off center turning

I suggest you search for a book on the subject or at least a book that includes offset woodturning. Spindle turning is pretty simple, but bowls are a lot more complicated as you need counterweights to keep the turning balanced and also to keep your lathe from walking out the door. There are offset chucks available from various suppliers and you can also make your own, but it will save you a lot of grief to research on the net before you try anything heavy. A good intro to offset turning without the risk is to try some bark edge bowls. That kind of turning has a similar feel to offset, but it’s much safer and easier because the workpiece will be balanced. In case you are not familiar with bark edge turning, you mount a log with the bark on crossways on a faceplate or with a pin chuck right in the center of the log. If you use small faceplate you will have to flatten and area in the center of the log, and if a pin chuck, then drill a hole for it. The chuck is mounted on the top of the bowl to allow you to turn the bottom first, make a tenon or a hole for your chuck and then reverse it to do the hollowing. You will be cutting air for the most part, so it’s important to keep your gouge steady working your way out from the inside and cutting towards the center as you would with a face grain turning. Other than that there are probably a lot of Youtube videos on the subject. Have fun and stay safe.

As Mike questioned, are you referring to spindle turning or face plate turning?
Here is a link to an avid turner and jig maker- Mr. David Reed Smith
http://www.davidreedsmith.com/Articles/OffsetTurning.pdf

For offset face plate turning, try Ruth Niles at http://nilesbottlestoppers.com/Pendant-chucks.html