I don’t think I’ll ever get around to changing my coal bin but I have bee thinking about ways it could be improved. When I built my bin I considered making the bottom like a hopper but I was in a hurry and didn’t want to make the job complicated.
Now, I have given it some thought and have some suggestions to consider. The angle of repose of bituminous blacksmithing coal is approximately 35º. Try making a conical pile steeper than that and it conflicts with Mother Nature. So, in order to help the coal slide to the door where I would like to collect it in my coal bucket the slope of the bottom needs to be just a bit more steep that 35º.
When I slide up the door I can easily reach a couple of feet inside in all directions. That’s where I’d like the coal to pile up. I don’t want it to slide all the way to the door because it would tend to just keep coming out.
The hopper bottom would have a volume of about 22.6 cubic feet. The original box capacity was about 64 cubic feet. The height of the box could be reduced about 8” and still preserve the 1+ ton capacity.
The leg height was determined to accommodate easy coal bucket filling. I could come down a few inches. If I kept the height of the legs the same and cut the box down 8” this hopper bottom would add 1’2” to the overall height. That would be too high for me to easily open the top as I do now and a little harder to use the top like a shelf. However the only reason I usually open the top is to rake coal closer to the chute opening which would no longer be needed. I don’t think it would complicate the once a year loading process.