DRILLING SHEET METAL
How do you easily drill sheet metal?
Many of the sheet metal products we sell are supplied without holes. Where there might be several ways of mounting an item best leave it to the customer to decide. The most common of these item would be fenders. Mudguards where pre-drilled on factory bikes and select fitted on the assembly track. Some fit well while others did not. If a half way suitable guard was found that last hole may have been made to align with an awl. That is why some factory bikes had cracked fenders while others did not. You would find this problem most commonly on aluminium fenders.
Below we have demonstrated the recommended procedure for mounting a fender:
It is preferable to drill fenders before they are painted or plated. That way you can be less concerned about damaging the finish. Begin by mocking up the guard with the stays and braces. Some wood blocks or stuffer material (shop rags, etc.) between the inside of the guard and the tyre will be helpful but not essential. Once the fender and stays are positioned, as you like, mark the hole positions with a scribe or felt pen.
Next use a center punch or awl to dimple the fender at the center of each mark. Hold the punch steady and strike lightly with a small hammer.
The dimples you have punched will help locate the drill bit and prevent it from walking across the surface. Drill a small pilot hole in the center of each of the dimples. I find a hand crank operated drill works best as if offers the most control. A drill motor on low speed works too. Caution should be taken as a drill can be pulled through the metal and into something you did not intend to drill (like the tyre).
Finally select a drill bit which will allow correct size the bolt to pass through. Too large a bit can allow the fender to move around and crack. I prefer to use a step drill bit. They make quick work of drilling sheet metal. Also the hole they make are clean and not distorted. This is where a hand crank drill is handy. A power drill and standard bit can easily be pulled through sheet metal. You can lose control and damage the fender. Step drills have built in stops which prevent over drilling.
Now fit the bolts.