I design and built a lot of my own tools.
I'm wondering if anyone with a larger lathe (say, 18 plus inch throw) and steady rest actually have used the steady rest at the full capacity. That is, if people with 18 - 24 inch inch lathes actually chuck up things that are 18-24 inches in diameter. I have seen people with large steady rests who were turning smaller things like a chalice. Maybe 4" in diameter.
I can imagine that with a long spindle that a steady may be needed. Maybe an aspect ration well over 5:1. But if a lathe only has a throw of, say, 40 inches or so, that having a steady capable of a swing of, say , 24 inches might be an over kill. If a person was concerned about flexing of a 24 inch diameter spindle, maybe the length would correspond to about 10 feet - - probably much more than most hobby turners work with.
So why am I wondering this? Well, it is important that a steady rest be both strong and stiff. So, if I design a stead with arms that are supported at a distance around 2 feet from an anchored point that they are a lot more flexible that shorter arms. Maybe 95% of most steady usage is with smaller diameter pieces - - say 8 or 9" in diameter ???
Am I missing something? When am I likely to need a steady over, say, 10 inches in diameter?