Homemade Framing

I'm trying to re-use an old set of matts but they need to be re-cut to fit the size of the new picture.  I've tried to do this job years ago and failed.  I'm hoping this time it'll work out differently.    
     Its darn hard work and I'm not surprised by the costs of professionally done frames.  Of course, those pros would have the specialized tools I can only imagine.