Drilling plexiglass must be done in a proper manner so that you avoid chipping or cracking. When drilling it you need to take your take and have a steady hand so that you achieve the desired result and that is a perfectly smooth hole.
Things you need
First of all you need to have some kind of lubricant prepared. The first thing that crosses my mind is oil but it could be a little messy. The better choice would definitely be water but mixed with baking soda so that it won’t cause a corrosion of the drill bit (baking soda is a rust inhibitor).
The next thing you need is a proper drill bit. You have the option of using acrylic drill bits, plexiglass drill bits, forstner drill bits (generally used with wood, but they provide a very clean hole with little or no chipping, require lubrication), standard woodboring drill bit (have a long centering point, don’t require lubrication) or carbide tip drill bits (goes through cleanly, requires lubrication). You can use a regular drill or a drill press (it provides much more control over the cutting speed), and additionally you will need spring clamps, masking or painting tape and a piece if scrap wood.
Place the plexiglass on a thick piece of scrap wood you don’t mind drilling into. Mark the location of your hole by using a simple permanent marker and then put a piece of the masking tape over the mark. The masking tape has the role of preventing the chipping once you start drilling into the plexiglass.
First: pilot hole
It is always good to start the work by drilling a pilot hole first. This hole needs to be drilled with a smaller drill bit and serve as a guide for the drill. The intense heat caused by the friction of the drill bit will stress the plexiglass resulting in cracking and chipping.
So while drilling the final hole use a spray bottle to lubricate the plexiglass with water mixed with baking soda during the drilling. Hold the drill steady under a 90 degree angle and please take it slow, do not push too hard. Once they start to surround the drill bit, you can stop and remove them to get a better view of what you are doing. If your plexiglass is thick, do peck drilling, going a little at the time so that you can remove the shavings from your hole and allow the drill time to cool. This will also help to prevent melting.
Basically this is an easy thing to do. Just get the right equipment, choose the proper drill bit, and please do not forget to put on safety glasses or goggles! You don’t what scrapes to catch in your eyes.