DELETING KEY SIGNATURES

Hello!

I am working on several octet arrangements. I want the parts themselves in the key of their instruments to NOT have key signatures and instead just use accidentals. I am able to delete the key signature from the score but not from the individual parts. I was able to do this when both the concert pitch button was on and off. I also tried dragging the key of C signature into the score but that didn't work either. I'd prefer no key signatures anywhere, but definitely no key signatures in the parts. Any idea what I can do?

THANK YOU!!! :D