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

I built this table about 10 years ago and it hasn't self destructed yet. It's made out or macrocarpa pine (monteray cyperus) and I sealed it with estapol 2 pack epoxy. The timber had been air dried for a number of years and then spent several years in the loft of my shed (just under the tin roof). Reckon that would have been close to the equivalent of kiln drying. I used the 2 pack finish to try and minimise moisture change in the timber. An impermiable barrier on the wood. There are certainly some timbers I wouldn't consider using for this type of construction.
Tony
Table 1.jpg


Table 2.jpg

Hi Barterbuilt,

There is no problem with building a table with a mitred frame around the top panel. The essential ingredient is that the panel within the mitred frame must float freely. This obviously precludes a tight join of the frame to the panel but that's OK.... there's lots of ways of making that look good also. Prepare a continuous tenon or attached spline right round the panel. Prepare a continuous slot around the inside of the frame to accept the spline or tenon. This should be just about zero clearance ie a tight push fit. Leave 6 to 8mm extra depth all round the slot for expansion and contraction of the panel. In the bottom of this slot very lightly glue in lengths of the rubber compression cord used to fix fly wire in the ally fly wire frame. ( You can buy special small rubber balls sold expressly for this purpose but there's no need for such sophistication). Glue and clamp up the job as normal. You will find that the panel centers automatically quite accurately ( dry fit first!!) and there's zero movement of the panel in the frame.. It's a good idea to spray polish the panel before gluing up so that when moisture change causes shrinkage of the panel you cannot see an unpolished line around the join point of the panel and frame.

It's common to see unworkable cross banded joinery in solid timber tables in showrooms. That doesn't make it an acceptable so please don't follow the 'professional' lead in this direction.

Cheers Old pete

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

Hi Tony, that's a nice bit of macrocarpa you have there.
Just a few thoughts (for the OP) perhaps it is a low expansion timber, and the finish slows the moisture moving into the wood and the joins are all splined at the corners giving enough strength to effectively control expansion, perhaps the timber was below say a normal MC content of 12% when put together and has only ever tried to expand as opposed to shrinking possibly leading to splitting and perhaps Port Sorrel doesn't have radical changes in humidity


Pete

Hi Tony,

Macro has very very low shrinkage levels across the boards compared to hardwoods. Only 3.3% green to dry if sawn on the back off and only 1.6 % green to dry if sawn on the quarter. End on shrinkage is minimal. I can't easily find figures for unit shrinkage around the 12% MC level but it would be minimal compared to hardwoods. I suspect that that is the reason your table top has hung together so well. Also the multiple elements used in your frame lessens the problem of differential shrinkage from the across the grain to the along the grain orientations.

I don't think from experience that any form of restraint applied to strengthen a joint in solid timber will arrest wood movement at the joint if it wants to happen.joint failure may take years to occur.

BTW it's well documented that clear lacquers do little to stop moisture movement in timber in response to changes in EMC %. I don't know if that applies to two pack epoxy, probably not, given how well it performs in wet areas where water is trying to get in not get out.Another reason your job has been successful!

A very interesting case study you have there: thank you for sharing.

Old Pete

Originally Posted by tony_A

I built this table about 10 years ago and it hasn't self destructed yet. It's made out or macrocarpa pine (monteray cyperus) and I sealed it with estapol 2 pack epoxy. The timber had been air dried for a number of years and then spent several years in the loft of my shed (just under the tin roof). Reckon that would have been close to the equivalent of kiln drying. I used the 2 pack finish to try and minimise moisture change in the timber. An impermiable barrier on the wood. There are certainly some timbers I wouldn't consider using for this type of construction.
Tony
Table 1.jpg


Table 2.jpg

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.

Originally Posted by Elill

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?

I think it is a bloody good idea, too. It would be even better with a photo so we can be sure of your technique, and not invent a second best solution.

Fair Winds

Graeme