Wanted to ask,
If i use a servo tester with a turnigy 20A esc connected to a 3S batt will this work?
Also seeing i need 12V but ESC is 3S so will only get 11.1V is this enough? or i need to boost power to 12V for it to work smoothly?
The testers dial needs to be near low to keep amps low right or it could melt the foam fast right?

No need of exact 12v....11.1V is OK...

You are right about the tester dial....

Dial low -> Low amps -> less heat -> slow melting of foam

Thanks a lot santosh , just wanted to clarify.

Hey guys 
posting after a long time....
just improved my previous hot wire cutter making it more portable..

Items Used:
Guitar thinnest string
2 elbow
1m pvc pipe
some wires
Brushed ESC
1300 mah battery
and using it through tx/rx

Enjoy 
Yash

well... well.... well..... a CNC hot wire cutting maching.  For once we need to think about the cost involved and the product produced.... if you are mass producing... go and set up a cnc machine. OR ELSE.............
1.   Take a 4 feet bamboo pole and get it split into three pieces (length wise)
2.   Make a bow out of it... something used for shootin arrows. Fix the bow string made of E string of a guitar or the control line wire used for control line models.
3.   Take a 12 volt transformer.... house hold 12 volt adapter used for various appliance.... take two normal copper wires out of the output of the adapter.
4.   Fix aligator clamps to the ends of each wire.
5.   Fix the aligator clamps to the bow string (each ends of it) and wait for a couple of minutes for the wire to heat.
6.   Your hot wire bow is ready for use... use it by holding the bamboo bow to pull the hot wire across the foam. Use aerofoil templates fixed at the end of the wing planform of the foam to run the hot wire around them for getting the desired shape. DO NOT FORGET TO PUT WEIGHTS on the foam to keep it steady (for weights I use pieces of marble stone cut into 2 - 3 inch width and 6-8 inche length and about .5 - 1 inch thick.. (can but it from any construction material shop which sells marble or any other such stone.  They actually cost nothing).

The 12 Volt adapter gives 12 V DC (direct current).  For heaven's sake never mess with the commercial elecrtical home supply of 220 V and 5 - 15 amps.... it might blow the fuse or hurt you terribly requiring hospital admission for burns.

Using this setup you will not spoil your costly lippo or the esc.... use them for flying and use other low cost items which are readily avaiable for other jobs.

Happy cutting your foam..... Happy Flying