Kidbee,

that is one of those difficult to answer questions, it depends upon the starting point. If it's dried somewhat already (lost some of it's free water) it will apparently shrink less for you. Also the time of year it was felled, High summer growing season, it will be full of free water, midwinter, with the sap not rising much less free water.

Freshly felled 6.5% - 8% tangentially just over half that radially. If you are asking as a prelude to knowing how much to allow over to allow any shrinkage / warping that occurs during drying to be removed aim for 10% - 12%, but (and there is always a but...)

... that only works for evenly grained timber, if you are turning branchwood (tension or compression timber) I'd certainly leave it 15% thicker as a minimum as the drying will become more pear shaped than elliptical.

I don't know your Aussie timbers except through this forum, but Oak is a Ring Porous timber, if you have an equivalent type timber I'd suggest you work it similar.

I've some from a friend's garden I'm working at the moment, but they are to be smaller pieces, I'm taking them down to thin walls (5mm) and almost finished in one go. I rub it with Lemon Oil on the outside to slow the drying a little and so far it's holding it's shape well, but it has only been 4 days.