Freeware? Rhino has a free version which is a fully feature intense 3-D rendering program. a bit simpler perhaps is Google sketchup, but I dont know how truly accurate you can get with that in terms of angles, etc..
solidworks gets my vote but its $$$$!!
a frame is a simple enough drawing that with big paper, a big ruler and a big protractor, you can lay it out by hand in full scale. or get not as big supplies and do it half scale.