Thread: Expansion and contraction question

I think you may have something there. I had the opposite experience with the bowl in the attached picture. Unfortunately I only have the before pic and not after. I trashed the piece after about a week. It was my first turning attempt and the wood appeared reasonably dry but must not have been.

Within a day or two, it shrunk badly across the grain and huge vertical cracks opened up in the sides. After another few days the cracks closed up again but the bowl became completely oval and ugly - the amount of distortion was incredible. Originally it was about 6 inches diameter but ended up about 6 inches long by 5 inches wide.

Of course I realise that was due to my inexperience but it turned me off woodturning. At my age I don't have time to wait for timber to dry!

regards
Coldamus

There are several reasons why you haven't had problems,
using aged timber is likely to be one reason.

The particular species is another thing as some timbers don't move much anyway.

Also you will probably find that the finish you applied has sealed the timber sufficiently to prevent undue moisture variations within the timber so it's not moving enough to cause any problems.

Just as a matter of interest what finish did you use?

Originally Posted by Arron

All of this puzzles me.Is it because:
1. I've been lucky
2. The problems will come, they will just take a long time
2. e&c is a problem in some climates but not in suburban Sydney
3. the way we heat/cool (or dont heat/cool) and ventilate our houses means we dont have the characteristic problems of our Nthrn Hemisphere colleagues.
4. most cases of e&c are really misdiagnosed cases of continuing timber shrinkage through drying out. Most of my work is from recycled timber which has already been sitting in other people's houses for 50 years or so and so it is gauranteed dry.
Any thoughts. Anyone ever noticed problems in their own work through e&c ?
Arron

Arron,
The simple and truthful answer is "all of the above"!
Like you, on an early bit of panel construction, I glued those suckers right into a tight-fitting groove, intending to improve the structural strength of the cupboard I was making to withstand nuclear holocaust (or kids, which is a more severe test!).
Some time later, as I learned a bit more about the whole idea of frame and panel construction, I realised I had created a disaster in waiting. So I, too, held my breath for several years, but nothing untoward happened. As the piece passed out of my hands many years ago, I can't claim it's still holding up, and I rather think it isn't. The reason I think that, is it went to quite a different climate from where it was built, and the stresses on my poor construction were likely to be both different and more severe.

So why did I seem to get away with it in the first place?
These are my ideas, and I welcome any criticsm/further observations.
First, using a relatively soft and/or elastic wood that is close to average equilibrium moisture content (for the area it's in) is certainly going to help (my cupboard was mostly pine and spruce). Soft or elastic woods are going to be less likely to have to crack to relieve internal stresses.
Being at an average EMC when put together means smaller total movements for drier and wetter conditions.

You should get rid of any notion that wood dries to some mythical 'dryness' and stays that way. It's a hygroscopic material, meaning it takes up and gives off water according to the levels in the atmosphere. Surface finishes do not prevent this, they merely slow it down - some not by very much! Sudden and wide swings in humidity acting on freely porous surfaces are most likely to provoke disasters, but some expansion and contracion over time, is inevitable.....Aged wood is more likely to be at a fairly even moisture content, but this depends entirely where it's been!

Another factor is the glue you used - many of the 'modern' glues are relatively plastic compared with hide glue, particularly on warm days, and may allow enough give to ease stresses before any damage occurs.

Keeping our houses at more even temperature and humidity levels can't hurt, though it's unlikely you can prevent the wide swings we experience in much of Australia from Winter to Summer from occurring in the average house.

And finally - you could well be like the bloke who fell out of the 50-storey building. As he reached the 48th floor, he thought "Well, it hasn't hurt me so far......"
A few years ago, I repaired a family heirloom sideboard for a friend. It was made from Australian cedar about the turn of the (previous) century, and must have been the equivalent of chain-store furniture of the time. It was meant to look smart, but the carcase was nailed and glued up from solid sheets, cross-grain. The makers were well aware of what they were doing, I suspect, becuase they had used re-enforcing glue-blocks, and these were spaced across the panels so as to reduce stresses a bit. The pieces were only about 10mm thick, which also helped (less power developed as it tries to move). But move they did, and over a period of 50 years or so, it split in several places, then finally collapsed entirely as the glue gave way. I received it as a flat-pack.
I ended up making an internal frame and glued the exterior to that in a way that allowed seasonal movement. From the outside, it looked like the real thing, and all straight, square and useable again. The owner was delighted, but I guess I won't be around long enough to see if my solution is any better than the original!

Cheers,

made a bathroom vanity out of Tassie Oak which came from a local furniture maker & had spent a further 3 to 5 years under my house. Cabinet is tongue & groove (all orientated same way - sides & base). Whole thing has shrunk 2-3mm over 3 years in the bathroom!!
I had never accommodated e&C before - awful glad I did this time & I won't ever ignore it in future. Maybe it's the species.