Louis Electric

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more... Builder ProfileGearDecember 2007John Dick

Sandwiched Tops

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The Nomex honeycomb needs to be cut to shape before gluing. Place the redwood core on the outside skin of the top (the top must be rosette side down), and tape it down with masking tape. Lay a rectangle of Nomex next to the core as close as possible and tape that to the center seam. With very sharp scissors, gently trim the Nomex to the shape of the top, using the top’s edges as a guide. Repeat this process for the other side. Try to keep the Nomex as still and stable as possible as you cut to keep the edges as clean and close as possible. Remove the masking tape and wipe any dust or fuzz off the top when you’re done.

On a piece of scrap wood or polyethylene, spread a small amount of Gorilla Glue, approximately three grams. Roll the glue evenly out on the scrap with a 1.5” rubber roller so it is spread evenly on the roller. Apply a thin film to the redwood core, just enough so the wood looks barely wet. Place the redwood core onto the top skin (with the rosette still facing down away from the gluing surface), and press it into place, carefully aligning with your marks. Spread more glue on the disposable piece so that it covers an area large enough to lay the honeycomb on it – approximately 21 grams, which will be thick enough to deposit a sufficient amount of glue on the edges of the Nomex. You won’t be applying glue to the top this time, but simply laying the Nomex in the glue on the scrap without mashing down any of the cells and putting it into position on the prepared top. Place the honeycomb so it butts against the redwood core, but do not press it down – you want the cell walls of the Nomex to be completely upright so they can bond with both sides of the sandwich. Using masking tape, secure the edge of the Nomex to the redwood core, making sure there are no gaps. Run a piece of tape down the entire seam, as it can shift in the vacuum press and create a gap. Repeat for the opposite side.

Place in a vacuum press, covering the wet surface with a black plastic trash bag (Gorilla Glue won’t stick to the bag) and allow it to set up. As the Gorilla Glue dries, it will expand to three or four times its original volume within the first 30 minutes. A small fillet should form between the glue and the honeycomb walls; if the fillet foams you have used too much glue (Gorilla Glue in a thin film shouldn’t foam). The top should stay in the press for approximately 90 minutes. Check the glue that was on your scrap piece for dryness. When it is dry, take the top out of the press. Once dry, any glue that has migrated to the top of the cell walls shouldn’t stick to the tape. If you can’t remove the tape, it isn’t dry enough.

The edge of the Nomex needs to be “tied” to the redwood using a very long-acting epoxy. John prefers epoxy for laminating carbon fiber and fiberglass (Silvertip Laminating Resin from systemthree.com). Use a veterinary syringe with a number 16 or 18 gauge needle with the sharp tip ground off. Mix the epoxy according to the package directions. Remove the plunger from the syringe and pour the liquid into the tube, being sure to tip the plunger back in and allow the liquid to drain backward so you can remove the air from the tube when you replace it without losing all the epoxy. Put the needle into the end, and use the syringe to fill the gap only between the edge of the honeycomb and the redwood core. Allow to dry overnight.

Sandwiched Tops The next day, run the half completed top through your drum sander to plane and level the core to your desired thickness. The total thickness of the finished top should be the same as you prefer for a solid top.

Once the desired thickness is reached, carefully go over the Nomex side with an orbital sander to make sure there is no fuzz left by the thickness sanding belt. Be sure to blow or vacuum all dust out of the honeycomb.

Take your inside skin, and apply as you did with the inner core, spreading a thin film of glue on the inside surface using your roller. Again, use only enough glue so that the surface just appears to be wet – approximately six grams of glue. Glue can be drawn from areas that appear to be wetter to dryer areas using the roller. You can use pieces of blue masking tape to secure the skin and the core together. After another 90 minutes in the vacuum press, you have a finished top. Don’t try to flex it just yet, but it can be tapped for tone. Allow another hour for it to dry before flexing. It will continue to stiffen for another 24 hours.


Finishing Up
Since the Nomex adds so much strength to the top, it can be braced significantly lighter for far freer vibration. The sandwich top is joined to the body just like any other guitar, and the binding and perfling can be applied just like on a solid top. John does a satin French polish to keep the finish as light as possible, in keeping with the ultra-light bracing.

Sandwiched Tops It seems like a lot of extra work and trouble; however, the added strength, stability, volume and sustain that these tops give a guitar is more than worth the effort. The beauty of the finished product is uncompromised and the tone is dramatically improved. The steel string makers who are adopting the sandwich top have had even more dramatic results. I played a dreadnaught made by guitar maker Curtis Paul for several days after it was made and was stunned by the clarity of the harmonics through the spectrum and by the additional tones it brought out. It usually takes a top several months to achieve maturity like that, but for this guitar it was literally hours – I am told that now after several years it is even richer. To my ear, the sound shimmered and soared like no guitar I’d ever heard, and it seemed remarkably stable through Iowa’s wild weather changes, too – always a plus for touring musicians.

John left one of his guitars at my house for me to work with and get a feel for as I wrote this article. Since I am used to a typical steel string neck, he brought along a custom model with a narrower and more familiar feeling neck. Having it around has been a remarkable experience, and has made me even more fascinated by John Dick’s innovations. I constantly find myself playing complex chords just to listen to them ring; they sustain almost as long as with my finest steel string and are every bit as loud. This guitar responds to the player’s input much more intimately than most steel string guitars, especially to subtle vibrato. It’s a powerful and beautiful addition to the rich palette of guitar traditions.



Hear the sandwich top guitar in action!

"Blues for Felix" by Charlie Byrd performed by John Dowdall on a 2001 John Dick double top, cedar top guitar.

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An original song from songwriter Rick McCarty played on a John Dick sandwich top.

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Pat Smith, a guitarist/arranger hailing from Evanston, Illinois, plays a jazzy track with the sandwich top guitar.

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