If you do the drilling, use drills that are designed specifically for acrylic. Drill is commonly used twist drills, but you also need modification to avoid fracture. Modifications that you have to do is to grind into small flat cut both its banks there will be a little scar. Drill should be run with the correct speed then it will appear two continuous spiral ribbons from the hole.
Before you do your job better ensure the safety instructions of the equipment and materials used in acrylic sheet products. Materials used for acrylic sheet with a thickness of typically 1 / 4 "or 1 / 8".
When you do the drilling hold the work piece firmly or you can do with the clamp on the desk. You can back up with plywood on the bottom to prevent chipping. Make sure you drill up through the bottom surface. Let the bait a little out to prevent chipping to slow it down.
When you drill the acrylic sheet with a thickness of 1 / 4 "or more to use water as a cutting fluid which acts as a cooling water which will help reduce the heat and create holes with smooth walls.
The hole that has happened to you to force the screws or bolts to countersink. Thus, the zero will be soften countersink hole in acrylic sheet. You can also use a larger drill bit from the hole so it will produce a smoother hole.
You should note, if you want to cut acrylic should never attempt such a circle with a hand drill by pressing the acrylic sheet. This you do with a drill press to make the acrylic sheet in the machine-flops to the table safely.