Need for uniform thickness when rough turning

[Bernie Kopfer]

I frequently read about the importance of the walls and bottom of green turned bowls to be of uniform thickness; apparently to minimize cracking as the bowl dries, shrinks, and distorts.
Is this really the case? In my experience this has not seemed to be the case, lack of uniform thickness does not seem to lead to more cracking or to lessen distortion. I know what the books and "experts" say, but what has been your observed experience?

[Bill Howatt]

My experience is the same as yours - doesn't matter (much?).
I guess another part of the question could be "how uniform is uniform?". I tend to get the upper walls somewhat uniform but near the bottom and the bottom is definitely thicker in my roughing work.

[Edward Weber]

I'm in the same camp.
The wall and the bottom have different grain considerations due to their orientation.
Also, when turning to final thickness, I prefer to have the bottom third of the bowl, including the base, to be a little bit thicker than the wall. IMO this gives a better feel and stability for the bowl, especially if it's a utility type bowl.

[Richard Coers]

I consider it critical that all wall thickness and bowl bottoms must be the same. Species can make a difference. Try doing a green 14" bowl with a 1 1/2" thick bottom and the walls 7/8" thick in cherry and report back. How many large bowls have you turned green?

[Dave Fritz]

My experience supports what Richard said - it depends on the species and environment which the blank dries. Cherry, walnut and ash are pretty forgiving for me. Apple and white oak seems to crack if you look at it. All species aren't equal, nor are drying conditions.

[Peter Blair]

My experience is that if I am rough turning I have better luck if the piece as the same thickness throughout. To minimize cracking especially if the piece is going into my kiln to dry an as has been said different woods and even pieces cut from different areas of the tree can react differently. I would mention here as well, that again in my experience, when rough turning to final thickness it is very important to have a consistent thickness.

[Reed Gray]

Probably the most important part in rough turning twice turned bowls is to round over the rim. A sharp edge, besides being able to slice you, is more prone to cracking than one that has a 1/4 round profile. That sharp edge will dry more quickly than the rest, and that creates stress, and stress is relieved by cracking. You can leave the bottoms a bit thinner than the walls, mostly because it won't elongate as much as the walls will. Not sure how important that is.

robo hippy

[Neil Strong]

I make the rims as thick as they need to be for that particular wood to compensate for expected distortion during drying.

But, the difference in axial to radial/tangential distortion reduces towards the bottom of the bowl where the fibres become more sidegrain than endgrain through the cross-section of the wall there.

So, I green turn very close to final thickness towards the bottom of bowls.

I like to have thinner walls towards the bottom of my bowls and (mostly) thicker at the rims, where I can add some detail. I find those thicker rims sell well at the gallery. I learned that when I was a potter... the piece should feel lighter in the hand than it appears to the eye.

[Bernie Kopfer]

There has been some good advice given here based on turners experiences. it appears that cracking is not too much of a problem if the bottoms are a bit thinner than the walls. That has been my experience also, nor have I had problems when leaving the the bottom thicker by 25% or so. Richard feels that this would be a problem with larger diameter bowls and if that has been his experience it is worth noting. (But 7/8” walls on 14” diameter cherry is not close to the 10% rule and a recipe for disaster with probably any wood, Richard.) Gary’s observation about not leaving sharp rim edges is dead on.