Drilling a Larger Hole in Door for Larger Dead Bolt

I recently purchased a Schlage Camelot Keypad Deadbolt (BE365VCAM716) to replace my existing deadbolt. This deadbolt allows unlocking via a digital keypad. I decided to go this route versus a traditional deadbolt, a remote key fob, or biometric scanner for several reasons:

• I can gain access to my house without a key, as well as provide others with access such as dogsitters
• I don't have to provide a physical device (key, wireless key fob) to people to let them gain access, which is very handy if I'm stuck somewhere and need someone to access my house
  
• I no longer have to worry about who has a key to my house as I can change out user codes very easily
  

However, I ran into a dilemma - the hole in my metal door for my old deadbolt was smaller than the new one. The Schlage deadbolt requires a 2 1/8" hole, and mine was probably 1 3/4", or whatever the smaller standard size is. Drilling out a metal door with a hole saw bit is easy if it hasn't been drilled out before, but that wasn't my case. Thus, I had to figure out a way to get this larger hole drilled. My solution was to use the same hole saw bit to drill a hole through a piece of scrap wood, and then use that as a guide so that the hole saw bit does not run all over the place. This worked out perfectly and allowed me to cut through the door quickly. I had previously tried using styrofoam as a guide and just applying pressure to keep it there, but the bit was walking all over the place. Anyway, hopefully this helps someone out!