What's the best way to cut fiberglass for an exhaust cutout?

[rennch]

I have my RS Rear bumper now, but it's not cut out. How should I trim it?

[Early_S_Man]

Cutoff wheel on arbor in Dremel tool or die grinder ... same method was used by Mark Donohue to make slight 'adjustments' to front splitter of 917/10 at the track in 1972!

[rennch]

Ah...the ol' dremel. Well, I have one of those at the ready. Thanks!

[billyboy]

pneumatic body panel saw followed by a sander.

[rennch]

I don't have a pneumatic body panel saw. I have air tools...and a sabre saw. Would that work?

[billyboy]

just use a very fine blade that is sharp. you don't want to make alot of heat.

[rennch]

So, I can use my saber saw then? What blade do you recommend? I can go pick one up...

[Jeff Alton]

Dremel with a spiral bit on it. Like a hot knife through butter and makes corners very easy.

Cheers

[rennch]

Jeff...Is the spiral bit conical shaped? I want to make sure I get the right one.

[look 171]

large hole saw. then follow with jig saw. Use plastic down cut blade. sand or file to finish.

[rennch]

Well, great. Three answers, three opinions.

No shortage of that on this list!

[rennch]

Found the spiral bit:

http://www2.towerhobbies.com/cgi-bin/wti0001p?&P=WR&I=LXYA57

I feel like I might have a bit more control with this vs. a saw.

[Zeke]

Not so sure about the control. If you had a guide, yes. But spiral cutters tend to wander. A saw can be tracked. If you use any of the above, cut a smaller hole than you desire for 2 reasons: (1) to make sure you are centered where you like (test fit) and (2) so you can smooth to your line with a less aggressive method such as a drum sander attachment to your drill motor (variable speed preferred).

Paint the edges of your cut to prevent water from entering (not a big deal, but if there are any possibilities, water will find them).

[rennch]

I have a rotary fitting on my dremel that might let me get a perfect cut. I was going to attach a piece of string to a screw, and attach it to the dremel to create a "compass" of sorts. That's the plan anyway.

[Hoss3.0]

Try a few tests cuts with the Dremmel before. See if its easier to cut counter clockwise or clockwise. The rotation of the bit will make it wander more one way than the other. I just cant remember which way...sorry. If you can attach a "blank" (sheet metal cut to size) to it you could follow that arc. Go slow and start small. Good luck.

[Jeff Alton]

emptyo, yep, that is the one. Use two hands on the tool!

Cheers