Thanks for the reply,
Rough Shaping:
Final rough shaping involves truing up the block to 90° then cutting a 45° bevel each side and finally two 22.5° bevels each side on top and sides.
[url]http://i.imgur.com/9DUyTiT.jpg[/url]
Next (and this is the tricky part because it takes a bit of an eye for roundness) sanding off the excess in a controlled arc movement on the sanding belt.
[url]http://i.imgur.com/bdNKxBZ.jpg[/url]
[url]http://i.imgur.com/8vAqAXM.jpg[/url]
[url]http://i.imgur.com/W0ZiUMI.jpg[/url]
so the helmet has a slightly flattened ovoid shape in cross section.