I think I need to trim my hens beaks.

I have about 50 hens and at least half are pretty close to bald. I never really had an issue until I got a few chickens that were almost bald and ever since they seem to enjoy pecking each others feather out. I have them in a large coop and run, they get lots of fresh veggies and other treats. I was wondering if anyone had a good way to trim the beaks...I saw a debeaker/trimmer on Mcurray and wondered if it works. One other question how far do I trim it?