Here is a laser guided lathe tool modeled after one posted by Don Derry. This is good for making hollow forms with small openings and to a depth of 20 inches.
The tool bar is 24 inch long and 3/4 inch square stock. The laser holding bar is 3/4 inch square tube. The laser is held in some plumbing tube soldered together. The laser is a dollar store purchase keychain laser pointer.
I use two cutting tools. One is made from a 1/4 drill shank sharpened round on the end and flat on top and the second is made from an ice skate blade. Ice skate blades are made of very hard steel and hold a terrific edge - the material cannot be drilled with normal HS drills and holes have to ground through with silicon carbide.
The above photo shows the hollowing rig with the drill bit cutting tool in place. Inset shows the rig mounted on the lathe.
Above is a close up of the skate blade cutting tool mounted on the bar. I use the cutting tool above centre to avoid "dig in". This tool can be rotated to point in a variety of directions. The hole underneath is for the drill shank cutting tool.
And finally a note about drilling a pilot hole before starting the hollowing process. If you use a spade bit the bit will wander off centre and then it is hard to get the tool to cut properly without lots of vibration. So modify the drill bit as indicated in the following picture - this is called a spoon bit.
This grind on a spade bit will make the drill seek centre.