plank tabletop bowing?? - Woodworking Talk - Woodworkers Forum
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post #1 of 30 Old 03-17-2014, 05:08 PM Thread Starter
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plank tabletop bowing??

hi all and thanks in advance for helping out a newbie.

i've recently constructed a dining table, photos attached, the top of which was made by joining a few home depot 2x8's edge to edge using wood glue, pipe clamps, and pocket screws. the table top was original fairly flat, and fit onto the pedestals fairly well. since then, one end of the table has bowed quite a bit. my question to you is: what do you think is causing it to bow, and how might i avoid similar results in future projects (i.e. where this type of bowing may actually be a problem). luckily, the bowing doesn't render the table useless...

thanks again!
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post #2 of 30 Old 03-17-2014, 05:22 PM
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Construction grade lumber is not dry enough for furniture making. It needs to be dried further. Solid wood tops also need to be attached in a way that allows for movement or they will split/crack/etc. Your boards are loosing moisture unevenly and are cupping as you see in your photos.

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post #3 of 30 Old 03-17-2014, 06:23 PM
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I can't see in the pictures. Is the underside of the top finished. If it is not finished or has a very thin finish that could cause the top to warp as it would let more moisture get to the back causing an emballance in the moisture content. What it needed more than anything is more 2x4's running cross the table on the underside. Normally a table has a skirt for this purpose.

I think the bow could be fixed. I would probably cut a board on a curve and clamp it to the top when you are not using it and force the top to bow a little the opposite direction. Let it sit for a few weeks and then put some more cleats on the underside.
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post #4 of 30 Old 03-17-2014, 07:11 PM
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Originally Posted by mdntrdr View Post
Construction grade lumber is not dry enough for furniture making. It needs to be dried further. Solid wood tops also need to be attached in a way that allows for movement or they will split/crack/etc. Your boards are loosing moisture unevenly and are cupping as you see in your photos.
+1

I agree 100%

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post #5 of 30 Old 03-18-2014, 11:07 AM Thread Starter
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thanks

thanks very much for taking the time to reply.

the underside of the tabletop is indeed *not* finished the same as the topside. The topside has three coats of stain and two coats of poly; the underside has just one coat of stain and that's it. so it makes sense that the wood is "curing" unevenly topside vs underside. I guess i got a little impatient with the finishing process...and also just really needed a dining table already (:

i'm just a step above amateur in terms of woodworking, so learning as i go... i used home depot lumber because it's economical, and will probably continue to use it for the same reason. can you offer me any tips on what to do differently in my next projects? obviously finishing all faces of the wood equally is a good start...
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post #6 of 30 Old 03-18-2014, 11:39 AM
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Quote:
Originally Posted by fish02906 View Post
i'm just a step above amateur in terms of woodworking, so learning as i go... i used home depot lumber because it's economical, and will probably continue to use it for the same reason. can you offer me any tips on what to do differently in my next projects? obviously finishing all faces of the wood equally is a good start...

Let it dry. Get the straightest wood you can find (if you search enough, there usually is some!), bring it home, stack it with spacers between the layers, put some weights on the top to keep it reasonably flat, and let it sit for a month or two. Ideally, you'd let it sit in the space it will be set in at the end, but most of us don't want to have stacks of wood in the dining room for months a time, so put it where you can. If you can put it somewhere where the temperature and humidity are the same as they are in the final location, you'll be in good shape.

At the end of that time, all the boards will have warped. Some will bow, some will twist, some will cup, and a special few will do all three. I recommend buying more than you need so you can throw those few away. Some amount of bow can be ignored, depending on what you're building, as can some amount of cup. There are ways to work around them, and you'll learn them all if you keep working with Home Depot wood. Any significant twist needs to be planed out, which is a nuisance, so I usually don't bother.
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post #7 of 30 Old 03-18-2014, 01:48 PM Thread Starter
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wow. sounds like i'm buying the wrong wood, huh.
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post #8 of 30 Old 03-18-2014, 03:59 PM
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Solid wood tops also need to be attached in a way that allows for movement or they will split/crack/etc.
whats the best way to do that?
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post #9 of 30 Old 03-18-2014, 04:12 PM
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All in all, it looks very nice.
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post #10 of 30 Old 03-18-2014, 04:48 PM
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whats the best way to do that?

