tool for the job is just common sense. Some times the right tool will only be needed once. thats where the skin meets the cat. you can be an 8 year old in grade school art class or a historical artifact restorer and use the same tool or the same method. Nowdays there are templates in art stores that can help or you can take the time invest in some really exotic wood and find some really decent brass stock and make one. Here is an article about a do nothing thing a ma bob or an exacting elipse machine.
http://americanhistory.si.edu/blog/ellipsographsThe swamp fox article at the bottom is a quick interesting read also.