Hey, what speed controller are you using? Could you tell us exactly what equip you are using and how it is all connected?
It should be possible to get it dialed in. On my big mill I just set the vfd at 18000 and switch it on and off. On my little mill i have a grex, so i use the analog out and it works pretty well. I know that doesn't help , sorry, i have not used the serial control yet but we should be able to figure it out.
Chad