Thanks PB comments like that are always welcome.
Lets comment on the senario..
Firstly, sliding patio doors similar to the one in the photos above are the main method of break-ins to peoples property.
I would have , on average 5/6 calls per week in the Wicklow / Blessington area to replace the cylinders on such doors.
From the photo above, it looks like one of the older sliders. If this is the case and the op damages the internal mechanism by snapping using a vice grips she wont be able to get a new one.
If when snapping, the cam falls into the lock case (as often happens) what then? (Incidently the snapping using a vice grips is called the Bulgarian Technique)
Should the op decide to drill, the points to consider are
1. Type of Drill bit
2. Size of drill bit
3. Where to drill
4. When to stop drilling
5. What to do after drilling
6. What happens if the drill bit breaks in the lock.
7. Be careful that the bit does not bounce accross the door and break the glass.
Alternatively, call a local locksmith, get a couple of quotes - pay no more than 75 euro to include a new cylinder with 3 keys.
Paddybloggit is this any help? .......If a leg breaks go to the doctor, If a tooth breaks go to a dentist....... If a lock breaks..........