Yes you can include the pith

[Don Wattenhofer]

I have been trying to turn some pieces of black cherry before they are to far gone. One of my pet peeves is many turners seam to think that you have to dry the wood before turning and then they complain about all of the cracks that inevitably develop. The basics of the effects of drying wood is the shrinkage coupled with stress in the wood. The problem with drying a bowl blank is that the moisture can only escape from the exposed surfaces and end grain will give up moisture the fastest and cause checking in those areas. The large mass in a blank effectively seals in the moisture and if it ever does dry the radial and tangential shrinkage will cause major cracks. The one method that works is to rough turn to a uniform thickness which provides more surface area for the moisture to escape and allows distortion to relieve the effects of shrinkage. The second method is to turn to a very thin wall and live with the distortion.

This photo shows a black cherry bowl from a crotch with the bottom or main pith facing and you can see the cracks that were there before I started turning.

This photo shows the top with 2 main piths and 1 smaller pith but no cracks.
The photos do not show it clearly but all 3 of the major piths bulge out and the sap wood between the piths is uneven. The small shallow bowl on to is a loss since it distorted so badly on it's bass but I had to try.
The bowl was turned t a relatively uniform wall thickness of .09" to.04" then sanded with Abrnet all before it dried

 

[hockenbery]

Yes you can.

As you point out the tangential shrinkage is larger than the radial shrinkage, so each growth ring shrinks more than the one inside it.
In thin walled turnings the inside growth ring can be pushed out as the outer growth ring shrinks. In thick walled pieces a radial crack usually occurs as the outer growth rings shrink.

Small endgrain turnings with a natural edge - goblets, vases all have the pith in. These tend to have the curve of the bottom near the pith allowing it to bulge out without overly distorting the form. These will have a stem that should not include the pith because of its structural weakness.
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NIP pieces showing the ring of knots have the pith in. NIP has a hollow pith which reduces the stress

Every once in a while I turn NE bowls with the pith in. The pith dries as a bump which compromises the curve of the bowl. When other features of the bowl out weight then negative feeling I get towards the bumps I leave the pith in.

This was a small log I turned with the pith in to get a taller bowl
Pith pop out ruining the curve

 

[john lucas]

There is a lot to learn about working green wood. Yes you can leave the pith in. If you slow down the drying enough it usually will not crack. I've done it by putting the pieces in a plastic bag and turning the bag inside out every day. That's a slow process and can sometimes lead to mold but it does work. As an experiment I dried a 2" thick slice off of a 20" maple log. Those will almost certainly crack. this one I sealed both sides with anchorseal and left it in the shop away from direct heat of sun. It dried crack free in about 3 years. If you place the pith in an area that is cupped shaped or cone shaped and is thin the cup will get taller and narrower but since it allowed the pith to move it is less likely to crack. Learned that trick from Dave Barriger. Turn it thin. 1/4" or less and then bag it for a few weeks. Again this slows down the drying and because the wood is thin the pith can warp and may not crack. There is so much more to be learned and I'm sure others will expound on green turning. Just for fun I dried a blank big enough for a cowboy hat by covering it with stretch wrap. Don't remember exactly when I did that but it was about 5 years ago or so. It is dry enough to turn but may not be totally dry, I haven't weighted it in a while. Anyway you do it, slow drying is the key. Oh another tip I learned. After you turn the outside on a hollow vessel cover it with stretch wrap while you turn the inside. I used to have a lot of cracking because the outside was drying and shrinking and the inside was still wet. the stretch wrap stops the outside from drying.

 

[Don Wattenhofer]

Yes you can.

As you point out the tangential shrinkage is larger than the radial shrinkage, so each growth ring shrinks more than the one inside it.
In thin walled turnings the inside growth ring can be pushed out as the outer growth ring shrinks. In thick walled pieces a radial crack usually occurs as the outer growth rings shrink.

Small endgrain turnings with a natural edge - goblets, vases all have the pith in. These tend to have the curve of the bottom near the pith allowing it to bulge out without overly distorting the form. These will have a stem that should not include the pith because of its structural weakness.
View attachment 31025. View attachment 31028 View attachment 31026

NIP pieces showing the ring of knots have the pith in. NIP has a hollow pith which reduces the stress

Every once in a while I turn NE bowls with the pith in. The pith dries as a bump which compromises the curve of the bowl. When other features of the bowl out weight then negative feeling I get towards the bumps I leave the pith in.

This was a small log I turned with the pith in to get a taller bowl
View attachment 31024 Pith pop out ruining the curveView attachment 31027

Ditto all you said about goblets especially the point about not having the pith in the stem although I once did an ash goblet (hollow pith) from the main trunk of a 4" diameter tree that was one of those rare trees with the pith centered. I was able to run a wire from the cup and out base so obviously it would not hold water.

This goblet is made from Black cherry with a wall thickness of about .03" and while it does not show in this picture the bark shrinks less than the wood giving a rippled look to the edge.

 

[Don Wattenhofer]

There is a lot to learn about working green wood. Yes you can leave the pith in. If you slow down the drying enough it usually will not crack. I've done it by putting the pieces in a plastic bag and turning the bag inside out every day. That's a slow process and can sometimes lead to mold but it does work. As an experiment I dried a 2" thick slice off of a 20" maple log. Those will almost certainly crack. this one I sealed both sides with anchorseal and left it in the shop away from direct heat of sun. It dried crack free in about 3 years. If you place the pith in an area that is cupped shaped or cone shaped and is thin the cup will get taller and narrower but since it allowed the pith to move it is less likely to crack. Learned that trick from Dave Barriger. Turn it thin. 1/4" or less and then bag it for a few weeks. Again this slows down the drying and because the wood is thin the pith can warp and may not crack. There is so much more to be learned and I'm sure others will expound on green turning. Just for fun I dried a blank big enough for a cowboy hat by covering it with stretch wrap. Don't remember exactly when I did that but it was about 5 years ago or so. It is dry enough to turn but may not be totally dry, I haven't weighted it in a while. Anyway you do it, slow drying is the key. Oh another tip I learned. After you turn the outside on a hollow vessel cover it with stretch wrap while you turn the inside. I used to have a lot of cracking because the outside was drying and shrinking and the inside was still wet. the stretch wrap stops the outside from drying.

The bowl that I started this thread with was dry in less than a days time and nothing was done to slow it down.