Replies to This Discussion

Permalink Reply by ChickenboneJohn on June 6, 2011 at 9:59pm

I use hole saws (the type used by plumbers & electricians for doing cutouts for pipes and light fittings) and a drill press...but make sure you get a decent set, the rigid pressed steel cup type, not the cheap flimsy 'spring steel' pattern. I've got a couple of sets, diameters from 32mm to 86mm

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Permalink Reply by Seaman Jay on June 6, 2011 at 11:04pm

Hole saw for big round sound holes[1]. Wood bits for smaller. Jigsaw for all the rest. 

 

And - don't forget to put a piece of wood under the soundboard before drilling. It may split otherwise.

 

[1]I was too lazy to bring my bits from the attic and started with the dremel. That's the only "semi-round" sound hole I have on my CBG... See my pics gallery ;-)

 

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Permalink Reply by Outhouse Instruments on June 6, 2011 at 11:45pm

I use the paddle or spade bits. A 3/4 inch hole fits the trim I use. ( a "pocket door" pull with the bottom cut out).

 

 

AFKAM

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Permalink Reply by Roadkill a.k.a. John Maw on June 7, 2011 at 4:13am

I use milling cutters (normally four or six flute) or slot drills (two flute). They should be super sharp. Keep them turning fast and just rest them on the surface for a moment with very light pressure and let them work their way through the surface. Once they have got past the first half millimetre (which is the dangerous bit) then you can take them in faster. If you need the holes to be good on both sides make sure there is some sacraficial wood behind the piece you are cutting so that it doesn't splinter as it breaks though.

It helps to clamp the work down if you can do that without marking it. If you have fine feed on the drill press, as you have with a milling machine, that will help.

This will give you holes that don't need trims and look smooth. If you are using a wooden box which has a finish on it the edge of the holes will look lighter. Put a little linseed oil (or danish, tung or tru oil) on just to darken it to match the finish of the box.

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Permalink Reply by Diane in Chicago on June 7, 2011 at 4:24am

I use forstner bits for circles.  Clean and perfect, even on plywood.  I had troubles with tearout when I used paddle bits - even the ones with the corner teeth.

 

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Permalink Reply by Mungo Park on June 7, 2011 at 2:13pm

Diane has the same idea as I do:

I use forstner bits for circles.  Clean and perfect, even on plywood.  I had troubles with tearout when I used paddle bits - even the ones with the corner teeth.

 

I thought you were referring to the ideal size for the best acoustics, I think about the size of a egg is about right.

                                       Cheers Ron

 

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Permalink Reply by Diane in Chicago on June 7, 2011 at 3:12pm

Actually, there was a blistering debate years back on the old Yahoo site about the perfect size for a soundhole.  After studying up on the work of physicist Hermann von Helmholtz, the verdict was that for an average cigar box, the optimal size was about that of a quarter.  Otherwise you are taking away too much surface which is needed for vibration in order to get the best volume.

 

However, I don't know if any definitive studies were done.  ;->

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Permalink Reply by David Tutterrow GutBucketGuitars on June 7, 2011 at 4:49pm

This

Diane in Chicago said:

I use forstner bits for circles.  Clean and perfect, even on plywood.  I had troubles with tearout when I used paddle bits - even the ones with the corner teeth.

 

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Permalink Reply by Rand Moore on June 7, 2011 at 4:58pm

Thanks for that tip, Diane. I guess my sound holes tend to be too small. I will have to try enlarging them and see if that improves sound volume. Too bad I don't have a U.S. quarter handy...  A Google search says a U.S. quarter is 31/32nds of an inch in diameter, which is 24.6 mm. Guess that will be close enough.

-Rand.

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Permalink Reply by Alex on June 7, 2011 at 6:36pm

If you have an electric drill then you may want to use a hole saw if your goıng for a larger sound hole

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Permalink Reply by David L. on June 8, 2011 at 12:52am

I only have a small electric hand drill and no drill press- would forstner bits work with this?  I read somewhere that they are guided by the outer rim of the bit as opposed to a central point of the bit which makes me think without the drill press it would be hard to get the hole centred and to stop the bit wandering off as the hole is started.  Is there a kind of hybrid - forstner plus a drill spike in the centre of the bit for drilling without a drill press?

 

In the past I have used curtain grommets to make the holes look neater and for my last build and my current one I have gone for f holes slotted with a set of small hand files using f hole templates previously posted by Diane.

David

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Permalink Reply by Diane in Chicago on June 8, 2011 at 2:46am

On my forstner bits, there is a center spike to get you on spot - I usually use an awl to make a divot in the wood for my desired center.  The next part of the drill bit that touches the wood is the outer cutting ring, and once that is started into the wood -- that drill isn't going to wander anywhere!  Just be sure your drill is as perpendicular as you can get it and go slow and easy.  Since it is  a ring and not a paddle, there is no jumping about.  Much easier to control - and almost no tearout on the back.

 

Nice F hole!

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