Steel insert in tabletop to avoid warping and twisting. - Woodworking Talk - Woodworkers Forum
 
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post #1 of 7 Old 01-16-2018, 07:40 AM Thread Starter
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Steel insert in tabletop to avoid warping and twisting.

Hello this is my first post, and I am very new to furnituremaking but I have built houses for some years.

I have a question:

I have a pine tabletop glued together of 4 boards. The table top is 89cm x 210cm. The thickness is 6,5cm.

The style of the table is rough and rustic. I want it to look old but straight. I am concerned that it will warp and twist over time so i thought: What will happen if I cut a groove on the backside of the tabletops width and put in a steel reinforcement "bar" which is 2cm thick and 5cm wide? Like a stretcher. I want to glue it in place and maby put in some screws.

What will happen when the table is moving cause of temperature and air moisture?

If the table cracks tiny it doesn't matter cause of the style of the table but if it cracks big cracks and gets ruined its no fun.

Sorry about my bad english.

Last edited by tobiassen; 01-16-2018 at 07:49 AM. Reason: type error
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post #2 of 7 Old 01-16-2018, 07:58 AM
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Take the opportunity to read some of the recent posts on tabletops, you will get a good idea of what can happen. Proper design will not need steel, but by itself steel bars on the undersides mounted correctly will do the job, depending on how the top is joined to the rest of the table. Slotted holes are the key.
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post #3 of 7 Old 01-16-2018, 08:08 AM
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You would have to be careful putting a piece of steel in the top. The holes to screw the steel to the top you would have to elongate the holes to allow for the wood to shrink and not completely tighten the screws. Wood expands and contracts and if you don't let it you can cause the top to split. As thick as the top is that you are making I don't think I would worry about it. Just put a finish on both sides of the top and I think you will be alright. As thick as the top is if it decided to warp it would just bend the steel.

When you make a top like that if you would select wood that was more toward the center of the tree it would help prevent warpage. You can see this by looking at the end grain. This wood the annual rings in the end grain are nearly perpendicular to the face. Then when you glue it together you alternate the direction of the end grain as much as you can.
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post #4 of 7 Old 01-16-2018, 02:46 PM Thread Starter
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Thank you for answers. So the thicker the tabletop, the less the risk of warping/twisting?

Im thinking of making a "floating" stretcher of steel under it. Fastened with screws that has playroom in the holes of the steel stretcher.
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post #5 of 7 Old 01-16-2018, 03:17 PM
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Quote:
Originally Posted by tobiassen View Post
Thank you for answers. So the thicker the tabletop, the less the risk of warping/twisting?

Im thinking of making a "floating" stretcher of steel under it. Fastened with screws that has playroom in the holes of the steel stretcher.
The wood itself has the final word but generally the thicker table top you make does lessens the chance of warp.
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post #6 of 7 Old 01-16-2018, 04:09 PM
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It's always about the physics ...

No matter what part of woodworking you are discussing, whether building a project,or using machines or hand tools, physics plays an ever present and important role. In the case of a table top, and "warping" issues, use this as an example. Take a piece of cardboard about 6" x 12" and lay it on a flat surface. This is your ideal table top, supported all around and unable to flex. Now pick it up and twist it by hold one short edge and rotating the opposite edge. It will flex completely as much as 1" in that 12" length. Now if you glue a 1" wide perimeter border at 90 degrees on all four edges, like the open half of a box and try to flex it. you find it will hardly move at all. The wider/higher the border frame is, the stiffer the cardboard will become.

This is what happens when you add aprons around the perimeter of a table top. The aprons are typically set in from the edges so they don't show or bump your legs. Whether the aprons are steel or wood they will stiffen the top, steel being stronger inch for inch than the wood.

If a design is contemporary then steel can be used, but in a traditional design steel would not be suited and has not been used for centuries. The joinery in an all wood top provides the strength as does the arrangement and stiffness of the members. The greater the depth of the section, say 12" vs 6" the less resistant to breaking or deflection AND the species of wood, Oak vs alder or Pine has some effect, but the design itself plays a very important role. Triangles resist movement, rectangles do not and will collapse without bracing... it's that simple.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 01-16-2018 at 04:54 PM.
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post #7 of 7 Old 01-17-2018, 12:47 AM
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Get a design together an post it here with questions...More can be (perhaps) offered then in the way of guidance. Metal can work in some designs, yet is often more a "placebo" than a reality, as wood can bend metal too...Even heavy metal...and there is the issue of staining as well in some species...

This current post thread: 10 Foot Long Dining Table Design Question has a pretty good depth of viewpoints on the subject, as just one example...

Good luck,

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