I have a hot wire foam factory bow tool that cuts across a 48 inch panel pretty slick....I've seen a bunch of home made hot wire tools on youtube lately but not sure if there is one that long.....Have to look.....As far as clean and straight, I can't do it freehand....I have to put wood on the sides as guides for the wire to rest on as it cuts down through.....That's the best option I've found so far....ZR