Well the anvil I had has gone missing (looks in the neighbors direction ). So other then a section of rail track what would make a good anvil? "I" beam?
Do you mean that your anvil has been stolen? 24" of railway track standing on end makes a pretty good anvil for knifemaking. Having all that mass directly underneath the hammer is a good thing.
If you go the I-beam route the more mass the better so something in the 200-300 pounds per foot variety. Any bridges being tore down in your area? lots of scrap 1"-2" plate in a bridge girder
