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Cornerstone Double Top Construction
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Author:  peterm [ Fri Nov 10, 2006 2:32 pm ]
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Well, the process was posted on another forum, so I guess I'd share it with the rest of the family!

1. First I got the bottom top (bottom top??) Englemann Spruce cut and I marked exactly where the braces where going to be glued on.

.
2. the goal was to hollow out most of the lower bout area to reduce weight without sacrificing strength.
3. Instead of using Nomex to reinforce the hollow areas, I decided to route out holes in a honeycomb style removing some material while keeping the top strong. That allowed for less glue usage while utilizing most of the original top.


4. Top was then sanded to thickness and glued onto the redwood top.

The total top thickness is now at about .125" to .115" but the lower bout area, the area that's responsible for most of the top movement, is now about 40% lighter.

I left the center seam untouched, and the brace areas also to ensure and maximize strength.

As of right now tap tone is amazing and I guess we'll know more after the guitar is strung up.

And here is the almost finished guitar!



Thanks for watching! peterm39031.9486458333
Author:  CarltonM [ Fri Nov 10, 2006 3:14 pm ]
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An interesting concept, Peter, and no matter how it sounds, it's looking really good! Thanks for the update.
Author:  Jim Watts [ Fri Nov 10, 2006 3:20 pm ]
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Peter,
Did you leave the holes exposed on the inside? Very interesting.
Author:  peterm [ Fri Nov 10, 2006 3:23 pm ]
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[QUOTE=Jim_W] Peter,
Did you leave the holes exposed on the inside? Very interesting.[/QUOTE]

Nope, if you notice closely the brace positioning is backwards to fit precisely in the correct place when flipping and glueing to the top.

Here it is:


peterm39031.9756365741
Author:  old man [ Fri Nov 10, 2006 3:28 pm ]
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I don't understand "double top" theory. Isn't adding to the mass of the top going to make it less responsive? Looks like you'd need some heeaavvyy strings to drive that thing. Enlighten me, please.

Ron
Author:  Jim Watts [ Fri Nov 10, 2006 3:39 pm ]
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Got it. That makes much more sense to me.
Cool.
Ron, the modern double top is typically constructed from a thin spruce skin, some nomex honeycomb, and another spruce skin. The spruce skins are typically in the nieghborhood of .03 think. This structure results in a lighter top, more stable top. It also flexes a little different.
Peter's top shown here is different from most double tops.
Author:  peterm [ Fri Nov 10, 2006 3:42 pm ]
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[QUOTE=old man] I don't understand "double top" theory. Isn't adding to the mass of the top going to make it less responsive? Looks like you'd need some heeaavvyy strings to drive that thing. Enlighten me, please.

Ron[/QUOTE]
Ron, exactly what Jim said. My top is not heavier than a regular top....in fact its lighter. Both tops combined are approx .120 thick but weigh less since mass has been removed. peterm39031.9885185185
Author:  old man [ Fri Nov 10, 2006 3:47 pm ]
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Thanks, guys. Hope you can post a sound file when you finish, Peter.

Ron
Author:  Serge Poirier [ Fri Nov 10, 2006 5:05 pm ]
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Thanks for the update Peter, looking great and really good info here, i might give that a shot in the future!
Author:  peterm [ Sat Nov 11, 2006 5:53 am ]
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[QUOTE=old man] Thanks, guys. Hope you can post a sound file when you finish, Peter.

Ron[/QUOTE]

I sure will! Can't wait to hear it!
Author:  Joe Beaver [ Sat Nov 11, 2006 6:26 am ]
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Peter,

Very inventive!!!

Do I have this right?
Top layer - Redwood
Middle layer- routed out spruce? (replaces nomex)
Bottom layer - spruce?

Brace it light?

The whole thing is around .120"?

It sounds to me like you may be onto something here....Good work
Author:  Sam Price [ Sat Nov 11, 2006 6:55 am ]
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I'm glad you followed this theory through.
Author:  Michael McBroom [ Sat Nov 11, 2006 6:58 am ]
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Peter,

What sort of glue did you use to glue the tops together? Any special procedure to insure no voids?

Best,

Michael
Author:  peterm [ Sat Nov 11, 2006 7:20 am ]
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[QUOTE=Michael McBroom] Peter,

What sort of glue did you use to glue the tops together? Any special procedure to insure no voids?

Best,

Michael
[/QUOTE]

Michael, I used good ol' LMI white! and clamped it under about 500lbs of cement blocks!
Author:  BruceH [ Sat Nov 11, 2006 9:12 am ]
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[QUOTE=Hesh1956] The possibility of running the grain 90 degrees off on the middle layer?

What do you think?[/QUOTE]

I think you've invented plywood, Hesh.
Author:  peterm [ Sat Nov 11, 2006 9:17 am ]
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[QUOTE=Hesh1956] Peter very, very cool and this is a great thread as well.

Have you considered the following.

Making a three layer top with the middle layer having the holes and many more of them. They would not need to avoid the brace locations since the other layers would be in contact with the braces.

Each layer could be much thinner and perhaps shoot for an overall thickness of .090 or less.

The possibility of running the grain 90 degrees off on the middle layer?

What do you think?[/QUOTE]

making 3 layers is a possible way to do it but you'd need another layer of glue...

If you ran one of the tops orienting the grain at 90 degrees you'd get a very stiff top with no lateral movement killing most of the top movement.... not the idea here!
Author:  Lillian F-W [ Sat Nov 11, 2006 9:26 am ]
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[QUOTE=peterm] [QUOTE=Jim_W] Peter,
Did you leave the holes exposed on the inside? Very interesting.[/QUOTE]

Nope, if you notice closely the brace positioning is backwards to fit precisely in the correct place when flipping and glueing to the top.

Here it is:


[/QUOTE]

Okay, now I am confused. If you don't leave the holes exposed on the inside, do you cover them with another layer of spruce?
Author:  peterm [ Sat Nov 11, 2006 9:33 am ]
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[QUOTE=Aoibeann] [QUOTE=peterm] [QUOTE=Jim_W] Peter,
Did you leave the holes exposed on the inside? Very interesting.[/QUOTE]

Nope, if you notice closely the brace positioning is backwards to fit precisely in the correct place when flipping and glueing to the top.



Okay, now I am confused. If you don't leave the holes exposed on the inside, do you cover them with another layer of spruce? [/QUOTE]

No, the holes are covered by the top wood... in the case the Sinker Redwood. They are now in between the 2 tops....making those areas now hollow!peterm39032.7320023148
Author:  Lillian F-W [ Sat Nov 11, 2006 9:42 am ]
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I understand the top, it was the inside I wasn't getting.
So, there are three layers? The redwood on the outside, the holey spruce and the spruce on the inside?
Author:  peterm [ Sat Nov 11, 2006 9:47 am ]
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no Lillian, 2 layers... the top layer and the spruce which is partially hollowed.

Author:  Alain Desforges [ Sat Nov 11, 2006 9:48 am ]
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Ohhhh!!!! Now I get it... the holes don't go all the way through the spruce... So the holes are facing the redwood... Hence the 'double top' designation... I was wondering why it wasn't called a 'triple top'?!

'I see' says the blind man, as he falls down the stairs...
Author:  Lillian F-W [ Sat Nov 11, 2006 9:50 am ]
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Ahhh, now it makes sense.
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