Does anyone have plans for a gravity bin feeder that is plywood?  I have been using a galvanized feeder, but the food does not slide down to the openings at the bottom.  I want to have separate chutes to put grains, grit, and calcium on the side and not mixed in with the pelleted food.  I think it would be a neat idea to have it accessed from the outside with just the area where the feed is available to the chickens on the inside of the coop.  We have cold winters and don't really want to open the big door very often. 

I guess my main question is how much of angle should I aim for for the food to slide down on its own, without getting stuck.  I see a few pictures on the web, but there are not any plans with measurements.  The angle is pretty important for the food to dispense properly or I will have the same problem with the feeder that is supposed to fix several times pushing the food down.

Thanks for your suggestions!