If your trying to process mashed and mangled copper/aluminum coils I think it was alloy2 that had said use a hammer mill of some sort. if your trying to run bales or really big stuff and your mill isn't big enough than get a pre shredder that can handle the initial drop and then throw in what pieces your hammer mill will accept. for example if you get a mill from mt. baker mining and metal you may need a shredder to run anything bigger than 6 pounds productively.