Jointing a Large DIY Oak Tabletop

[Stuartgb100]

Have been asked by a friend to advise a friend of his, as follows;
How to proceed with jointing his oak tabletop, and finishing it.

His Intentions:
To create a rustic-looking octagonal 50mm thick oak tabletop, approximately 2400mm in diameter. It does not have to be perfectly flat.

Background:
Some two years ago, he had a couple of mature oak trees felled and then sawn into waney edged planks (55-60mm thick).
The planks were then stored horizontally (with spacers) in a roofed barn, where sides were open enough to allow good airflow, but also rain protection.
Some six months ago, he began to prepare the top using hand tools only.
He biscuit-jointed the planks and cut them into manageable pieces.

Where we are now:
The individual segments are wedge-shaped and of varying dimensions.
They are all approx. 53mm thick, needing final thicknessing.
At the outer side of the wedge, they vary from approx. 350-500mm wide.
At the inner edge, they vary from approx. 75-100mm wide.
They have been moved into a large living room, laid out to final shape and supported by a frame from an old farmhouse kitchen table.
The only means of heating is from a large wood burner, close to one side of the tabletop. It was going full blast when I visited (New Year).

What I have suggested so far:

• Build a larger support frame that will give more support to the outer edges of the individual sections.
• Take initial moisture readings and keep a record for each segment.
• Rotate the segments away from the wood burner, periodically.
• Turn the segments over, periodically.
• Check each segment for cupping, ends splitting etc.
• Take regular moisture readings.

This weekend, he gave me an update:

• Moisture content varies from 12-14% (so a drop in 1-2%).
• No appreciable cupping or bowing.
• No appreciable splitting at the ends.

So, my questions for the forum please:

• Have I advised correctly, so far ?
• Should he be doing anything else ?
• What moisture level needs to be met ?
• When can the segments be connected together,
• because he’s anxious to get on with it ?
• What method to use for jointing the segments ?

My thoughts on jointing:
The surface of the tabletop will not be uniformly flat, since he’s only using hand tools over a large surface area.
He’ll need to be able to dismantle the top.
I’m inclined to suggest a long tongue which will run full length to the centre of the tabletop, but stop some 50-75m from the outer edge (for a better visual effect).
For the tongue to work, the edges of the segments will need to be of uniform thickness, and the slot for the tongue will need to be exactly in the middle of the thickness. The tongue will not be glued.
He’ll need to build his permanent octagonal table frame, and then make suitable individual packers to support any discrepencies where the top doesn’t rest perfectly.
The top will not be fixed to the frame, but blocks can be fixed inside the top of the frame to stop any sideways movement.

Thanks for reading.

Cheers.

 

[Sgian Dubh]

• Have I advised correctly, so far ?

Probably not if the idea is to ensure no gaps ever developing between solid wood pieces as per the images you've included in your post. The end result is likely to be something like below, but with larger gaps, which will change over the seasons. The fact that the examples below are two relatively small squares each made of four bits of wood mitred together, biscuited and glued is not relevant. What is relevant is how the wood has changed dimension across the grain with changes in moisture content leading to the gaps. It's also true that I created these two panels or boards specifically to illustrate this type of failure for a timber technology text I was writing. Slainte.

 

[Jacob]

Looks doomed to fail.
I'd wonder about achieving the same sort of effect by not joining the boards at all but having them loose to drop in and/or on to a suitable sub frame. Or just joining alternate pairs. Perhaps pegs to locate them on the frame. Or something.

 

[Cabinetman]

Yes, Richard demonstrated extremely well the effect I was going to mention.
So what to do about it? The wood will move - that’s a fact, and the wood is already cut into triangles which gives very little room for an alternative design.
Personally I think that as the wood has to be allowed to move design around that movement. The only (and not something I would normally suggest) way really is to have built in gaps between the triangles, and make a feature of it. An attempt to infill the gaps? Well it would have to be flexible stretchable and squishy stuff - can’t imagine what it is or how it would work really.
Perhaps a sheet of glass on top of the moving pieces?
Ian

 

[Stuartgb100]

Many thanks - food for thought !

Trouble is that he's desperate to get it finished.
I guess we've all been there.

If it were me, I'd just lay them out and leave them loose, butt-jointed, for at least a year.
Each segment is too heavy for someone to accidentally move whilst they're at the table !
If there is significant movement, then a repair could be undertaken more easily.

Is there a consensus that over time, movement will settle down and become negligible ?

Cheers.

