cutting thru skim coat

[DonB]

I'm in the process of cutting an additional opening to engine bay thru my front (welded on) valance. I know under the paint is a skim coat and I'm asking for the best way to cut with minimal chipping to the finish. Shape is roughly as seen on after market Fiberglass offerings.

Options I see (in no ranked order) are:

pre-tape and cut thru the tape with cutting wheel on grinder (seemed to work well on drilling small trim holes.

perhaps first score with a shop knife?

First drill rounded corners?

Clamp a flexible guide as a straight edge?

My cheap air saw vibrates WAY tooo much!

Tips form my body experts?
Thanks
Don

[billymgb1000]

I would use the grinder with a cut off wheel and use the tape that will help too.

[Preform Resources]

X2 on the grinder, you can get a nice thin cutoff wheel 1/16" on a 90 or straight unit.
Dave

[DiDueColpi]

Hey Don,

I would tape off the area and mark off your finished opening size.
Then go back and mark off a slightly undersized opening, say 1/8th to 3/16ths smaller.
Use the smaller opening as your cut line and cut away with your grinder and 1/16th wheel.
Make sure that your wheel is rotating into the painted surface so that it won't lift the paint or filler.
Watch the tape for heat damage. If it bubbles or lifts slow down and let the area cool. The tape will show damage before the paint will.
Once the opening is cut, trim the remaining material with a die grinder or a hand file to your final dimension.
Once again file or grind into the paint so that you don't lift or chip it.
Remember to paint the exposed edge to seal it and stop lifting of your finish.

Live like you mean it.
Fred

[DonB]

Thanks guys.... Great tips.... just what I expected from the Pros!

Let the cutting begin!!!

Bones