use a cutting guide with your torch. best guide is one cut from 20 ga
steel, supported about 3/8" off the surface. A piece of 1/2" plywood
will do. Guide diameter is your rough out diameter minus the diameter of
the torch head. Clean up the worst of it with the grinder, chuck it in
the lathe. the first few passes aren't fun but it cleans up quickly.

I made a face plate and a chuck backing plate for my lathe out of 1"
stock this way. Takes more time to talk about it than just do it.

Jim Stewart wrote:
I have a piece of CRS, about a foot square
and 1" thick. I want to cut out 2 disks about
4" in diameter. I will ultimately turn and
finish them into flywheels.

Given my tools, here are my options:

1. Rough out the disk with the gas axe,
grind away kerf with angle grinder,
turn on lathe.

2. Mount plate on rotary table, taking small
passes mill out disk, finish on lathe.

3. Try to cut out disk with sabre saw,
finish on lathe. Painful just thinking
about it...

Any other options or suggestions?