As stated before = make sure the meat is in grindable sized chunks, and cool the meat down overnight brfore you grind it. Makes a WORLD of difference.
I have a Hobart restraunt size mixer with the grinding attachment. We loaned it to a family member and it came back pretty much junk. It had set in a dirty, moist shed for 4-5 years, gathering rust. We loaneded it out in near perfect condition, and it came back in pretty poor condition. So - if you DO get a good grinder - don't loan it out!