Best way to make larger instrument holes in existing panel?

I am in the process of saying goodbye to my old Isspro fuel quantity, and oil temp/pressure gages. I am going to replace them with electronics intnl. guages.
The existing holes are 2", and the new guages require 2 1/4" holes.

What is the best way to open these holes up?

An instrument hole punch would be best I think but how do you keep it centered with a 2" "pilot hole"?

No doubt there is a tool for this but I don't happen to know what it is.

+1 for the punch

I used a punch for this exact operation. Mark the new circle on the panel and get the punch started manually until makes contact with the panel and holds itself in place. I was very worried about keeping it centered but it turned out to be quite simple.

I've also done this operation with nibblers and a file... and that made an unholy mess of aluminum dust. I recommend the punch.

-jon

thanks much, I didn't know if it would grip and stay in position.

one method.....

I'm no machinist, but if you drill the 4 new instrument screw holes, then use these to attach a sacrificial square of aluminum behind the panel, this will be your pilot hole guide piece.
you can then use the punch, or a more primitive hole saw to cut thru the panel, and slightly into your scrap piece.
File, dremel, finish as needed.
Your local avionics shop may loan you a punch for the standard rental fee ( a case of Big Rock suds, or bottle of rye.

Rye

Rye - Also known as Crown Royal down south

Punch

Once that punch starts to bite it is not going anywhere. Go slow.

thanks for all the input. I did find a hole punch for a good price and have it on order.