Chopping a rear fender

[Psychopasta]

Hey Guzzisti,

I want to chop some length off the rear fender of my bike. What's the best way to do a good job of it and get a nice finish on the new edge?

- Pasta

[rodekyll]

What bike?

I'd try to preserve the edge by cutting the forward edge and rotating the fender, if possible.  Otherwise I'd cut it on a line and trim it with fender molding. 

[Orange Guzzi]

Install the fender, tie a marker to a string, hold one end at the center of the axle, swing an arc with the marker while making a mark on the fender side. Use the same length on each side to make it even.   This will give you a profile that matches the wheel. Decide a length for the back, blend the radius's to your liking.  Use the skill saw with a fine tooth blade to cut, finish edge. I used automotive trim over the edge on mine.  There are several choices.  Door edge trim, heavy u channel and thin rubber u channel.  I used the thin rubber u channel in black on silver paint.

[Psychopasta]

What bike?

V50 Monza

[Darren Williams]

Here is what I have done on quite a few occasions with painted metal fenders.

Mark the shape you want to cut on the fender. Tape off the saved part of the fender with vinyl electrical tape, several overlapping layers back up on the fender. This is like making a stick on template. Get a Dremel or equivalent with thin abrasive metal cutting blades and carefully begin cutting. Just score the fender next to the tape, and then repeat making the cut a  little deeper each time. Make sure you leave the edges of the fender to cut all the way through till last, as this will keep it in tact till the end.

Important, the reason I use the vinyl electrical tape it to gage heat. The abrasive wheel will generate heat and damage the paint. Go slow, very slow so the tape doesn't start to melt. That will prevent damaging the paint. Next use fine sand paper to smooth the cut edge being careful not to get onto the outer paint. Once smoothed, remove the tape and touchup the exposed metal edge from the cut with a similar paint.

[Guzzistajohn]

Here is what I have done on quite a few occasions with painted metal fenders.

Mark the shape you want to cut on the fender. Tape off the saved part of the fender with vinyl electrical tape, several overlapping layers back up on the fender. This is like making a stick on template. Get a Dremel or equivalent with thin abrasive metal cutting blades and carefully begin cutting. Just score the fender next to the tape, and then repeat making the cut a  little deeper each time. Make sure you leave the edges of the fender to cut all the way through till last, as this will keep it in tact till the end.

Important, the reason I use the vinyl electrical tape it to gage heat. The abrasive wheel will generate heat and damage the paint. Go slow, very slow so the tape doesn't start to melt. That will prevent damaging the paint. Next use fine sand paper to smooth the cut edge being careful not to get onto the outer paint. Once smoothed, remove the tape and touchup the exposed metal edge from the cut with a similar paint.

Good^^^ but with a pneumatic die grinder^^^

[Psychopasta]

Thanks for the replies guys, very helpful.

I would have thought a Dremel was the tool for the job, but GuzzistJohn suggests a pneumatic grinder and Orange Guzzi suggests a SkilSaw, which seem to me much more powerful and, erm, brutal. Am I just being a wuss?

- Pasta

[mrrick]

Thanks for the replies guys, very helpful.

I would have thought a Dremel was the tool for the job, but GuzzistJohn suggests a pneumatic grinder and Orange Guzzi suggests a SkilSaw, which seem to me much more powerful and, erm, brutal. Am I just being a wuss?

- Pasta

Yes.  Chain saw will save even more time.   

[rodekyll]

An abrasive wheel on an angle grinder or band saw would be my choice.  I wouldn't use a reciprocal saw like a jig saw or sawzall.  They're hard on sheet metal.

[Rough Edge racing]

 I have "bobbed" many fenders using a variety of tools over the years...As mentioned I would roll the fender forward and cut the leading edge if possible..This cutoff blade in an electric angle grinder does do the job...It does leave a burr and takes finesse to cut a slight curve as you cut around side edges..and an angle grinder in the hands of an inexperienced user will not leave a pretty cut...Practice on scrap metal of about the same thickness...A very fine blade in a sabre saw can also do the job and some may find it easier to make a nice cut...Again, practice..
 

[lucian]

Cut with tool of your choice a smidgen long of the line, make a wooden chalk to clamp fender in vise or down to a bench and hand file to the line. This will avoid overheating the metal and give you better control of the final finish of the edge.     Or chainsaw, I take it you don't ride in the rain. 

[Psychopasta]

Chainsaw it is, then!

[rodekyll]

Chainsaw it is, then!

If that's the weapon of choice, might I recommend a Stihl 030 of the same vintage as the fender.  I've slain many a tree with one, and the fender isn't any stronger than a Doug fir.