First I must offer thanks to Wongo, the two Ians and a few others who taught me more than a little about wood movement and who corrected my evil woodworking ways.
I am one of those sick, twisted puppies who actually likes statistical analysis. So when I found some wood movement data published in a WW magazine I soon got it into an Excel spreadsheet and added the density data from Bootle. This wood movement data was uncommon because it is all measured data (by the CSIRO, from memory). What follows are some of my discoveries, most of which fall under the interesting but not necessarily useful category. However, some of you might find it interesting. First, here are the data.
Data.jpgOne of the early studies was to correlate tangential with radial movement. The outcome was interesting. The data formed two systems. A main system (shaded red in the next pic) and a secondary system (shaded in yellow). Hereafter these are called the red and yellow data. The yellow system is a set of timbers that show unexpectedly low radial movement compared to their tangential movement.
Tangential-Radial.jpgThe yellow woods were: rose she-oak; beach she-oak; northern silky oak; southern silky oak; black bean; Aust red cedar; river banksia and red banksia.
Then the data were correlated again in their separate colours, as seen in the next pic. The banksia’s are missing from the yellow tangential versus radial chart because they were a poor fit. They formed their own system where radial movement was exceptionally low.
Red.jpgThen Density was correlated with Tangential movement. For most woods density is a reasonable predictor of movement in the wood. This means timbers such as red and white cedar, cheesewood, celery top and black pine, all of which are low density, are low movement timbers. The eucalypts tend to move a lot more, because they are dense.
Yellow.jpgSo, I had fun (I know ... I am a sick puppy). What did become obvious was why celery top pine was so popular with boat builders. A firm timber with good strength that has low movement both tangentially and radially. This would have been especially useful for boats that were in and out of the water. The wetting and drying cycles would produce only low levels of movement. The same characteristic is handy for cabinetmakers in some circumstances.
Next time I am building a large table top or similar large panel, it might be instructive to consider a medium density timber with low expansion. This forum is chokka with examples of panels that have failed in some way because of wood movement. We can't eliminate wood movement, but we can, where appropriate, select timbers that minimise this movement and the potential attendant issues. Of course, we should always use construction methods that accommodate wood movement.
The banksia’s were interesting. They have average to high tangential expansion, but very low radial movement. If quarter cut, they would be a medium density timber with very low movement, and they are beautiful quarter cut. What a shame this wood is so rarely available.
Are there any biologists (or perhaps plantologists) out there who can shed further light on this subject?
Some of you are likely thinking I have too much time on my hands. That is correct. I am in Saudi Arabia, working. No clubs, no pubs, not even a glass of wine with dinner. No music, no singing and no dancing. I can go for days without seeing a woman, and when I do see one she is wearing a burka. What else am I going to do to keep myself out of mischief?
Have fun!
John
