There are just a few general principles that must be understood to successfully drill acrylic:
– DO NOT use a standard wood or metal cutting drill bit. You will risk cracking and chipping the material. These bits will pull into the material and will bind as they exit, cracking and chipping. Successful holes have been drilled with a standard bit, but the risk is extremely high. LP Aero Plastics Acrylic Drill Bits have been reground to have a 0 degree rake on the cutting edges. They scrape a hole instead of cutting, and will not bind or pull upon exiting the material. If for any reason you elect to use other drill bits, be sure to modify the bit so that the cutting edges have a 0 degree rake angle.
– DO use very light pressure when drilling with acrylic drill bits. It is possible to crack or chip the material by forcing the bit with too much pressure. For instance, when drilling a vertical hole, the weight of the drill is all the pressure that is needed. Be patient and give the bit time to do its work. You should see just fuzz coming from the bit – if the bit is pulling spirals from the material, you are using too much pressure. Use higher drill speeds on small hole sizes, and slower speeds as the hole size is increased.
– DO drill oversize holes. Acrylic will expand and contract at different rates than the airframe, so oversize fastener holes are required to allow for movement. The general rule is drill a hole at least one and one-third the diameter of the fastener.
– DO drill larger holes by step-drilling starting with a smaller size bit. About the largest size hole you can drill easily in one step is 1/4 inch.
– DO use a countersink to chamfer the shoulders of all holes. Any sharp edge tends to be a stress riser, so break all sharp edges. This also applies for all window edges. You can use a sanding block and a fine sandpaper (150 grit or finer) to finish the window edges.
– DO practice on the old window or a scrap piece of acrylic material.
Drilling, trimming for fit, and fastening acrylic windshields and windows is not difficult, you just have to understand the material, the tools required, and the proper methods. With a little practice and a little time to get the feel of the processes, you will have a very satisfactory installation with a long service life.
STORAGE: DO NOT ALLOW THE WINDSHIELD OR WINDOW TO BE EXPOSED TO SUNLIGHT WITH THE PROTECTIVE COVER APPLIED. EVEN SHORT EXPOSURE WILL MAKE THE COVERING VERY DIFFICULT, IF NOT IMPOSSIBLE, TO REMOVE.