How big a knot before the pith is a problem?

[howlingbaboon]

Hi guys, I've been taking the advice I was given on here about avoiding the main pith when turning green wood. I've been either chopping it out first or turning the rims of bowls down to exclude it so far (face grain). I'm wondering now about knots and their pith. I'm sure there are no hard and fast rules with the vast variations between species, individual logs, dryness etc. Are there any tips you could give me as a beginner though regarding this. Do I need to try and exclude these as well? (I like the look of knots and would like to be able to keep them in if possible) Are there certain sizes that I'll be more likely to get away with (i.e. no cracks drying). My latest batch of logs are freshly felled Sycamore.

[fuzzyturns]

You pays your money, you takes your chance. It's a lottery.
In my experience it's mostly down to the rough turning. If you turn from green wood, try and achieve even wall thickness all over, and you have a half decent chance of it not cracking. However, if a knot (branch) is significantly large , i.e. more than 30% of the main trunk, you still have a physical problem with the shrinkage, and you'd need to rough turn to very thin walls to allow the wood to warp instead of cracking.  Which then means you have to finish the piece will green, because the warping will prevent any further turning once it's dry.
As I said, you pays your money, you takes your chance.

[Bryan Milham]

Fuzzy has fairly well nailed the answer.

But I'll add, avoid having the know in the rim, it will dry differently and cause warping and splitting issues.

If you keep it in the body of the bowl, it can be an attractive feature (and as long as you are happy for it) will warp and add a tactile effect to your work. Even if splits do occur while drying they can be filled to provide additional interest.

Les (Gwintog) posted a bowl/vase a few weeks back with just such an effect and this style of recovery is quite common in America, if you look through some of their club sites, you'll see many examples of cracks being filled with turquoise etc.