This looks to be what I want to build. I am confused about this tangential knife. The ones I have seen so far have been rather flat comparing to this knife. This looks like it’s almost 4" thick which is what I am aiming for. Also, does it go up and down? My google-fu is not working well today :(.
http://www.youtube.com/watch?v=kYBW9iWeWec
What thickness of foam are you looking to cut?
If it is up to about 100mm then something like a spiral saw might be ideal.
4" is what I am aiming for.
It’s a tangential knife. The blade moves up and down like a jig saw blade and it also rotates to keep the sharp edge of the blade facing the direction of travel.
Something like https://www.damencnc.com/en/tools/tangential-knife---accessories/tangential-knife
@Michael_Bridak_K6GTE Thank you for the info. Looks like I might have build this on my own since that site asks for $1500. 
What tool are good for cut foam ??
Sorry. Now i see the link 