How to flatten warped mango wood tabletop slab?

[AntonT]

   

I have a mango wood slab I am using as a tabletop for a bar outside. 

One side has warped and sits proud of the base. 

I was thinking of putting wood above and below and clamping it down to allow me to screw it to the tabletop but I thought someone may have a better idea. 

See photos. 

[Noyade]

"I'll start by trying the low tech solution first."

Absolutely!

Sorry, one last whiteboard thought and then I will let it rest in your capable hands.

You never said if you wanted the top free of bolt heads?

I was thinking of round-headed bolts from the top, buried - but I think one problem would be that table frame was never intended for the slab and would be made of thin square tube?

Crushing forces to get that slab down - would most likely distort and compress the horizontal tube members.

Hence...

A welded thick plated 'U' section to absorb the forces.

Hope it makes sense.

Cheers.

[AntonT]

That does make sense. I'd rather not see bolts. 

I will work through the options and report back. Might be a while though. 

Thank you to all who contributed. Some really clever solutions. 

[Nailbag]

Hi @AntonT 

Apologies I'm late to the conversation. My suggested solution is a combination of @Noyade and @Dave-1 and one that I used to straighten a mates  spotted gum top that was warping (about 10mm). Like yours, his gets battered by the weather being on a 2nd level alfresco. It too was never secured well to the timber frame underneath. It's almost an exact scenario as yours, but you already have the steel frame that we needed to get made up from another mate who welds.

I have attached some photos below of how I/you could also go about it. Instead of weights allowing time to eventually flatten the top, I used 25mm square tubing across the top that was G-clamped to the steel frame. Then using length of round tubing as leverage to carefully wind in the clamps just a small amount each day. I sourced an old 2nd hand pair that were much bigger than needed for the opening, but had the thicker handle that wouldn't bend as I tightened the clamps.

To help soften the top, I soaked in hot water a couple of beach towels that I wrapped around the end of the top. I then slid over them a large bin liner which contained the heat and moisture. After an hour, I had a go at retightening as any little bit helped. I hand-balled to my mate the daily process of a little bit of tightening - wrapping hot towels - a little bit of tightening. It took about a week to get the board flat to the new metal frame. The top of the frame had pre-drilled holes every 150mm to accomodate galvanised 50mm hex head screws (rubber seal removed).

Hope this helps. Nailbag

[AntonT]

That is very helpful. My Dad was a serious steel and wood worker and has proper industrial strength clamps and some heavy duty tubing which I'll have access to in a few weeks. 

He also has a steamer that I might add in to the mix. 

I'll let everyone know how it goes.

Thank you to everyone who took time from their day to help me. 

This community is awesome. 

[AntonT]

So it's been a while so I thought I'd give you an update. 

Warp is slowly coming good. Sides are nearly level after small adjustments daily. I will put in some decent screws and add a couple of brackets. 

Then I'll work on the end warp to see if I can get that flat as well. 

Does anyone have recommendations as to what screws are best for a very soft wood? 

Patience still seems to be a virtue. 

Updates to come. 

  

 

[Dave-1]

Afternoon @AntonT 

Absolutly love it! That is coming along slowly but nicely. really nicely in fact.

As to screws... Mmmmm Id prefer bolts but then if you wanted it to be smooth. Think I will let someone who knows more about timber screws and grabbing answer this one  

Brilliant work and thankyou for keeping us updated

Dave

[EricL]

Hello @AntonT 

I was going to suggest using countersunk stainless-steel nut and bolt assembly. But there is a limit to its length, another option would be to use a midsized cup head bolt and countersinking it into the table and covering the top with filler. Plus, there are also galvanized countersunk options, but I suggest visiting your local store and checking what's available. My best advice is not getting anything smaller than M8 so that it will provide enough holding strength to keep the benchtop down.

If you need further assistance, please let us know.

Eric

[AntonT]

Thank you. I was thinking M8. Really just wondering what thread holds soft wood best.

I'm trying not to use bolts which is why I'm thinking off adding brackets.

The wood is so beautiful it would be a pity to use filler. 

[Jewelleryrescue]

Hi @AntonT 

You have a  lovly wooden top.

I would  pre drill 4mm  the tables  metal  frame  underneath to  allow screws through going up into the wood top and use screws to pull the mango board down to the metal  frame taking the bow out.  Make sure screws are not too long and go through the top.

Add screws  gradually and tighten them bit by bit pulling the timber into flat to the frame.  I would pre add some  builders  liquid nails on the top of the metal frame first so  once screwed down  it will help hold it forever.

The mango top in time will conform to the flat shape with out pressure.

Have  fun.

slip some timber strips to fit in under the plank to fill the gap size  usinng simply builders glue.

[AntonT]

Thank you. 

That's pretty much the plan. Just being patient to try and relieve as much stress on the wood and screws before removing the clamps. 

Will still tighten a little before screwing. 

Good idea about the liquid nails. Certainly won't hurt.