For the example the OP showed, I would attach using fender washers and fasteners through elongated holes through the horizontals into the top. I would just snug the fasteners so the top can expand and contract with seasonal movement.

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post #11 of 30 Old 03-18-2014, 05:23 PM
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wow. sounds like i'm buying the wrong wood, huh.
I've made a bunch of table tops out of 2x4's and didn't have a problem with warpage. I ran all my wood over a jointer and straightened the joints but I always made a skirt for the table out of 2x4's as well to hold the top flat. I'm sure there is the potential of getting some pretty green lumber but you can usually tell by the weight and I avoided any board which seem heavy. For the most part I avoided a heavy board because of the sap contend having it leach sap through the finish.
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post #12 of 30 Old 03-27-2014, 10:52 PM
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It has very little to do with uneven drying or uneven finishing. This is a recurrent topic of concern here so we need to understand the main facts.
Wood warps as it dries if the growth rings are not flat.
Wood shrinks almost twice as much tangentially as it does radially. If you wood has not dried to the final moisture content where it ends up, it will warp.
Construction wood is especially bad as it is often cut from fairly small trees so the board has prominent tight growth rings (small radius). If you look at the table there are almost certainly tight rings in the most warped boards.
If you can find the boards cut thru the centre of the tree and cut out the centre you will have quarter or radially cut wood that is the most resistant to warp.
Letting it dry to the final inside moisture content (for inside furniture) is vital. Avoid board just off but near the centre. Furniture logs usually have a 4x4 inch centre of the tree left out or cut out later.
Once dried you can joint out the warp and plane the board to flat. Only if the humidity does not change will it stay flat.
If you put all the rings the same at glue up, the warp will be in one direction over the top and it can be held flat with cleats in holes that allow movement. Some like to alternate and live with the wavy board.
There are good essays on the topic I n places like Wikipedia under wood movement with drying.
Hoping to help
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post #13 of 30 Old 03-28-2014, 08:58 AM
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It has very little to do with uneven drying or uneven finishing.
i repsectfully disagree with this statement. picture proof - warpage is "up" on all boards, even though (some) growth rings are alternating, as best i can tell in pticture.

i have always experienced warping, even on plywood and mdf, if one side is finished to a different level than the other side.
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post #14 of 30 Old 03-28-2014, 09:43 AM
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Originally Posted by fish02906 View Post
..... one end of the table has bowed quite a bit. my question to you is: .... and how might i avoid similar results in future projects ...
Quit buying your lumber at Home Depot.
Calling Home Depot the K-Mart of lumber would be a compliment.

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post #15 of 30 Old 03-28-2014, 10:58 AM
where's my table saw?
 
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I made a door from 2 x 8 planks here

You may learn something from this door build, in which I used 2" X 8" pressure treated planks which had air dried for several years:

http://www.woodworkingtalk.com/f2/do...1-4-ply-55717/

I doubt you will find a single straight, flat, uncupped 2" X (anything) from Home Depot after leaving it out in the warm shop. Even house framers rush to use the construction grade lumber and get it secured along with the other lumber in walls and floors as soon as possible.

I always "line of sight" a 2 X board (milled lumber) or a plank (unmilled rough sawn) before I purchase it or attempt any milling operations myself. I sometimes forget to distinguish between boards and planks as in the link above. I sight along the length of the boards for curves and twists, cups are more easily spotted.

Always apply a sealer to both side of any workpiece to prevent uneven drying. This will "minimize", but not prevent any internal twisting due in part, from where the plank was sawn on the log. If you look at the end grain and find large sweeping arcs, that board may cup as it dries.. If the end grain is all vertical, as in quartersawn, it will cup far less, if at all.

