Panel work - enlarging an existing hole

Does anyone know a nifty trick for enlarging an existing instrument hole from 2" to 2 1/4"? Will a Greenlee punch work? There isn't enough access to clamp a blank in place and then drill the larger sized hole. And the option of using a template and a Dremel tool is something I'd like to avoid.

Here's what I'd try:

Get a 2" and a 2 1/4" Milwaukee "Hole Dozer" hole saw that will fit the same pilot bit. With the 2", cut a plug out of a stack of plywood scrap that is taller than the inner depth of the 2 1/4".

Next, put the plug over the pilot bit, and run it all the way down into the 2 1/4 hole saw blade. Block your work piece up slightly so the plug penetrates the hole you're enlarging. You could cut a 2" hole another piece of scrap to use back up the work piece. The wood plug would go through the work piece and into the wood below it.

Take your time to line every thing up and clamp it down so it won't move. Maybe practice on some scrap aluminum before trying it on your work piece.

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It just dawned on me that you're probably doing this on an instrument panel that is already installed and not something you can clamp down on a drill press. I'd still give the 2" plug over the pilot bit a try. Have to be careful about FOD though.

I was thinking you take the 2-1/4" hole saw and drill a hole in a piece of 3/4" plywood or MDF. Then position that piece of plywood over the panel and clamp it down. If you can get to the original mounting screw holes you could screw the wood into position. Then use the hole saw with the plywood hole as a template so the hole saw can't move out of position as you are drilling the 2-1/4" hole in the panel.

You could also use a flush trim router bit and a router with the plywood as a template.

I did this once on an installed panel

A bit long winded .... but "safe"

1) I scribed a very accurate 2 1/4" dia reference line
2) Then used a power file (minature belt sander) to carefully "rough" the hole out
3) To refine and round the hole I used contact adhesive to fix some 120 grit wet & dry abrasive paper around the outside of a metal can of roughly 2" diameter (the nearer to finished diameter the better). I then sanded the remaining material (by rotating the tool rather than sawing with it) right up to my line

As I said, probably an hours work - but the result was pretty much perfect and I thought it was lower risk than trying to hole saw or punch the material out (the panel was pretty flimsy with all the other holes in it.)

I like the idea of cutting a 2" plug to use as a guide, will need to build the diameter back up however to make-up for the kerf of the saw blade.

Also, the < 2 1/4" abrasive can idea is a good one.

Any other ideas? Has anyone tried the Greenlee punch when there is so little remaining material to remove like what I'm faced with? I'm concerned it might really distort the panel. I don't have that size punch but can borrow one.

This will work ... you won't get it perfectly centered as with the normal method of using the tool, you'll have to eye ball it, but it will surely punch the hole clean without any collateral damage:

https://www.aircraftspruce.com/catalog/inpages/ats123chole.php?clickkey=13218

(duplicate your hole on scrap of the same thickness and run a few practice punches)

rmarshall234 said:

Has anyone tried the Greenlee punch when there is so little remaining material to remove like what I'm faced with? I'm concerned it might really distort the panel. I don't have that size punch but can borrow one.

Click to expand...

I think the Greenlee will cut without distortion because it has shallow shear angle. Why not punch a 2" hole in scrap aluminum and then try 2-1/4" Greenlee to enlarge?

mark the 2 1/4 hole and then use a 1 1/2 inch drum in a die grinder and run it around the hole with steady pressure and even speed and you will get it just about perfect. give it a few practice runs on scrap first. works great.

Thanks for all the tips, guys.

I just realized the combination punch that I have available as a loaner (same as in the link) won't work because of clearance issues.

I cut a template with mounting holes from heavy alum stock and will use that to enlarge the hole. The combination of a Dremel tool, deburring tool, drum sander and can, should get the job done.

It's amazing how much time one little obstacle like this can consume.

EAA has an excellent video on exactly this. Possibly by Brian Carpenter, anyway, google search or YouTube and you?ll find it.
Involves using a 2? plug/guide...

OK thanks, I'll check it out but after-the-fact. I cut the hole and installed the gauge today and it turned out great and was not too time-consuming.

Template, Dremel, deburring tool, and the abrasive can. Kudos to the guy that recommended the can wrapped in abrasives! It was "the bomb", and totally cleaned up the roughness and rounded out the hole perfectly.

This forum rocks.