Good morning sir. Sorry for the delay. The first hammer i used before i built one had a very small gap between the blades and the outer wall. The batteries were getting torn and shredded into little pieces to the point that i had to have a magnetic belt to remove the fine pieces of shredded metal. You don't want to crush or shred the batteries, you just want to crack them. It was causing me a whole lot more work than i needed. Their are some instances where you want that affect, but this is not one of them. All we are really trying to do is get to the powder inside with the least amount of chemicals, work, or trouble involved. Sort of like cooking an egg! We want the yoke inside, but the shell is worthless to us. We only want the hammer mill blades to crack the batteries open so we can get access to the silver inside. Think of hitting an egg with a baseball bat! For this application i guess the clearance between the blades and the wall could be any distance that you want as long as it doesn't shred it into fine pieces and the machine still performs as required.
