Thread: Table Construction

Ive seen lots of tables made with these types of legs, usually the top bit is 8 or 10mm steel though!

These are the options (in my opinion):

• warn them and let them decide if they want to take the risk
• if yes screw it on
• if no there are 2 solutions

1. just use a bigger drill bit to make the holes bigger - charge them to do so
2. ask them or offer to find someone to make a new set of legs with appropriate holes

From my understanding screws do allow for a little bit of expansion but like qwertyu said make the holes bigger and use washers. The secret is to tighten the screws just enough to hold the top in place, but loose enough to allow it to expand & contract.

Originally Posted by EagerBeaver71

From my understanding screws do allow for a little bit of expansion but like qwertyu said make the holes bigger and use washers. The secret is to tighten the screws just enough to hold the top in place, but loose enough to allow it to expand & contract.

This style of leg relies upon the fixing from the legs to tabletop to provide racking resistance, i.e. the tabletop is a structural element, hence the wider top plate and multiple screw holes. They also tend to be used with composite surfaces, i.e. veneered MDF, birch plywood, etc. which do not move significantly.

For a free-standing table IF you do not tighten the screws sufficiently then over time they will progressively become looser until it fails. For say a desk that is against a wall or in a corner that is not such an issue.

Quality manufacturers of similar tables tend to make the frame self-supporting so that it does not require the solid wood tabletop to be a structural element.

A better solution would be to add another structural element between the two frames to provide that racking resistance and to allow for the inevitable wood movement.

It could be as simple as two powder coated / painted steel / aluminium 50 x 50 mm angle/s or SHS that is securely bolted to the underside of the supports at say the second row of holes in from the ends of the supports. They will be hidden from view and clear of knees under the table. Then fix the tabletop via the enlarged outer holes thus making allowance for wood movement. Spacers / packers may be used between the frame elements and tabletop as necessary. That then makes the table secure and also more easily transportable.

Convert the screw holes in the steel to slots and it should easily allow for movement.

How wide is the base? Will stability be an issue?

Ive been using KD US White oak for the last 30 years in volume . I fix bread board ends to 1 .1 wide meter tops and at most Ive seen 1.5mm movement each side after viewing the tables years later. 99% of the movement is around .5mm each side. That's on tops sealed one side only . If its a worry seal both sides. You wont get bad movement unless the table is left in a cooking hot sun for some time or its involved in severe water damage like a flood or leaking roof that isn't discovered for a week or two.

If you want to elongate the holes just do the outside one or two sets of holes and leave the middle. Just drilling them larger will work as well.

Bread board ends are a good test of movement . Much more than a table base.
And just screwing a top down does have some give . Look under any rigid Antique table base and top and your never going to see elongated holes for top movement . The holes in the timber base on them allow a screw to wiggle a touch and that's enough. Under pressure the screw holes in the top compress . Screws bend if its bad enough, but out of something like 44 years of repairing and making tables Ive rarely seen that. If it had that then it would have been flood damage or similar.

Another thing . You supply kiln dried top well made and if there are no complaints after a month or two any movement after that is how they treated the table . Just charge them if they miss treat the table and they want it fixed.

Rob

In a pinch, you can convert the screw holes into slots with an angle-grinder & a 'thick' cut-off disk, coming in from the top side.

When doing this, I don't actually elongate the screw-holes, instead I stop as the bottom of the cut just barely starts to cause elongation. Constant checking of depth - and a modicum of care! - helps prevent any obvious bluing of the steel apart from immediately around the screw-hole (which will be covered by the screw) and if there is more movement than expected,it's the screw bumping up against a thin edge which will deform out of the way.


(This is an approach we used to use when fastening timbers directly to I-beams, such as panelling. For those golden "architect-designed" moments. )

In my very humble opinion, I've seen so much on the subject now to suggest too much is made of wood movement when it shouldn't have to be. In the beginning as an enthusiastic novice its the one thing that almost put me off making anything. Some things cannot be taught and experience is one of them, thats why I listen to only the most experienced people who have vast amounts it. So like Rob said its only relevant when there's various weather extreme 's.

Thanks for all the wisdom and advice. I must admit I am one of the novice that are really concerned about movement. Was instilled in me by an expert craftsman that only makes heirloom pieces.

I spoke with the manufacturer and they stated (after I suggested it was required) that elongated holes have been previously recommended to them however they have had no issues to date. I note that they only warranty their tables for 2 years.

Not a guarantee but a positive sign.

I have provided this info to the client so will see what they think. Either way i will enlarge (not elongate) the outer holes in an attempt to reduce some of the risk.

The issue with wood movement is typically a poor understanding of the wood drying process and an eagerness to use wood before it has been seasoned / dried sufficiently for the application / use. The bulk of shrinkage occurs in the drying phase, with relatively little seasonal movement (when compared to the initial drying shrinkage). This is accentuated by the fact that few makers have the luxury of extensive wood inventories which allow the wood to reach ambient EMC (equilibrium moisture content) on their premises before use.

Wood movement can be an issue with very significant consequences in particular applications, parquetry floors, or any natural wood floor, even furniture. Well designed & constructed pieces allow for some wood movement however carefully seasoned wood is better insurance.

The scale of a project, the delivered EMC (equilibrium moisture content) then the ambient EMC the wood will finally reach determines how much of an issue wood movement will become.

Those with traditional tongue and groove wood floors can attest to how much seasonal shrinkage / expansion does occur. As the relative humidity changes, gaps will appear in the "dry" then close up again in the "wet." Experienced tradesmen allow for this when laying a floor, cramping up tight in the wet, or loosely in the dry.

I was just wondering if the 12-14 weeks lead time that workshops advertise have more to do with EMC then they do with a backlog of work…

Originally Posted by Damienol

I was just wondering if the 12-14 weeks lead time that workshops advertise have more to do with EMC then they do with a backlog of work…

12-14 weeks is backlog of work. Or is for me and other workshops I know of. If I didn't have any work and then got a job the timber would arrive and I'd start it that day.
As it is now with work stacked up for 6 months the timber that has been delivered for all that work is just stacked board on board not stickered up to breathe and change with temp or equilibrium moisture content.

You have to consider what you are making and machining boards to a little over size and letting them sit and breathe for a day or two if its important like a top, is a good idea. A big consideration is the width of the work.
I machine a top and lean boards against a wall to breathe and then go onto legs and base work for things like 1 M or 1.1M wide tops. Once a top is together waiting for bread board ends or mitred surround I cover it each night until its sealed.

If its an extension table, with 2 ends and 6 leaves I take a LOT more care with the tops and let the boards breath throughout standard average days but stack and cover at night. If you have a standard set of days with average over cast mid temps throughout the week as your making it then leave the tops out all over the place and go home for the weekend and the weather turns hot and dry. Come Monday morning your coming to work to find you will have to re make the whole set of tops again. Cut each join and re do if your lucky and have a touch of thickness on your side.


Rob

Expect a mm of movement per meter of width. I'd factor in 2mm... Drill the holes out and use washers. Don't crank them down and everything should be fine.

Tell the client direct sunlight and underfloor heating will void any warranty.
It’s unbelievable where people put solid timber furniture, Architects are the worst.
No idea about materials whatsoever.
H.

Originally Posted by The Spin Doctor

Expect a mm of movement per meter of width. I'd factor in 2mm... Drill the holes out and use washers. Don't crank them down and everything should be fine.

I was taught 1 - 2% which would translate to 10
- 20mm