The heaviest dutiest is not portable! Look for a Singer 15-91. This was the best advice I ever got. They are out there and not expensive- I found one locally in a nice cabinet for $60. (a 1953) Check out the vintage machine shop thread here and see what advice you find. I think that the old Featherweights, up until about '61 were all metal, but they are still 3/4 machines.