Posts: 1663
Location: Kodiak, AK | It helps relieve stress after you drill the hole. There'll be an unfinished surface left, and that unfinished surface is prone to generating stress cracks. When you chamfer that edge, you're removing all the tiny jagged edges and evening the surface so the stress is more even distributed, and hopfully stress cracks and even larger full-on gell coat cracks are minimized. (Stress is concentrated at corners, cracks and jagged edges.) Just like after you cut a piece of sheet metal, you file the burr off; the burr concentrates stress and can lead to metal fatigue and a crack.
You don't have to get fancy with it. You're just removing the "burr" left from drilling the hole. I use a drill bit two or three sizes larger and do it by hand. |