 

[Sgian Dubh]

Is there a consensus that over time, movement will settle down and become negligible ?

No, there will always be changes in the width of those pieces of wood in service in response to seasonal changes in relative humidity and temperature, although the amount of seasonal dimensional change will become less pronounced after a few years. Slainte.

 

[Jacob]

Designing to accommodate movement is a major feature of working with wood, perhaps not appreciated until you find out the hard way!
Looking at the layout - maybe it'd work simply having the whole thing in two semi circular halves, with an open joint between them. Possibly have battens underneath each half with slotted screws, to keep them flat but able to move, like a drawing board.
I doubt the tongue idea would work keeping them together, just loosely butted together instead.

 

[niall Y]

The effect your friend is after could only really be achieved if the top were thin veneers on a MDF board Large mitres in solid wood will always open up.

I once worked on a job where the unfortunate customer had, had all the flush doors made for his new-build out of solid oak. The design comprised two vertical stiles, with the space in between being made up of a continuous rub jointed board with the grain running at right angles to the stiles. Needless to say this central area split horribly

This too was a design that could have worked, but only by veneering and lipping board material.

 

[Stevekane]

Would it be possible to join each board with substanial loose tounges and assemble as snuggly as you could, perhaps using kitchen worktop bolts?then cut a hole in the middle which could be covered by a cap, as the top shrank the segments could be tapped further in so they are tight again, this would be an ongoing thing untill the wood eventually ( as much as it ever does) settled, when a final refinishing of the edge could be done.
Btw, I think its already a great looking table.
Steve

 

[Jameshow]

How about a octagon frame under and the table top floating on top, only the middle of the stave screwed down.
The gaps can be clauked with yacht deck clauking. Perhaps rasing the room temp a bit so the oak is dry before reducing it and standing a bowl of water nearby?

Or just do it during a dry summer's day.

Thereby the gaps will tighten.

 

[paulrbarnard]

Would it be possible to join each board with substanial loose tounges and assemble as snuggly as you could, perhaps using kitchen worktop bolts?then cut a hole in the middle which could be covered by a cap, as the top shrank the segments could be tapped further in so they are tight again, this would be an ongoing thing untill the wood eventually ( as much as it ever does) settled, when a final refinishing of the edge could be done.
Btw, I think its already a great looking table.
Steve

Beat me to it, tounge/dominoes and worktop bolts. This is probably the only semi viable option. Live with it for a year and then tweak the joins to minimise the gap based on experience of the finished table

 

[toolsntat]

Use no adhesive.
Dowel the sections together.
Make a suitable flat/decorative hub for the centre to receive and make captive the ends of all the sections.
The hub could be in two halves which clamp down upon the sections for adjustment and from the underside, provide an anchor to whatever sub frame is utilised.
This next bit needs careful thought and execution....
At a suitable distance from the outside periphery and centre of thickness drill oversized holes laterally in the sections to receive a wire rope of adequate proportions and looped/crimped ends.
In the underside of one of the sections create a pocket terminus to accommodate the looped and crimped ends of the wire rope and a turnbuckle.
It may be that to facilitate enough contraction of the loop that another turnbuckle is utilised.
This method could come unstuck if the section edges havn't had enough attention to create squareness but as with alot of things its all in the preparation.

After time and shrinkage, disassemble, make adjustments and reassemble.
Cheers,Andy

 

[Wood4me]

Considering from initial concept you have known, and stated, that the final finish will a little ‘ rustic’ and not quite flat etc I feel there has been far too many negative responses here that don’t fit the ‘brief’. I love it , what a brilliant idea to pursue with limited equipment. For sure the way to go is the worktop bolt principle. I would tweak it by using stainless 8mm x 100mm studding with about 40mm diameter recesses for washers and nuts on the underside. 2 or 3 per joint. Not in slots like worktop bolts but drilled 8mm holes from each edge , ideally in the middle of the thickness. Maybe also 16mm dowel between the bolts . Then tweak as required over time .
I reckon this concept would fit in with wanting to get this table in use as soon as possible. Once again great concept, you must run with these one off personal ideas .

 

[Beau]

One alternative approach to the expansion and shrinkage problem is to glue and seal it with epoxy. The wood would need to be good and dry first 10%-12% max. The epoxy will completely seal the wood so it won't be affected by variations in humidity. You should even go as far as using some sealant around any fixing in the underside. I should add I have never done this on furniture but built a wooden boat that's been watertight for the last 15+ years all thanks to epoxy.