Cheryl,
Have a look at the write up called "Threading On The Lathe- MACH3 Turn".
Don't know if it's still included in a MAch3 software download but you will find the latest in Memeber's Doc's. It cover's a lot about threading.
I am currently using V.062 along with a PP and all seems to work well so far,BUT,
must use at least a version greater than 3.043.33 and probably 3.042.38 would be better.
I use a Hall's Affect sensor, but an index wheel will work fine for the index for PP.
Note if your lathe has a "wimpy" motor then your threading may be limited in size
even when using some of the other cutting methods. The ability to do good threading will only
be as good as your total lathe "system" which also includes physical setup. Your pc should provide a good pulse, not much variation from Kernal speed ( the closer and more consistant the better ) as actual DRO rpm should not vary by much...say 1-2 rpm. The threading cycle provides for motor slowdown, but frankly, it's not the way to go.
If you don't use a PP then an external motion controller is need that supports threading.
Not up and the latest greatest so research before you buy. Post back for suggested boards.
Now since your just starting your project, strongly suggest, that the heart of your lathe,
namely the axis screws should not be junk and do it so there is no backlash.
Threading is not hit or miss if you do it right the first time and know before you go!
Seems someone has told me that before,
And I never listened
Slow learners we Lithvac's
RICH