i started out with a sawzall, for the lower rough cut, then switched to an air nibbler to go over my measured cut.

 

The air nibbler works just fine...
That is what I used when I trimmed my fenders the last time....

 

i want to trim my fenders so i can fit 33's but i have no idea how to do it.

 

dremel and angle grinder.

 

I used tin snips and it came out pretty ugly. but the metal is ridiculously thin anyway.

 

Sawzall and angle grinder.

 

Grinder with a cut-off wheel, they have pretty good control and give good results

 

Like you and many others - I used a grinder and cut-off wheel then cleaned it up with a 120 flap wheel and really smoothed the edge with some 180 grit sandpaper. I can run my hand along it without worrying about cuts!

 

dremel tool, i was a stickler for keeping it clean edged

 

sawzall and a grinder

 

Masking tape and a whiz wheel....

 

Angle grinder with cut off wheel.

 

Wiss tin snips, cuts clean.

 

grinder with cut off wheel for me worked very well

 

beer and an axe....