Bowl jig

[RustyN]

Or can't swing one bigger than it rounds out over the bed.

True but you could go smaller. Here it is with the clamps for those asking.

[crokett™]

It's a standard woodworking jig.  Use something like the search criteria in my URL and you'll find all the ideas you need.  Fancy here Build a Bandsaw Circle Cutting Jig : 10 Steps (with Pictures) - Instructables where you slide in straight and swing round.  Mine's a piece of 1/4 ply base with the miter gauge strip and stop screwed on.

If you're just using it for the lathe, don't need to adjust the blade to pivot distance, just use your max radius to establish the pin.

ok. I see my mistake,  I did it so its clamped into place.  I'll have to modify it so it slides.  I have mine so I can index it in 1" increments up to a max of 12" which is the biggest my lathe can handle.