Threading on Sherline lathe

I am trying to do threading on a Sherline lathe. Here is a list of my equipment.

2 Leadshine em 705 stepper controllers
1 Pmdx 122 Bob
Omron quad. Encoder and channels
Parport built in that does spp, epp, ECP
Dayton 2m139 spindle motor
Linuxcnc 2.7.8
2 AMT dual shaft 156 oz-in stepper motors.

First question is do I have everything I need or is a vfd needed?
If so what will work with this motor? It is 165 watts.

The lathe is trying to thread but it is still not synching correctly because I had set the program to do 4 tpi and it looked like 80 tpi. I will upload my Hal and ini files here today. My latency is like 19500 me if that helps. All help appreciated.

Yes the it increases by one on the halscope when I turn it by hand.

Not sure if it is able to do 4 tpi. For what I am doing I have to have 40 tpi internally and externally. I tried threading again, and I set the spindle speed at roughly 1000 rpm. The tool engaged engaged the part at the same speed it jogged to the part from the home position. It simply is not synching up to spindle.

Andy, I have just successfully made 40tpi work. Thanks for all the help. My problem was trying to use g76 instead of g33. So basically I was already there.
My slowest rpm is basically 1300 so I will have to change motors, so I believe I am good to go. You are a real trooper and I thank you for your help.