We saw this bear proof bird feeder ( pictured below) at a house in Asheville yesterday:
It has for a number of years foiled the local bruins, coons, and squirrels.
Here is how it is constructed. The center pole is an 4" iron pole which formerly held a basketball goal. The pole is sheaved with an 8" stove pipe which sits on an 8" high and 1 foot diameter rock base. There is a sloping pipe collar (storm pipe collar) set on top of the rock footer. The added width of the stove pipe and slope prevents of the collar prevent the bears from getting a foot hold to start climbing the pole. The 8" stove pipe is telescoped over the 4" steel pipe, and at the top a second storm pipe collar is place for looks and to shed water. The 8"stove pipe is free standing and the combination of its smooth metal sides, and flexibility of the stove pipe prevent bears from being getting a firm claw hold on the pipe. With no paws able to attach to the pole the only thing left for the bear to do is jump the 10' plus up to the feeders.
The feeding stations are mounted on 4" PVC where 90 degree elbows, straight pipe, and pipe caps have been combined to make the mounting arms. The connection between the 4" steel pipe and the PVC station mounts is made by using a 4" threaded coupling which telescopes inside the 4" steel pipe. The pipe is painted balck.
The feeders have a large reservoir for feed, 2 gals. The owners choose to fill them using a ladder. He feels that a pulleys and rope system would be an Achelies heel to the system. They have a huge number and variety of birds.