Lets Cut Some Stuff Up!
So, i get alot of requests on how i do these cutouts so clean. Figured its time to share the wealth!
First, here are the items i use to complete this proceedure
You'll need:
Jigsaw with fine tooth blade
Dremel with cut off disc and sanding drum
X-acto knife #11 blade
Sandpaper from 80-320grit
Some sort of flat plane items to use for sanding blocks (i used aluminum stock, the weight and rigidity make for fast level sanding)
And these, you can find at any art supply store
1ft (approximately) of 3mm mylar film paper
1/4 blueprinting tape (this is the best to use, because it is flexible, and has edging reinforcement that will hold a straight edge for big cuts) its available in many colors
First
Establish a center line in the bumper, this can be easily done by simply placing the tape in the middle of the plate area, and pulling it down over the bumper, and sealing it like so
Second
Here is where you can start trying out line cuts: starting the tape out on the centerline, you can pinpoint it with your finger, and the stretch it out to establish a straight line, once you have the length, slowly bring the tape down and then press with your other finger to seal the tape. Now you can work on the end curve by putting your finger on the starting point of where you want the curve to begin, and then slowly press it onto the bumper, following with your finger in the direction you want the tape to turn- basically, you are guiding the tape by drawing the line with your pointer finger.
Try different cuts before you decide
Third
Once you have decided on a cut line, we can now transfer over the curve to the adjacent side- This is where the mylar film comes into play.
Tape down the mylar over your curve, also fold over and tape down as many creases as you can- to keep an accurate transfer.
Now, Trace the curve with the draft tape
Follow your exact line
DONT FORGET to also trace the centerline so you know where to position the transfer once you flip it!
Here we have the flipped transfer, i lined it up by simply matching the traced centerline to the centerline on the bumper- Tape it down well on all angles, since you will be cutting it up- you dont want it to shift mid-cut!
Fourth
Now cut the centerline, this will give you a resting point once you start making the big main cuts
Simply start from one end- your choice: and cut away, following the line you made- Ive found the more streamline and quickly you cut, the better the cut comes out- going sluggishly tends to increase the waviness (its ok if its a bit' wavy, we can fix this later)
Notice the roughness of the cut, this is taken care of next!
Fifth
Now that we've cut, its time to clean up that jagged edge!
start with the heavy sandpaper and the largest/longest sanding block- run this back and forth in long streaks to level out the heavy waves on the cut, it could take a while to get it perfectly level- as your definition of perfection might be as high as mine. For the rounded edges, i switch to the smallest block (still with heavy sandpaper) and sand up and down the curve mixing with a horizontal movement (so, im sanding forward and back AND up and down simultaneously)- this will keep the curve true, but level the bumps.
Next you can use the smaller block with a mild sand paper to hit small trouble areas that just stand out a bit more after your heavy leveling work. Think of it as spot sanding
Finally, use the smallest block (choose something with a bit of flex; as this final step is only to smooth edging, not cut or remove) and something of 280-320 grit paper. Lightly sand the whole cut line to complete the leveling- and then angle the sanding block to smooth the edge (do this front and back to rid the bumper of any sharp or unsightly hardness)- This creates a "factory cut" finish.
Final Turnout
There you have it, a nice smooth and even cut with soft edges that look like it popped right out of the mold that way!
I'll note that this bumper im having painted to match my car soon- hence the roughness and sanding marks everywhere.
This bumper cut proceedure can be done on any bumper, without affecting the paint or condition (just look at the top pictures of my car, those 2 cuts were made without any markings or trace of damage)
As you'll see in the above pictures of my car, i have painted my under-structure black to hide the ugly shapes and chassis tinks. You may also wish to do this to have the cleanest look!
Depending of the depth of you cut into your bumper, some crash reinforcement might show-
For NB guys, just paint yours black like i did to hide it
For NA guys, your support is a little lower down, you can simply cut the lower portion off with the jigsaw since it is plastic
Or remove that junk completely- i don't recommend that.
Good luck!