I'd like to have a go at the scraping at some point and as such I'd like to start with making a straight edge. Commercial ones are much expensive for something to play with but I have a big chunk of cast iron bar, about 4 inches diameter and a couple foot long, I would imagine it's ductile. Is there any reason I couldn't turn this into a rough machined straight edge in anticipation? Make and screw a handle to it? Or is there good reason why they are cast the way they are and I'm breaking all the rules?