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Table Top Challenges - Can't get it Flat

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Forum topic by fsutim posted 05-17-2015 05:17 PM 1059 views 0 times favorited 18 replies Add to Favorites Watch
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fsutim

17 posts in 569 days


05-17-2015 05:17 PM

I have recently had problems with two table tops that I have made. Each table was constructed using (4) 2”x10” boards. The challenge I am having is the two middle boards are flexing upwards instead of laying flat (Please see pictures).

I used a wood planer and then joined the wood with three biscuit joints on each board as well as pocket hole screws across the length of each board. I joined the boards by laying them finished side face down on my concrete floor with the underside facing up. I first inserted the biscuits from board 1 to 2 and then installed pocket hole screws on boards 1 to 2. I repeated each step from board 2 to 3, and board 3 to 4.

I would appreciate any insight as I am stumped as to why this is happening. I have spent too much time trying to flatten it with a belt sander rather than figure out the root of the problem. Please help.


18 replies so far

View bondogaposis's profile

bondogaposis

4028 posts in 1814 days


#1 posted 05-17-2015 05:59 PM

How is the top attached to the cross pieces? You are experiencing wood movement, you need to allow for it.

-- Bondo Gaposis

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TheFridge

5765 posts in 949 days


#2 posted 05-17-2015 06:03 PM

Need pics of underneath. Easiky fixed I would think

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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fsutim

17 posts in 569 days


#3 posted 05-17-2015 07:08 PM

I have not yet attached the top to the base. At this point it is still floating. Attached are a few pictures of the underneath side of the top.

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fsutim

17 posts in 569 days


#4 posted 05-17-2015 07:27 PM

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Kazooman

626 posts in 1416 days


#5 posted 05-17-2015 08:03 PM

Looking at the end grain of the two boards in question I would say you have a real challenge on your hands. These two boards were cut from very near the center of the log. With that grain you will get a lot of cupping with changes in moisture content. The two pieces are arranged with the grain pattern in the same direction so when they cup it is additive and the result is your center lifting. If the two boards were arranged to have the grain patterns opposing you might have better luck.

One solution could have been to rip the piece down the middle, flip one side end for end and rejoin the pieces with the opposing grain pattern. However, since you drilled for pocket screws you no longer have that option.

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WhyMe

614 posts in 1024 days


#6 posted 05-17-2015 08:32 PM

Exactly as Kazooman said. Wide dimensional lumber will cup so you need to alternate the growth ring direction to help minimize the cupping. To also help minimize cupping you need to cut out the center heart of the lumber.

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bondogaposis

4028 posts in 1814 days


#7 posted 05-17-2015 08:38 PM

I agree w/ Kazooman, the pith in both of center boards can cause you problems. I always try to rip out the pith at least 1” either side. You could still do it if you feel it is worth your effort. You have a nice table going there, if it were mine I would do it. The most import concern will be how you attach the top. I would use “Z clips” they are cheap and easy to use and allow the top to move w/ changes in humidity. Another option is to make slots in the cross members and use screws or lags from underneath.

-- Bondo Gaposis

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BroncoBrian

435 posts in 1422 days


#8 posted 05-17-2015 08:44 PM

Those are or are very similar to deck boards. Not much of a chance you can keep them from cupping. Alternating the grain will help, but each will move on its own. Using more narrower boards will be better.

-- Bigfoot tries to take pictures of me

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Kazooman

626 posts in 1416 days


#9 posted 05-17-2015 09:20 PM



Those are or are very similar to deck boards. Not much of a chance you can keep them from cupping. Alternating the grain will help, but each will move on its own. Using more narrower boards will be better.

- BroncoBrian

I hesitated to say it, but I think the best solution is to remake the top. The base looks really nice and it would be a shame to spoil the final product with an unstable top. I agree that more, narrower boards would be the best way to go. I would select the pieces carefully looking at the end grain to try to get pieces that will not cup so badly. They will still move with moisture changes and the top would need to be mounted accordingly, like with the “z-clips” bondo suggested.

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Homick

22 posts in 1384 days


#10 posted 05-17-2015 11:13 PM

How would one remake the top with the lumber he has? Rip the boards he has right at the center of the pith position and alternate the cup direction?

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BroncoBrian

435 posts in 1422 days


#11 posted 05-17-2015 11:25 PM

Homick – I was thinking that. But, the grain would still be at significant angles, they just are not good boards. It might help some.

-- Bigfoot tries to take pictures of me

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Kazooman

626 posts in 1416 days


#12 posted 05-17-2015 11:29 PM

Oops, responding to Homick: I mentioned before that this is not an option. The OP put pocket screws in the pieces. If he tried to alternate the cup direction the screw holes would be on the top side. At best, to salvage the wood, the pieces would need to be ripped outside the pocket screw holes. Then the top would be a good four to six inches to narrow. Doing this, and adding a new piece to make up the gap, would be one way to solve the problem. However, it would result in a strange patten of widths across the table top.

I would remake the top.

Note added since Bronco’s post: Yep, they are just not good boards for a table top. The grain structure will be a problem forever. Best to back up and remake the top with suitable lumber.

View Daruc's profile

Daruc

459 posts in 596 days


#13 posted 05-17-2015 11:32 PM

rip 3” out of the middle of each one and add new material.

-- -

View fsutim's profile

fsutim

17 posts in 569 days


#14 posted 05-18-2015 01:30 AM

Gents, I really appreciate the input. I will go ahead and remake the top. Would I still be rolling the dice with 8” boards or should I got as narrow as 6”?

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MrFid

805 posts in 1368 days


#15 posted 05-18-2015 02:13 AM

Welcome to LJs!

If you are buying dimensional lumber (i.e. 2×8s and such), buy the widest boards you can find since they are most likely to have at least parts of the board that are riftsawn. Remove the parts of the board that are flatsawn or even worse contain pith by ripping them out to make narrower boards. If you haven’t done so yet, do a bit of homework regarding flatsawn, riftsawn, and quartersawn wood. Plan to spend a while at the lumberyard (or home center, if that’s where you are buying wood) examining the end grain of both sides of each board you buy, as well as sighting down the board for twist, cup or bow. This time will be well spent because you will be able to use more of the wood this way. Also, out of curiosity, what do you mean by “wood planer”? This:

or this:

The first will not necessarily help solve any twist or cup issues you may be having unless you are using winding sticks or a suitable substitute method. From your second picture posted it looks to me like your boards aren’t truly flat and straight (this could also be due to the camera).
Apologies if anything I said was something you knew already; just trying to be helpful and it’s hard to know how much you know since you are new here.

-- Bailey F - Eastern Mass.

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