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How to drill hole in rear fender for light?

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How to drill hole in rear fender for light?

Old 02-12-17, 02:52 PM
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How to drill hole in rear fender for light?

Any suggestions for how to make a clean hole in my rear fender without messing things up (drill bit walking all over the place, etc.)? Anyone have a link on how to do this?
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Old 02-12-17, 02:59 PM
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Use a center punch (once you know exactly where you want the hole), then drill a pilot hole, and then enlarge it to size.

Oh, and use metal drill bits.

Guide to Making Holes in Sheet Metal - How to Work With Sheet Metal
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Old 02-12-17, 04:36 PM
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On very thin sheet metal, I use a reaming awl (like the one in a Swiss Army knife) to mark and start the hole. A punch could distort the fender.
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Old 02-12-17, 05:01 PM
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BITD every self respecting bike shop had a fender punch like this one.

Punching remains the best way because drilling a clean hole in thin sheet metal is near impossible. Without a punch you can drill a small hole then enlarge it with a tapered reamer, then file away the burrs on the back side. Or you can punch a hole with a hardened drift punch using a block or wood as the anvil.

I've also done the job using a self taping screw to start the process and finishing with a rat tail file.
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Old 02-12-17, 05:30 PM
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I drilled a hole for my tail-light in my rear rack, and I was lazy and did not take it off the bike. Despite covering my tire with a paper towel, the next day I got a flat from a tiny piece of shrapnel.

Don't let that happen to you.
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Old 02-12-17, 06:20 PM
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Thin materials I like to use a spring loaded automatic center punch for marking.

Center Punch - Automatic Center Punch with Brass Handle
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Old 02-12-17, 07:54 PM
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I have one of those fender hole punches! Actually have used it recently too. As to making well done holes- besides the center punching (or center pressing as with a plastic fender as a sharp scribe/poker/spoke does a good job of establishing a nub for the next step) making a pilot hole with a much smaller drill bit is a real good idea. First is that a small diameter drill will cut faster and with less wondering. Second is that any slight wonder can be corrected as one then uses larger and larger (till the end diameter is done) bits. Once the pilot hole is made the larger drillings can be just straight in if the hole is well located or the drill can be held at an angle to drift the larger hole one way or the other way. Very thin fender sheet can catch on the drill bit if not careful. A trick that can help is to sandwich the thin sheet between thicker sheets. In fact the outer one could already have the tiny pilot hole made to aid it's being lined up with your center punched nub. Of course doing any fender drilling is best done off the bike, or at least with the wheel/tire off the bike... Andy
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Old 02-12-17, 08:56 PM
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To add a small bit of information: flat cutting faces, such as those found on step-bits, have less tendency to grab sheet metal. They still cause a small amount of rolling on the opposite side of the tool, but it will be flattened by the washer/nut that clamps the light from the other side.
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