Cutting of cast iron differs greatly from cutting steel for example
Much greater preheat is required Cutting nozzle is oscillated constantly across the cut (much like a weave bead) Oxygen pressure is 25 to 100 % greater Flame must have an excess of acetelyne
Preheat the full depth of the edge where the cut will be started. By preheating this part of the casting the cut will start quicker and much more easily.
Incline the nozzle at 75deg away from the edge to be cut. The inner cone should be 1/8" to 1/4" above the surface. Start the torch oscillation on the starting point, when the metal begins to boil start the cutting oxygen flow to for an instant to blow off the slag. Move the cutting nozzle just off the heated edge, open the cutting valve quickly and then begin cutting.
The cutting will be done with the torch at a 45deg angle and with a weaving motion from side to side, as the cut progresses gradually strighten the torch up to a 75deg angle (always pointed backward).
If the cut is lost at any point restart as described above.
Cutting of Stainless steel
Injector type torch is is supposed to be used 50 to 100% more heat required than plain carbon steel Oxygen pressure 15-20% greater than carbon steel Cutting progresses in the vertical down motion, during cutting the torched is oscillated with an up and down motion. Torch is adjusted to have a very slight excess of acetelene. Hold tip approximately 3/16" from surface
To start the cut place the part so that the edge to be started is parallel to the ground and the cut can progress downward. Preheat the depth of material where the cut is to be started, when the line of the cut is preheated to a dull red concentrate the heat at the cutting start point. When the cutting start point becomes white proceed with the cut.
Two other methods are also described in this publication, one involves adding a steel rod to the cutting path, similat to TIG welding , the other is to make use of sacrificial plates on either side of the stainless.
Have fun experimenting