This has been driving me crazy with this Ash tree wood. Notice the wall thickness in the picture where it’s thinner on the face grain and thicker on the end grain making the bowl look a little wonky. This was probably something in bowl turning 101 but… It doesn’t happen every time but did happen again the other day. 
I have been twice turning these bowls and on the second turn I do get a little tear out on the end grain and I’ve been starting with 60 grit to knock down some of that tear out ( with the lathe turning). My latest thought is that the end grain is harder than the face grain and that coarse of sandpaper is eating away at the face grain faster even though the bowl is spinning causing the wonkyness. 
Am I on the right track here? I’m thinking that on my next one, I’ll address the tear out areas separately with some 2” sanding discs with the lathe stationary, then move on with finer grits. I under stand its best not to have tear out but other than keeping my tool sharp and trying to alway do a supportive grain cut I’m not sure what else to do. 
thank you in advance for your advise. 

I've had that happen when I push the second turning before the piece is fully dry. The bowl "warps" as it dries and seems to get a little thinner at opposite sides. Especially true when I've started the second turning and get called away for a day or two.

You are correct about sanding and the end grain verses the face grain.

Thanks @HandyDan  and @lew for your help. I guess the best part about bowl turning is that I’m not wasting a money on lumber 😆 

 

There is another less obvious cause. When you remount the bowl the chuck must (unless you return the tenon also) grip the same spot as it did for the first. When you do the second turn you must return outside and inside. Bowl has warped as it dried and the choice is sand with warp or return inside and outside. I can say BTDT.

12 hours ago, Gerald said:

There is another less obvious cause. When you remount the bowl the chuck must (unless you return the tenon also) grip the same spot as it did for the first. When you do the second turn you must return outside and inside. Bowl has warped as it dried and the choice is sand with warp or return inside and outside. I can say BTDT.

Great point, Gerald!  I have been putting a witness mark on the bottom of my bowls when turning. That way I can align the bowl in exactly the same orientation if it needs to be removed from the chuck during the operations. 

I have little success trying to get tool marks out with the bowl turning, at any RPM. I work the trouble spots with an angle drill sander with the lathe off. The end grain is where you need the most sanding. By doing it with the lathe off, you focus on the areas that need sanding. I can't say the way I do it is the right way, it's just my experience.

When sanding with lathe off be careful to feather out the sanding or you could create a flat spot or depression. ZI sand lathe off but usually let the bowl free spin .

Getting rid of tear out is much easier to do with a bowl gouge than sanding. Sharpen your gouge. Turn the lathe up to what you are comfortable with, I turn up to around 1200 for finish cuts. Take very light cuts letting the wood come to the tool and not pushing the tool into the wood. Last and most important is ride the bevel. It will take a few times but eventually you will be able to turn without having tear out.

12 minutes ago, RustyFN said:

Getting rid of tear out is much easier to do with a bowl gouge than sanding. Sharpen your gouge. Turn the lathe up to what you are comfortable with, I turn up to around 1200 for finish cuts. Take very light cuts letting the wood come to the tool and not pushing the tool into the wood. Last and most important is ride the bevel. It will take a few times but eventually you will be able to turn without having tear out.

I’ve been practicing this technique a lot. Thanks