that i do recommend..just never seen one small enough for a circular saw.
again use the proper blade...tuning a wood one around is just asking for damage to yourself.
reciprocating saw
good bi-metal blades
eye protection
I have never seen a circular saw blade designed for metal. Ask at your local hardware store if they do. A blade designed for wood WILL tear the metal instead of cutting and may also hurt YOU. I would suggest a grinder and a good wheel...