Since he cuts the wood with a chain saw, you likely need to run it through a surface planer before you even start to sand it. The progress up from 80, 220, 400...however smooth you want it.
If you aren't sure what a surface planer is, take a look at this one (there are many manufacturers out there - this is only an example):
http://www.woodcraft.com/family.aspx?FamilyID=7584
Claude