Category: green woodwork

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Wood warp, how wood moves.

I found a couple of small planks in the workshop that I had forgotten about.They were dimensioned  them so that each was exactly the same size. The only difference between them was that one was tangentially cut and the other radially cut, I even wrote their measurements on them. They had been sitting near my stove for over 3 years, so I can truly say that they are now seasoned. The wood is aspen.

A lot of you will know how wood moves, but if you are starting out then it can all be a bit of a mystery. In order to work competently with wood we must know how wood moves as it shrinks and dries. It can be easy to get caught out and find that the project you have been working on has now warped or  shrunk in such a way that is no longer saleable.

The above diagram should be self explanatory. Tangentially cut wood is also know as through and through cut or flat sawn, and I am sure is also know by many other terms as well.  (1) in the diagram is a radially cut, or quarter sawn  wood. Radially cut wood can be more expensive because it is the most stable and often has lovely medullary ray patterns on the surface, as in quarter sawn oak, or lacewood in London plane.

The above photo are the aspen planks. The top plank in each photo is tangentially sawn wood. The bottom is radially sawn wood. The discs are oak turned green and allowed to dry. They have been arranged on the aspen planks to show the grain orientation and to give another visual way of seeing in what planes the wood shrinks.
Click on the image to make it bigger.

Turned green oak and dried, then cut into discs. The measurements are 32.55mm and 28.88mm making  a shrinkage of 3.67mm.
We can see that wood shrinks far more along the growth rings than across the growth rings. 

 The above faces (widths) of the aspen have the relevant end sections pasted onto them.
Radial on the left; green size 83.10mm dried width 81.50mm which is a 1.6mm shrinkage
Tangentially cut on the right; 83.65 and dried width 78.50 which is a 5.15mm shrinkage.

 The side view of the planks (depth)
Radial on the left 29.15mm green, 28.21mm dry, 0.91 shrinkage
Tangentially cut on the right, green 29.05 green, 28.58 dry, 0.47 shrinkage.

This is a 19.5 inch wide oak plank 3 inches deep. There is no way that this could ever be planed down to 3 inch thick plank, you would be very lucky to get 2.5 inches deep planned plank from this. Note how it has shrunk more at the ends and is thicker in the middle. All flat sawn planks will cup, even kiln dried stock that has been planed and thicknessed flat will still have a tendency to cup over time.

I have not talked about dimensional change in the length, well there is none to speak of, especially in short lengths of wood. My bit was exactly the same length. I am sure there will be a slight reduction in length, but I have never set aside a 12ft plank and measured it green and dry.

This is how a bowl shrinks as it dries. I love how the wood always has the final say in pole lathe turned bowls.
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Bowls, from heavily spalted to creamy white

I was asked recently to turn some bowls for a client from his old chopping block he used at work. He worked in the Forestry Commission and decided to take redundancy and move to Spain. I had my doubts about turning seasoned hornbeam on a pole lathe. It is, as you can see, heavily spalted. Splating is what we call the patterns you see in the wood caused by fungi eating the wood. Let the spalting or rotting go to far and all you get is wood that is now sponge. Once the wood has been dried the rotting stops.

The wood sat outside in the rain for a couple of months, this helped with getting the wood wet again and softer to turn. I was worried a bit about the softer, spongier portions of wood, which turned well in the end, a sharp hook tool helped. The serving spoon was made from half of the centre portion of the log.

Spalting this far gone is not quite to my taste, I prefer something a bit more subtle. The form of the bowls and especially of the spoon get lost, it is all about the marks, lines and colours of the wood.

This is the level of splating I prefer, these are beech bowls.

This is the other end of the scale, silver birch which comes out white and very little in the way of figure in the wood.

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Scots pine and fan birds

Scots pine

I now have a year’s source of wood for making fan birds – actually, it is probably more than ayears worth – it depends on how many I make and how many workshops I run.
The Forestry Commission at Haldon, Exeter let me have a Scots Pine tree. Ian Parsons (one of the rangers) and I choose the tree, straight grained and slow grown. This particular area was planted with Scots pine, and unfortunately the soil is not good so the trees never grew very fast, and do not have any real commercial value. They were planted in 1926ish, the biggest trees are about 14 inch diameter and the smallest are 5 to 6 inch diameter.

I like Scots pine, a native to this country; and not too resinous, unlike some of the other softwoods. It works very well green or dry and I have made small spoons from it in the past. I will also give it a go on the pole lathe and see if it makes a decent bowl.

The tree was felled at about 9.30am and by 11 am I had made my first fan bird from it. Some woods need to be mellowed or dried out a bit before use, but not this one.

I think this one tree could potentially make around 400 fan birds, and at an average of £20 each – that is good value from a tree that has a commercial value of £0 to £2 a cubic foot. It is interesting that for a maker, one tree might yield so much potential income.
Before you start rushing out booking onto my courses or just learning how to make fan birds, so you can make your fortune, there are a few things to remember. It is fine to make a whole batch of items but then you will need to sell them and that takes time and money. A certain amount of the stock can and will get damaged, especially with fan birds; and some will just fail as you make them – but that can be less with the more experience you have. Then there’s all the fixed costs: workshop rent, insurance, van, etc. And the value of the time that it takes.

I would be interested in how other people can add value to trees. Unfortunately it is not the grower who gets much money for the wood as our forestry industry is depressed. The green woodworker is not a great consumer of wood and can make a little go quite a long way. We also can use wood that would be considered fire wood, thereby adding value to it. However, a lot of foresters do not really want to sell odd bits of wood to the occasional green woody: they want to sell it by the lorry load.