Mechanical shakers are what I usually see on sifters. The flow-throughs usually have a blade or knife that is pulled along the bottom with a winch and cable to cut/loosen/remove the castings clumped. Rarely do I see a photo of this blade.

Good luck!

Blade? Knife? Well, a bar of some sort.

would love to see the mechanism.

https://www.youtube.com/watch?v=tu3Blx4uQfw

This is a one in action but does not show what its doing.

That may be the best view you are going to get. The bin is a Work Wigwam large scale bin, the same system used by Worm Power. Maybe that will give you something to search on.

Great info Thank you had not found that one yet, lead me to another one. "The worm guy " probably the most informative i have found, on operating a 1 man commercial worm farm.

http://www.redwormcomposting.com/videos/worm-guy-mark-yelkin/