Thread: Allowing for natural expansion/contraction of timber in table tops?

Depending on the cut and the species I was taught to allow for 1/8 - 1/4 in per foot. Maybe things have changed.

As already pointed out it depends on the timber and cut used but I always like to make sure. I use a slot in the side rails and metal/wood clips/hold downs.
a top 1m wide can grow or shrink by up to 10 to 12 mm. Or some other means where by the timber can change without tearing the table apart. Never a good look

I prefer to make hard wood hooks with plenty of room for movement. I cut them just a little short so when I screw them into the table top, they pull down nice & tight.

I have used the metal fig8 brackets. They are neater but I still prefer the hardwood hooks.

Steve

I use sliding dovetails to attach the top to the frame. Quick and easy to attach and detach if repairs are needed also.

We constrain timber movement by using manmade boards, (mdf ply) for soild timber movement has to be allowed for, I looked at a couple "professional" tables the other day, they had used metal clips in grooves but hard up to the apron, no room for expansion, they might push the aprons out with expansion and it might be allright but it's not good, Ticky's example

Evan Dunstan in the Wood Review a while back looked at some "professional" tables and pointed out the faults in not allowing for movement, IMO it's too much a case of "don't worry about that, just get it out the door" kinda thing



Pete

I hope you guys don't mind me tagging on to this thread, it seems to be an info thread.
I am not ready to start yet so I don't want to start a new thread. I am still planning.

I've got an idea for a dining table.
I really like natural edge tables, the trouble is I want the natural edge on the end too.
So I want to make a frame with mitered corners and then have a infill panel in the middle. The infill will also be timber.
From what I've read here this seems to be a no no.
Is there any way around the expansion problem.
I've managed to get around all the other issues that will arise from this design,except for the expansion of the center insert.

I'll start a new thread if you wish, but it may be the longest thread in the history of this forum.

Thanks

Andrew

Originally Posted by Barterbuilt

I hope you guys don't mind me tagging on to this thread, it seems to be an info thread.
I am not ready to start yet so I don't want to start a new thread. I am still planning.

I've got an idea for a dining table.
I really like natural edge tables, the trouble is I want the natural edge on the end too.
So I want to make a frame with mitered corners and then have a infill panel in the middle. The infill will also be timber.
From what I've read here this seems to be a no no.
Is there any way around the expansion problem.
I've managed to get around all the other issues that will arise from this design,except for the expansion of the center insert.

I'll start a new thread if you wish, but it may be the longest thread in the history of this forum.

Thanks

Andrew

To reduce/control expansion use manmade boards like ply or mdf, I'd opt for a good quality ply over mdf, the ply is used as a base/ground onto which you glue your infill as a veneer and then fix your natural edge all around, depending on how thick you want the table top ply might be quite heavy, an alternative is a torsion box with ply skins top and btm (lighter) and then do the same as above.




Pete

Wood is a wonderful material, with many desirable properties from a furniture-maker's point of view, but it has one bad vice, & that is that it WILL expand & contract with moisture movement. You can slow down the process, but short of hermetic sealing, you cannot prevent water ingress/egress unless you live in an area where the relative humidity doesn't vary year-round. You can get away with screwing down table tops for a while, sometimes even a long while, if you keep them in a place where the annual moisture cycle is small, and if the width isn't too great (hence total expansion/contraction), elasticity of the species allows it to accomodate the stress, and/or the screws are able to bend or move a little in the frame. I sometimes use screws through elongated frame holes on small tables when buttons aren't a practical option, but it's usually an unnecessarily risky/lazy/silly (apply which adjective you prefer) method of attaching solid wood tops, when there are more sound and more elegant alternatives, as demonstrated above.

Some people think they can prevent wood from moving - good luck!. I could never convince my father that he was on a fruitless mission when he insisted on epoxying and screwing 3 cross-battens (with double & triple rows of screws!) under a Stringybark dining table he made. For a year or two, it all managed to hang together, but in the end, nature had her way, and several large cracks appeared along the top, both along & between the glue-lines. This demonstrates another rule of thumb, that the denser the wood, the more power it can develop.

And Andrew, I recommend you take note of what pjt suggests. If you want a panel inside a large frame like a full-sized table, you either have to use man-made materials with minimal or no moisture reaction, or allow for movement by constructing it like a frame & panel door. You don't need a gap on the long-grain ends as most woods have negligible movement along the grain, but you do on the short grain sides, and the amount depends on the species. The thicker & denser the wood, the more power it has, so the more you need to take note. Of course gaps are not a very good thing to have in table tops, they will soon fill with gunk, so this method is understandably not popular. However, without due allowance for movement, any solid-wood table constructed with a restraining frame is almost certainly destined for catastrophic failure at some point down the track.

Cheers,

Said so much more elegantly than I Ian.



Pete

Originally Posted by enak

I use sliding dovetails to attach the top to the frame. Quick and easy to attach and detach if repairs are needed also.

Thats a bloody great idea - nice feature too. Do you run them the length of the base or just a couple of short ones on each end?

good-day,

Barter-built have you seen "breadboard ends technique" - it appears to away of continuing the natural edge detail around the ends of the table top.

The method of jointing appears to vary - i suppose to your preference dovetails / mortice and tenon.

My understanding is the centre of the end board is glued and the ended are pinned using dovetails / mortice with pinned tenons.

have a look at

Joining Breadboard End with Mortise and Tenon - YouTube

The bloke doing the video does not say much but he does demonstrate how to it.

One point I have also heard when determining the length of the edgeboard you should allow for expansion

• So based on previous comments based on 1m wide top will expand to 1012mm - note you may want check the expansion - pending timber and cut as noted previously.
• I assume you would centre the board so 6mm overhang on each side,
• I guess that size overhang may look a bit ordinary, but similarly cutting the board to 1000mm and the top expanding to 1012mm would not look good - perhaps spilt the difference and go 1006mm and it should look good most of the time.
• Either way there should not be any cracks.

Good Luck - I am new to woodwork, but hope this is some value, and this is my first reply - glad that over.
Done

Chris

I need to miter the corners ,so the breadboard ends won't workout.
I wanted to make the center insert out of laminated strips of burl say 40mm wide.( originally I wanted to use 40 x 40 strips )
What would be the maximun thickness for the burl now if I am to "laminate" to a piece of MDF or ply.

Thanks

Originally Posted by Barterbuilt

I need to miter the corners ,so the breadboard ends won't workout.
I wanted to make the center insert out of laminated strips of burl say 40mm wide.( originally I wanted to use 40 x 40 strips )
What would be the maximun thickness for the burl now if I am to "laminate" to a piece of MDF or ply.

Thanks

I would suggest aiming for a thickness of about 2.5 to 3mm off the saw (bandsaw or table saw) maybe a little thinner if you have confidence in your method of cutting, I would cut them on the BS, this gives some allowance for some thickness sanding/preparation before gluing to the base and once glued down you should still have (if all has gone well) say 2mm for final sanding which should be plenty, no fear of sanding thru the veneer unlike with the production sliced veneers which are more likely to be 0.6 to 0.7mm thickness.



Pete

Just thinking about the mitred corners, I would suggest not going too wide with a solid surround piece, say under 100mm (species dependent) reason being is that old problem expansion, as the surround timber expands it will be moving away from the mitre join line and will tend to open up, especially if you have just cut and glued the mitre, strengthening the join with a spline/biscuit helps as does joining bolts Hardware for kitchen, furniture, school , Hardware.net.au-Hardware Online (the one in the pic marked other)

just another thing to consider in the total build


Pete