Many vintage bikes have fenders, and often you find the fender tips in a mangled or misshapen state. These dark green Raleigh Dawn Tourist fenders are from about 1965 or so, and in need of some work. As they arrived, they needed some work. This is very typical of old Raleighs. The company used relatively thin sheet steel, and the fender bottoms tend to back on curbs and other obstructions.
As you can see the bottom has a bit out of the left lower tip. A clean up is in order, but the part is otherwise solid and can be worked into decent shape. The minor dings above the tip are hammered out gently with a ball peen hammer (more on that later).
The tip is the focus for today, as will be the tip of the rear fender, which is in somewhat better shape. Don't worry, you have plenty more to do once you've finished the shaping.
First, I look over what I have. It doesn't look bad, and most importantly the metal is solid. If the metal is all crumbly, then you may have to actually cut the fender up higher. Rust is OK, but the underlying structure of the steel has to be sound. This one is fine. I take a Dremel tool with a medium grade stone cone tip. It's the tan colored one here. I bring the Dremel up to medium speed and work right at the edge of the fender. The stone grinds down the edge slowly. Check the work often.
Once you have the profile you want for the tip, you'll probably have some slag peel on the edge and maybe some roughness. I next take medium grit sand paper (P320 here) and work down any uneven surfaces. You want to do this one without any drink in you- it's harder to sand a "moving fender". This time I am working BOTH on the edge and on the inside/outside. Work it slowly by hand until you have it the way you want. Don't worry at this point about removing all the rust- it's time now just to get the general shape of the fender tip the way you want it. In this case I want basically a stock arc. You could also do a custom shape, if you want something wilder (fork tail, Salvidor Dali blobs, whatever does it for you). I tend to like a stock arc the best for these (don't care for abstract art).
Here is the product- it's basically an even arc, and we didn't have to remove much metal because the steel was sound. I am willing to sacrifice perfect uniformity of the shape in order to save more metal. Some people just have to have a perfect shape, so will be more aggressive with the Dremel grinding. As you can see this arc is not 100% perfect (remember, working by hand is a little irregular itself), but once cleaned and painted to match the dark green, it will look nice. It's quite close, I think. I used a similar method to clean up a set of balloon tire fenders awhile back too.
I seem to have forgotten to add: you do NOT need a Dremel to do this. You can handle step 1 of the basic shaping using coarser sandpaper applied to the edge instead of a Dremel stone. It takes a little longer and is a little bit hard to work very small areas of the contour, but you can do it. The rest is the same as outlined above once you sandpaper your basic shape down. Remember though- you will need a relatively coarse sand paper if you have to remove much material. In the case above, I was removing maybe 1/16 of an inch to balance things out.