The best gauge is the one that cuts the foam without breaking.

Mr Chips has realized the most important issue .....

This wire needs to be strait ... the longer the wire the more it sags . not just under gravity , but as the foam is pushed onto it horizontally ... The wire needs a heavy duty spring attached outside the cutting zone to keep tension ... as the current is applied the wire gets longer from expansion , and it gets less strong .... You need a wire which is very strong at around 500C .... stainless steel wire might be best , then you can have great tension in it to keep perfectly strait without it breaking.. Keep the temp as low as practical allowing high tension without breakage

Current and voltage are easily sorted , get a variable supply and experiment for the right temp .

 

Thank you for sharing. I found out that I need 2.6 A to heat up the wire till 420 Celcius, meaning I will need to have V=2.6x18 = 46.8 V to heat up the wire. The power needed in this case could be 130W. I'm planning to use a 48V 15A power supply, as I would also need to supply current to motors and drivers.

If it's not cost prohibitive, you might consider giving the cutting wire its own power supply, at least in the first rev of your project. Having a separate supply will reduce the odds that switching your big loads on and off will have any negative effect on your logic, which can make development faster and keep blood pressure lower.

 

@MisterBill2 Post #31 said:

I looked up the datasheet of the wire, and in the table, it states that it has to get 2.1 A for 316 C and 2.6 A for 417 C, I decided to go with the higher value, to maybe account for the cooling of the wire, due to its length. Is it a concern, can excessive temperature negatively affect the cutting process?

I don't know how accurate these numbers are. But if we go based on the information supplied by the Thread Starter (TS) we should be able to come up with an answer. Of course, the lack of information is a problem. OK, we have amperages and temperatures. But we still don't know what wire length or resistances. Hence, I'm not able to (or willing to) figure out the voltage supply for the wire length.

 

I used .03 " Ni-Cr wire on a 20 " bow applying about 20 lb. Power was from a Variac feeding a 24 V step down transformer. Current was reduced at the start of a cut & increased into the cut to a dull red, speed adjusted by feel.

 

A variac is a simple way. Remember to fuse the wiper on a variac.

Aside: Just and FYI though: I finally said enough of this old technology at work Phase angle fired temperature controllers w/current limit operated nto a variac with a custom 6 RU (Rack units) panel with voltage and current meters that didn't work (read the right values) anyway.

So, let's change to a 1.5 RU power supply. So, 12 RU of space was reduced to 4 RU for two heaters and no custom panel.
Wish the power supply (~40 V 20A if I remember ) read Watts.

We got significantly better heat lifetimes.

Just wished the power supply would read in Watts,

We also at one time used a 3 phase energy meter (about $1000 USD) to read the real power of Two or three 10-40V circuits,

 

For short wire around 6 in. used .004 Ni-Cr wire.
Stainless delaminated if over heated.
Just a guess, 2m of .03 -.045 might need about 100 lb. of tension when hot.

 

As I look at the list of "similar " threads it is clear thatvthe only commonality is the word "Huge" in the posted title. Is it possible that there is a better way of picking things that might be related? Or should there be some helpful information provided to help select post titles?

 

These guys are thought of as the got to guys for everything hot wire cutter, a lot of information even if you don't buy from them - http://www.jacobs-online.biz/nichrome/NichromeCalc.html