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Permalink Reply by TN Twang on May 29, 2015 at 8:58am

After ruining several, I've come up with a technique that seems to work.

1. cover affected area with masking tape on both sides (easier to mark and the bit doesn't slip)

2. mark and dimple the center of the hole with a nail or punch

3. drill small hole (1/4" or less) The smaller the hole, the less tendency to tear out the flimsy metal

4. use conical "burr" bit to expand small hole to desired size--essentially filing away the metal all the way around

5. for multiple holes of same size, put tape around the cone bit partway up from the tip so you hit the tape just as the hole gets big enough

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Permalink Reply by The Phrygian Kid on May 29, 2015 at 11:09am

Make the hole in a scrap of sheet metal (perhaps part of a tin you screwed up previously) which is only barely larger than the hole, perhaps a quarter to half inch bigger all around.
Position this on the inside of the cookie tin lid right where you want the hole and temporarily tape it down.
Cut a hole through the lid in the center of the desired soundhole with a small grinding wheel in a dremel and work your way around the sound hole folding the lid in and around the template, which will be clamped inside and become part of the lid. You'll need to grind a few slots right up to the holes edge at corners and the like in order to comply with the shape you've made, but nearly all of the edge should be a rounded over fold rather than a sharp thin edge.

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Permalink Reply by Titch the Clown on May 29, 2015 at 12:17pm

I don't bother 

I use a no cut method leaving a sound hole beside the neck. This works best on square tins and not so good on round ones.

See how I do it in this instructable. 

http://m.instructables.com/id/Ford-mini-glovebox-guitarukulele/

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Permalink Reply by John Sawyer on May 29, 2015 at 2:02pm

The best way to make a hole is to use a Chassis punch, but they're not cheap.

A step drill does a great job on sheet metal... HF has a pair up to 1-5/8" 

http://www.harborfreight.com/2-piece-titanium-nitride-coated-high-s...

HF also has a knockout punch set that should work.  $25... several sizes up to 1-1/4

http://www.harborfreight.com/knockout-punch-kit-91201.html

bullet holes would look cool...

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Permalink Reply by TN Twang on May 31, 2015 at 9:44am

Haven't used a chassis punch since aluminum chassis caught on in the 1950s. Wondered where I could get one. The HF knockout punch looks like a similar arrangement. Gotta' give 'em a visit...

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Permalink Reply by Groucho on June 1, 2015 at 2:42am

I like your idea to use the melamine chopstick for the nut. 

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Permalink Reply by john mackay on May 29, 2015 at 10:31pm

you'll need support for cutting sound holes.

I put a piece of wood underneath where I'm about to drill or cut a hole.

never had a problem using this method.

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Permalink Reply by Will King on May 30, 2015 at 3:58am

I back the can with a wood block and pound a nail through.  Without any backing I use a step drill to drill it out to the size I want.  The drill rounds the sharp edges down into the can.  Most of the time I put the holes on the sides of the can so it won't mess up the nice picture on the top.

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Permalink Reply by The Capo Kid on May 31, 2015 at 9:16am

I bought a Step Drill Bit 6mm to 30mm and quite pleased the clean hole it cut ?  I'm going to glue the grommet's over the holes to finish it off ...  and thanks for all the reply's ...

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