How to Metalshape a Custom Fender

You'd be surprised how simple it is to shape a simple custom fender with hand tools (and some shop-made tools). Don't believe me? Check out how we did it in this video!

You could use either steel or aluminum for this project. Steel thickness ideally 1.0mm. Any thicker and it will be hard to hammer. Aluminum thickness can be 1.6mm and still workable.

You need to measure up “roughly” how much metal you need. In the case of this fender, we just wrapped a tape over the tyre to estimate the size of the blank at 5” x 18”. Leave around ½” or 12mm all the way around that you can trim off to the exact profile as the last step.

If you’re using aluminum, you might need to “anneal” or soften the metal to make it easier to work. This is done by dusting the surface with soot from an acetylene torch, then evenly heating the sheet until all the soot is burned off. The temperature the soot burns off is an indication of the tempering temperature. Let it cool slowly in the air. Then you’re ready for the next step.

• A heavy mallet (the red one is 3 lbs)
• Sandbag, approximately 350mm (14”) diameter
• Wooden shrinking bowl
• Tucking fork (make from a pair of pin punches)
• Bowl or panel dolly
• Slapping spoon (make one from an old file)
• Metalworking file
• Sand paper (the white paper I use is Aluminium Oxide)

Strike the metal hard along the centre of the fender. This will stretch the metal as it is forced into the bag, cause the metal to curl. Straighten the fender out by hand as you work. Continue until you have a rough profile established, and the edges are wavy.

Continue dishing the length of the fender. Now we are working either side of the centreline of the fender.

Straighten the fender by pushing down on the ends. This will help pull the sides in.

Switch between hammering and straightening until the profile is essentially the final shape, even if it is rather lumpy!

Since the metal has moved from a straight blank into a compound curved shape, the long edges of the fender are now too long and will wave and fold. Use the mallet on a hard surface (curved/dished wooden bowl works well). Hammer out the tucks. Try working from the point of the tuck back out to the edge and “trap” the tuck.

Continue shrinking the tucks and smoothing the fender in the wooden bowl

If you want some more crown in the panel, shrink the edges again. Use tucking forks to make short tucks along the edge.

Hammer those tucks out in the same fashion as before.

With a slapping spoon (in this case, an old file bent into shape), and a dolly (we used a post dolly in the vice), tap out the lumpy surface.

This will take a while! But is the best way to proceed if you don’t have access to an English Wheel. Run your hand over the surface: you’ll feel any uneven areas. Keep planishing….more….you haven’t finished yet….keep going…!

If you do have access to an English wheel, then its possible to speed up the smoothing operations. Select a lower wheel that matches the profile of the fender. Use light clamping pressure (perhaps have the wheels just touching) and wheel the part. You’ll feel the lumps rolling out. When it feels smooth, you can increase the clamping pressure between the wheels and smooth it out even further.

Using a normal metalworking file, smooth out the crown of the fender. The file will hit the high spots. Keep filing until the high spots are brought down to match the low spots. Take care to not put any flat spots in the fender with the file. Sweep it over the crown in different directions to prevent flat spots.

To go to the next level, smooth out the surface perfectly with a sander. A dual action is best but this old 1/3 sheet sander did the job just fine.

The surface should be perfect at this point. No filler would be needed if you were going to paint the fender.

Right!

Now it’s up to you!

You have to try it!

You won’t learn from sitting here reading about it!