Help, advice and whatever else you can offer

[Martin du Preez]

Hi there i'm looking for some advice. im just starting to diversify into this field and get lots of lovely wood from tree work. i wanted to start of with something small, want to make a coffee table out of a metre diameter oak ring. how do would you go about preparing and finishing the wood? its well seasoned! thanks in advance

 

[Chippy]

Have a look at this

 

 

[Woodworks]

A ring of any species is almost certain to crack badly as it dries. Found this that looks like it explains it better than I can. You say it's well seasoned but is it dry inside? If it really is you should be OK

 

 

Wood shrinks by different amounts in different directions. There is almost no shrinkage in the direction of the wood's grain (lengthwise). There is some shrinkage radially (perpendicular to the growth rings), and a greater amount of shrinkage tangentially (along the curvature of the growth rings). The cracks in the end grain of this partially dried firewood at left illustrate this concept. The firewood had only dried at the ends when the photo was taken. Shrinkage is thus only at the ends, while the middle of the wood has not shrunk as much. Cracks have opened up at the ends to make up the difference. The cracks are mostly perpendicular to the growth rings, because there is more shrinkage along the direction of the rings (tangential shrinkage) than there is perpendicular to them (radial shrinkage)

Once the wood has fully dried throughout, the whole piece will have shrunk by the same amount. With the center of the wood as shrunken as the wood near the ends, the cracks will mostly close up again. 

The different rates of radial and tangential shrinkage can cause distortion in wood, such as cupping of boards. It can also cause radial cracks from the center of the wood to the edge, as shown in the photo at left. This is because the circumference of  the wood shrinks more than it's radius, and the big radial crack essentially allows the remaining circumference to shorten.

It's generally best not to have the center of the tree trunk as part of the board because of this. Beams used in timber frame construction usually include the center of the tree, and usually have cracks along the flat sides because of this. However, that is considered an acceptable defect. 

Edited April 3, 2018 by Woodworks

[silky fox]

Very interesting. I do however have a Birch ring about the size of a dinner plate and one centimetre thick that dried without any splitting whatsoever.

[openspaceman]

2 hours ago, Woodworks said:

Once the wood has fully dried throughout, the whole piece will have shrunk by the same amount. With the center of the wood as shrunken as the wood near the ends, the cracks will mostly close up again. 

This is the salient point and where the art/science of kiln drying for lumber comes in.

 

Most of the problems of cracking occur because one part of the wood dries before the rest. Shrinkage occurs once the water in the cells is gone and the water associated with the cell walls starts leaving. So if one part is still full of water and the other  dries below its fibre saturation point then the wood is strained and pulls apart.

 

What kiln drying or air seasoning does is to only allow water to leave the cut surface at the same rate  that water is able to migrate through the wood.

 

Thus a ring dried homogeneously  can stay as a ring without splitting as Silkyfox says.

 

It will be species dependent though as every species has a different ratio of tangential to radial shrinkage, when this is high the tendency to pull apart down the radius will be higher and it will also be influence by weaknesses, like those associated with parenchymous tissue (rays and figure).

[Woodworks]

But the reason a ring cracks is not to do with uneven drying. The ring is the key here. A circle cut from board without the centre of the tree would stand a better chance. From my previous post

 

"This is because the circumference of the wood shrinks more than it's radius, and the big radial crack essentially allows the remaining circumference to shorten."

 

Yes sometimes you get lucky more so with small diameter material but the OP is talking about a ring a meter in diameter! I dont want to put a downer on it just being realistic that an oak ring of a meter diameter has a very small chance of drying out without cracking badly.

[Martin du Preez]

Cheers for the info guys, not worried about cracking these oaks are dead standing since I was kid, utterly petrified. Just wanted to know the process, sanding down, oiling varnishing? What's best to bring the colours out ?

[Lazurus]

I use Danish oil almost exclusively, easy to apply, reapply and gives a lovely finish, can be built up from soft sheen to high gloss.

[Lazurus]

If you end up with a split you could always do a resin infill.

[silky fox]

That's rather a nice touch Mr Lazarus....