Ballast Resistor & 24v Power supply

hi all,

picture below is my 3 axis cnc.

bought the controller board 3 years ago from hobbycnc. one lucky day on feb 2007 start building it and get it to finished one week later. i create my own CNC software with MS Excel 2003. i name it "ExcelMill". it was fun.

for the test, i create pcb for my spindle (on/off control). the result is acceptable for me. BUT it takes 45 minutes to do the tiny job. thats not ok for me (slow). i also tested with KCAM but the max speed is only 200 mmPM.

the board is 3ADBWOHC (old) from hobbycnc. design with 3 UCN5804B ic. the BALLAST RESISTOR is 2.7 ohm 10 watt (6 pcs). the motor is 80oz-in 6v , 1.2A. threaded pitch is 2mm. my POWER SUPPLY is ATX 12v 10 amp.

from the reading increse the input voltage will make stepper run faster.
so i decide to RUN it at 24V with 2 ATX power supply connect in series.

QUESTION:
1. Will it work if 2 ATX power supply connect in series to get 24v 10amp?
2. what value for the BALLAST RESISTOR for 24v input.

thanks.

http://www.excelcut.netmyne.com/images/cnc/dscn6124.jpg
http://www.excelcut.netmyne.com/images/cnc/dscn6127.jpg
http://www.excelcut.netmyne.com/images/cnc/dscn6145.jpg
http://www.excelcut.netmyne.com/images/cnc/dscn6149.jpg
http://www.excelcut.netmyne.com/images/cnc/dscn6150.jpg
http://www.excelcut.netmyne.com/images/cnc/dscn6154.jpg
http://www.excelcut.netmyne.com/images/cnc/dscn6155.jpg