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; 03-28-2014 at 11:12 AM.
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post #16 of 30 Old 03-29-2014, 10:16 AM
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i repsectfully disagree with this statement. picture proof - warpage is "up" on all boards, even though (some) growth rings are alternating, as best i can tell in pticture.

i have always experienced warping, even on plywood and mdf, if one side is finished to a different level than the other side.
You have missed the point. The statements are accurate. When wood dries it warps to straighten out the growth rings.!!! The issue of tangential to radial is vital.
Or course there are other circumstances to temporarily warp boards but we should be talking about boards at equilibrium with the surroundings.
Wetting one side or unevenly drying the two sides will warp boards but that is NOT the issue here.
Butting different finish on the sides will cause a temporary shift as one side equilibrated more quickly.
Plywood has some different characteristics. Wetting or uneven moisture content of the two sides will warp away from the most damp side.
Read it again!!!
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post #17 of 30 Old 03-29-2014, 11:35 AM Thread Starter
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Quit buying your lumber at Home Depot.
Calling Home Depot the K-Mart of lumber would be a compliment.
Where do you recommend i buy wood for my little home projects? recall i'm not a "pro"...i mostly just do this for my own entertainment. that dining table is the only "furniture" i've ever put together.
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post #18 of 30 Old 03-29-2014, 11:39 AM Thread Starter
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cleats in holes that allow movement.
Could you please post a photo or a link to a photo showing what appropriate/proper cleats look like?? would be very helpful. thanks!

to reply to some other comments; in the attached photo i try to show you the end grain on the pieces i used. notice that the left-most piece is the only piece with upward curves, which the other pieces are all down-ward. i admit i did not pay attention to this when putting them together. is there a rule of thumb when joining boards edge to edge in this fashion?

thanks to everyone for commenting. i find all your comments pretty helpful and enlightening, and i'm sure i'm not the only one.
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post #19 of 30 Old 03-29-2014, 01:15 PM
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The cross planks at the top of your trestle table legs would classify as cleats.
A common table has an apron and the end boards that run perpendicular to the board grain direction become the cleats. A cleat could be the board cross joining a solid wood door where they hold the boards together and keep the door flat. If the boards are separate(not glued together) , cracks will form between the board as they dry. If they are glued together , then there must be allowances for dimension change or there will be splitting etc.
A solid 30 inch wide tabletop moves quite a bit (1/4-1/2 and inch) over the seasonal change in humidity. Therefore the cross boards or cleats need to be attached in one of many ways that allow wood movement but still hold the tabletop firm and flat.
The simplest way is screwing the top thru the cleat in the middle and at the sides of the top. The side holes need to be slots in the direction of movement to allow for movement. There are special elongated washers available called expansion washers that facilitate the movement.
-
http://www.leevalley.com/en/hardware...=3,41306,41309. ( This should ling to lee valley under expansion washers.)
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Other ways are buttons screwed in the top and indexed in a slot in the cleat or s clips that do the same.
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http://www.leevalley.com/en/hardware...=3,41306,41309 this should show the s clips in use.
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I hope this helps woodworking if fun and useful. Understanding wood properties is vital to quality design. Designing for wood expanding and contracting if one of the ots important factors. It often starts with the best choice of wood for the project.
As mentioned above , construction lumber is best used for projects that will be fastened together firmly using wood construction techniques. Avoid tight circles/growth rings in the end of boards in furniture other than narrow pieces.
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post #20 of 30 Old 03-29-2014, 05:58 PM
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I forgot to mention about the bowing related to the growth rings.
It is definitely rustic but I think you can see the rings on the center and the left board. The left board has the center of the tree up and has warped with the cup up. The center board is the opposite .
Due to the grater movement tangentially vs radially, the board warps to flatten the rings as it dries. Thanks
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