Okay, lets break down 2 Axis G Coding for a shaft nice and easy.
Picture you have an architectural pad with all the squares, the dead middle being home. Your Y code is simple as the will bring the carrage to the value you put in which would be 29- 30" The X moves your tool post in or out. You measure the taper you want at every 1". Divide that by 2 as you are cutting round. This means for each inch you give it a value divided by 2 until you hit your 29" (or 30").
Many have seen me running big to small. It is my understanding most like to go small to big so you start home 29 - 30 inches from home on the board and work inward, Each inch increment you give will leave an X. After you hit your 29 - 30 inches you will have that many X's, one per inch. You than connect with a line to each X. Depending on program you just hit G code and it does it for you. Save that file with a name and when ready open that file in the Mach 3 and your good to go.
You can buy cheap round wood at Home Depot to practice and check yourself before cutting precious wood.
This gives you UNLIMITED shaft tapers.
My offer is/was to take FEAR off the table. If you don't want to learn simple 2 Axis G Codes it would take longer for the computer to boot up than it would for me to G Code your increments and send them back to you.