the wall very securely.

If you don't like the idea of the steel showing on the front you could do the same with simple angle iron on the back and end grain.

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I could be entirely off base, but the whole pocket hole screws on one side lends me to think it can also aid or be a big part of this problem? Wouldn't that essentially pull the back of the panel tight impeding even movement. I've never seen or heard of anyone using that technique for a panel glue up.

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What about taking u shaped steel stock with an interior dimension the same as the thickness of your wood and capture the entire panel along the end grain on each side. Cut slots in the steel everywhere except the center for screws. Then attach one or two cleats to the steel to hang the piece. It will be able to expand and contract with humidity but not cup and it will hang on the wall very securely.

If you don't like the idea of the steel showing on the front you could do the same with simple angle iron on the back and end grain.

 

Smart idea, thanks.  I will explore this.

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I don't know that they are hurting, but they certainly aren't helping. A long grain glue joint is as strong as it gets.

 

Yeah, I don't know if they're helping or hurting.  If they have a pull on the back I suppose it could counteract the pull on the front from the resin.

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This whole thing has been so over-complicated.  Breadboards.  Problem solved.

Breadboards are only a temporary solution to a permanent problem even with them it will likely crack. The epoxy tracks are binding the face. Epoxy does not expand and contract. There is no much epoxy routed into the face across the grain its going to hold tight.

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You are right, but battens properly fastened should also solve the problem. Aesthetically that would be my choice. But yes, it has been over complicated.

Battens dont stop movement they just keep the surface flat. The epoxy stops the movement battens will only serve as a temporary solution until the face cracks.

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I don't know that it's over complicated.  It's complicated because of the panel size and introduction of resin.

 

It sounds like some of you are saying this is a problem without a solution, so long as I'm epoxying the front.

 

 

Client is suggesting a full 3/4" plywood backer, glued and screwed.  If the epoxied artwork is fully glued and screwed to a plywood backer, what do you think will happen to the face?  Ply cracks with walnut?

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I think the only real solution is veneer. You can start off on the thick side. Do your epoxy inlay the take it down to about 3/32 or so on the wide belt. I don't know how your equipped so hard to give a solution.

I tried a veneer test piece today with a vinyl mask applied before routing to keep the resin from seeping into the veneer. My goal is for a flush finish. That's why with the solid stock I can over pour and sand excess away. With veneer it's too easy to sand the veneer away. And if I underpour its not a flush finish. I want veneer to work but I really don't think I can make it work.

I think perhaps the best approach is a combination of everyone's suggestions:

-quarter sawn stock

-narrow boards, 3-5"

-nix the pocket screws

-reduce number of screws for bracing and slot steel

-employ some sort of bread board or angle iron version of that.

I have another idea that id like to run by you guys:

My local hardwood supplier has thin walnut stock. I think they're calling it backer board, but I'm not sure. It's basically solid walnut that is about 3/8" thick. My thought is to make my own "veneered" ply by first joining a panel of this thinner stock and then gluing that to a sheet of ply. It's about half the width of the 4/4 stock I'm using. Then routing this new panel and going about my resin process in the same way. Same song different verse, or could this work?

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Can you answer for us how you are sanding? If you are using a wide belt, then you and Don are just missing each other by a hair. Start with 3/8" material over a stable substrate. Rout it deeply. Pour your resin. Then sand the whole face down to veneer thickness. You could carefully frame the piece for the appearance of solid timber. If you don't have a wide belt, it could be wise to contract someone to sand the finished piece for you. Shop time and some sanding media could not hurt your bottom line that badly.

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Can you answer for us how you are sanding? If you are using a wide belt, then you and Don are just missing each other by a hair. Start with 3/8" material over a stable substrate. Rout it deeply. Pour your resin. Then sand the whole face down to veneer thickness. You could carefully frame the piece for the appearance of solid timber. If you don't have a wide belt, it could be wise to contract someone to sand the finished piece for you. Shop time and some sanding media could not hurt your bottom line that badly.

I'm using an edger for sanding away excess resin. The type used for edge work on hardwood flooring.

I do understand your point and it makes sense. I guess what I'm realizing is perhaps I can use my same 4/4 stock, rip it down to 4" wide, turn it 90 degrees and rip each 4" wide 4/4 stock into three veneer strips that are about 1/4" thick. Glue those to ply and go about my normal process, and not have to sand away so much material.

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Even1/4" solid stock glued to ply will still try to cup unless you glue the same to both sides, back side can be ugly but balanced construction is needed.

I had to re make a 4ft round tabletop( built by someone else) that was 4/4 solid wood on top of ply. The wood moved the ply didn't , 2" cup in the center of a 4 ft circle! I made the new top from 5/4 stock with 2 batten strips and slotted for the screws. I wax the face of the strip to the underside of the table to stop any sticking.

Maybe you could figure out a way to have a slight open seam in the resin at each wood seam ?

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