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How to prevent Acacia desk tabletop from bowing?

Built this desk today using 2200 x 600 x 26mm Acacia Solid Oiled Hardwood and 73.2 x 50 x 6cm Rapid Mesh Steel frame legs from Bunnings. I set the legs 200mm in from the ends and 50mm in from the sides. The table top is already bowing. The distance between legs at tabletop is 1668, the distance between legs at carpet is 1670.

Can anyone recommend a solution and material required to brace the tabletop from bowing and do I need to brace the steel frame legs at the top and bottom to make them the same distance?

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Remarka6le

Hey , welcome to the Bunnings workshop community! It's great to have you here.

First off, nice desk, looks great 🙂 If I had this issue, I'd fix the bowing by grabbing an additional Steel frame leg (or two) and place it either in the centre at the back (for one) or evenly spaced on the left & right at the back (for two). Would look a little weird, but it would fix the issue.

If you owned the home though, you could always create a brace along the edge of that back wall and secure the table to it, would just mean you can't move the desk as easily.

Regards,

MitchellMc

Welcome to the Bunnings Workshop community @Bobnotabuilder. It's terrific to have you join us, and many thanks for your question about bracing a tabletop.

I wouldn't say this is typical for these project panels, and I'm surprised to hear that you built it recently and it's bowed like this within a day under its own weight. I would expect this type of bowing after several months of leaning on the centre, so I suspect something else is happening here. With a distance of 1668mm between legs, as @Remarka6le mentioned, an additional leg or brace would assist. Your desk is Acacia versus Teak, slightly thinner and not as wide as this desk, but let me mention the creator @robchin to see if he's had any bowing issues.

I'd imagine you'd have noticed any bowing before assembly, but were you storing the panel in a high humidity environment, like outside, for a while before bringing it inside? Did you lay it flat in this room to acclimatise for 48hrs? The reason for asking is that these panels are susceptible to humidity and need to be acclimatised to the environment in which they are being used. Say, you had it outside where the panel absorbed some moisture, and then you bought it inside and added the legs this type of bowing could be expected. Or, if you assembled the table outside and left it there overnight where it absorbed moisture, this bowing also wouldn't be unusual. In both these scenarios, the timber absorbs moisture and becomes much more susceptible to bowing than if it was dry. When acclimatised, the panel should be more than capable of supporting its own weight and likely that of a laptop, but when wet, it might struggle to support even its own weight. However, with legs spaced so far apart, supporting the midsection would be a good idea. I've had this issue with similar panels where I cut up several pieces and left them out overnight. They were all bowed and warped when I looked at them in the morning. The panels I had standing up and leaning against a wall outside were also bowed similarly to your top.

The issue you'll face now is trying to return the top to flat. A bracket can be placed to support the midsection, but if this is a moisture issue and the top has now dried out into the bowed shape, I suspect it won't be as easy to reverse the bowing. You might need to pack up underneath the midsection and then place those weights you have on either end to encourage the bow out of it. Alternatively, if the panel was outside before assembly, you could try taking the table back to that location and leaving it there for the same amount of time whilst supported under the midsection.

The bowing top has likely introduced the two-millimetre difference between the top and bottom of your legs, and you shouldn't need a brace for them. You can check this by flipping one leg around. If the distance remains the same, it's due to the top.

Here are the installation instructions for the product. For a bowed panel they suggest flipping it over and that should resolve the issue. You might like to place a couple of books at either end to elevate it slightly off your floor.

Please let me know if you have any questions.

Mitchell

Bobnotabuilder

Hi Mitchell,

Thanks for the response. Very strange as the panel was delivered by bunnings on Saturday. I installed the legs that afternoon and noticed the bow straight away. Slept on it and joined the workshop community the next day to troubleshoot.

I've purchased an additional steel leg frame at 73.3 x 70 to go centre back of the desk.

Will try flipping the tabletop and place books underneath. Thanks for the tip 👍

MitchellMc

That might be the issue, @Bobnotabuilder. It's advised that you leave the panel flat in that room for 48hrs to acclimatise prior to attaching the legs.

I'd recommend you flip the table, add the books on either end and place one of those kettle weights in the middle. Once it's returned to flat, you can flip it back upright and fix on your mid-leg. I suspect that the leg at the back will be enough to support the panel once acclimatised. If you experience further bowing, you could fix a length of 70 x 35mm Pine Framing Timber along the length of the table close to the front edge and spanning between the legs. Set it just far enough back from the front edge that it can't be seen from the front.

Please keep us updated.

Mitchell

Bobnotabuilder

Thanks @MitchellMc ! 😊

robchin

Thanks @MitchellMc for looping me in. I didn't have that experience but mine was a bit thicker. Still straight as.

@Bobnotabuilder I think I would've used a third brace for that - but easy to say that in hindsight.

One of the other things my woodwork teacher taught me more than 30 years ago was that if you are going to paint or seal a piece of wood or a panel - you have to do both sides and the edges to prevent long term bowing. Not sure that this is the case here but just thought I'd mention it.

Remarka6le

Awesome stuff @Bobnotabuilder , keen to see a picture of the desk once the installed the additional leg brace is installed. It being flipped like this would be a perfect time to install any cable management features to the underside as well.

MitchellMc

If that doesn't entirely fix the issue, you can place a book under the top at either end, raising it slightly, @Bobnotabuilder. That will allow the top to bow slightly in the other direction. Don't allow it to bow too much in the other direction, or you'll run into the same issue. You just want to over-correct it slightly.

Mitchell

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