I see what you're saying Richard. My first thought was instead of building sloped sides out of wood and having all of that empty space in the bin I'd just have it filled with coal leaving a couple of ton unused. I could always shovel the coal into a mound on top of the auger the next time money gets tight. What you're saying makes sense though. I'll have to reconsider my plan before I buy coal. If (when) I put the sloped sides in the bin should the plywood be covered with sheet metal? If so, what should be used aluminum or galvanized? My brother in law is a sheet metal mechanic. He can get me material pretty cheap.
*censored*, I thought I was done.