Thread: You guys. Bowed Tabletop

some pics of the bowed section and the underside will help

please, will help.

Cheers
Michael

too slow

One question: was the table finished on the underside as well as the top?

Try to include some pics of the ends of the boards pls.

All of what they said plus how was the top attached to the frame?

Originally Posted by Skew ChiDAMN!!

One question: was the table finished on the underside as well as the top?

And did you recently have a lot of rain ,
ie
heavy dampness in the air for a few days ?

Did the top bow up or down , up at the sides or up in the middle ?

The table was finished on both top and bottom. It has taken two years to get to this stage but most of the movement was in the first few months. Rain in Melbourne, yes. It appears the top has bowed up at the edges but there could have been a slight drop in the centre also as the timber frame is quite thin.

I will get some pics up tomorrow.

Originally Posted by middy

The table was finished on both top and bottom. It has taken two years to get to this stage but most of the movement was in the first few months. Rain in Melbourne, yes. It appears the top has bowed up at the edges but there could have been a slight drop in the centre also as the timber frame is quite thin.

I will get some pics up tomorrow.

Interesting thread. The most obvious way that I can think of making it true is will involve some cutting. Here's the deal: You're describing a 'cupped' board, whether it's joined or not.

It would be helpful to know how many boards are actually joined.

You could straighten the top mechanically (with angle iron or other method) but that will almost certainly result in the top eventually splitting. The stresses in the timber will not go away!

My recommendation: Rip the top along the existing joins if possible (if not, then between them....yes, you will end up with more pieces, but that's not necessarily a bad look!) Once they are ripped, simply place every other board upside down and re-join. Once it's joined again, plane or sand back to flat, and you'll be right.

I take big tops to a commercial joinery place with one of those monster drum sanders. One pass is all that's necessary, and that's how they charge...x number of dollars or beers per pass.

As per other posts, once it's back together, do seal both surfaces!

Hope that helps.
Michael

PS- In the future, do try to buy quarter sawn timber so that you don't run into this problem. (Hint: The end grain will be vertical if it's quarter-sawn....much less movement, which is why it's so desired as a milling profile. Victorian Ash is plantation grown, kiln dried and quarter sawn as a matter of regularity these days!)

A stab in the dark

You said you used Tassie Oak which is almost always quarter sawn so I don't think that cupping of individual boards is the trouble. I do not know your experience with wood so I will guess that you are new to its use. From your description I think you may have made a common mistake.

Wood expands and contracts across its grain and does not move along the length of its grain.

If you have fixed your top to your frame, which is at 90 degrees to you top and not made allowences for the movment of the wood then it will bow up and or down then eventually crack as it expands and contracts.

You said the bowing mainly occured in the first few months which makes me think that it was not as dry as it could have been when you fixed it to the frame. It has then dried causing the top to contract, the frame can't contract with the top as its grain is at 90 degrees to the top and so the top will bow up at the edges as you have described.

Try removing the fixing that hold the top to the frame and let it sit a while to see what happens, even a little bit of weight on the edges may help, if it comes back to reasonably flat then get some slotted brackets (25 x 25 steel angle) to fix the top back allowing it to float as it should. See the drawing I attatched.

As the other guys said, it is hard to work out without knowing your design so I am just taking a punt on it being the sort of error I have seen many times before.

Good luck and I hope you can get your dinner time conversation back to better things.

Jim

May Mastotermies never find your wood stocks

Thanks for your help with this guys.

As you can more than likely tell this is my first attempt at making furniture. The table was designed to be used in a real estate office to open plans etc on with the intention that at some stage the legs would be chopped to become a dinning table. The time is nigh so any help would be appreciated.

I was expecting that I might have to change the boards that run between legs to something a little more substantial and was hoping a combination of this and some steel / alloy supports may be enough.

I also think the two supports underneath will have to go as they are more than happy to bow with the table (if not assisting in the first place).

A few points:

The method used to secure the top and the frame is not adequate because:

a) it is not strong enough and

b) they do not allow for movement although their weak strength might allow for movement more by accident than design

Use buttons as suggested earlier.


You need to try and figure out why it has moved. If the timber for the top was not evenly dry prior to joining then that could be the cause.

If the top was uniformly dry prior to joining then perhaps the top and bottom have absorbed moisture at a different rate thus causing uneven expansion making it curl up. This could be caused by different thicknesses of finishes used for top and bottom.

It could be a combination of both.

It is possible that making substantial buttons might pull it back into shape but if trying this, make sure the top is conforming to the frame rather than the frame conforming to the top!

You may need to ensure the top is uniformly dry and then rip and re-join if the buttons can't pull it back.

The supports underneath if at all necessary should allow the timber to move using slotted holes for the screws.

Please take my comments as suggestions rather than harsh criticism.