@ Solace,
the best and
"definitely" the "safest" way to drill "perfect" holes in thin based materials such as sheet metal and especially car body plastic is to use Step Drills such as these:
You will notice that each step on these drills is a different size getting larger the further you drill in.
They are available in either imperial "inch" or metric "mm". Metric being the most popular.
You can purchase them individually in different size ranges or as a twin or triple pack giving you a large range of sizes.
You can buy very expensive brands which are useful in the Engineering field or can just buy the general Handy-Man grade from "BUNNINGS" for approx $20 for twin pack. These will be more than adequate for drilling into the Rear Plastic Bumper.
Drilling Hint:
1) Place masking tape over the area you wish to drill your sensor holes, this will allow you to mark the right spot with a pencil or thin felt pen without causing damage to the paintwork.
2) Use a sharp pointy nail (press firmly) to centre mark the hole position.
3) Use a Cordless Drill with a small normal drill bit, approx 3mm first to spot and drill through.
4) Now use a Step-Drill and begin to drill slowly using the Cordless Drill on Slow Speed and don't press to hard. You can trigger on and off with your drill as you drill deeper and the hole increases in size.
When you reach the required size on the Step-Drill, stop drilling, remove the Step-Drill bit from the hole and your done. You should be left with a perfectly round and clean hole exactly where you wanted it.
Important: Do yourself a huge favour and buy the Step-Drill. You don't want to stuff-up drilling holes in your Bumper. You will always find many uses for it later. Money well spent.
Cheers:Sam
