New Design Proto Build - Lyra

preeb

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New model Lyra has been in the design pipe for 2 years now because I wanted to do a semi hollow that will make sense and bring something new to the table.
Somewhat hard to define, a semi hollow guitar can be many different things.. a Gibson ES-3x5, Thinline Telecaster, Semi hollow PRS and the list goes on and on but they all share one factor, they are not completely solid nor are they fully hollow (-; This may sound simple but there's a lot going on in that niche that may confuse anybody who's looking for a semi hollow sound. it is all over the place.
Some so called "semi hollow" designs sound just like a bad solid body lacking low end definition but look cool with that F hole (Yeah!!) and some are awesome like an old 335 but may be a little too large, some are simply solid body guitars with a little cavity under the F hole... etc...

For the sake of this build thread I will define a semi hollow guitar as being as close to a quality hollow body instrument but without that low end feedback and as close to a solid body as far as the focused and punchy tone. NOT in the middle between a hollow and a solid... as this may suggest compromising or giving up the qualities of both, but rather having the best of both worlds.
 

preeb

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The Lyra will retain the 13" width of my other models and therefore I will need to maximize the "hollowness" to achieve the goal.
The plan is to have a unique true floating arched top that can be tuned and will have vent holes (I would say F holes but they are not in an F shape) over a hollow shell that has a solid core between the neck and the bridge. Having that core intact and massive enough will retain the "solidness" while the floating top and the hollow chamber bellow it will add that full "hollowness".
I will be doing two proto builds (for now) to be able to compare between different wood types that I'm considering. For the initial two builds I will be using Mahogany backs on both with mahogany and maple tops.
 

preeb

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Body shells will be carved out of old Cuban Mahogany that I had drying since 2001. This wood is dense and very stable.
I will select two blanks from the same board with straight grain and medium weight.
The tops will be figured Cuban Mahogany and Old maple.

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Trued

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and sanded to final thickness

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Most of the build will be done on a CNC cutter. I usually prefer to cut manually on the pin router and I do it way faster than my CNC..
but this build will require some CNC work and you will see why soon..
I select the body shell location on the blank and drill the index/alignment pin holes for the jigs and CNC table

IMG_20190514_093002.jpg~original


like this

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Blanks are cut down to size

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Weight is also documented for future reference

IMG_20190514_093331.jpg~original
 

preeb

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I let the bodies sit for 24 hours to acclimate and verify they are still true and ready for the next step.
When shelling a one piece blank it is important to select the proper stable/dry wood and to inspect after every machining stage. It needs to stay straight and true without warping.

IMG_20190514_093405.jpg~original




Top plate blanks are trued

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and edged

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tested for zero gap glue line

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and glued. The mahogany is glued with brown Urea Formaldehyde

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and the maple with creme UF

IMG_20190514_104249.jpg~original
 

preeb

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The Mahogany body shell is designed to have a slightly thicker back than spec to allow for tuning and matching with the top.
This is the CNC program for the shell showing the left alone center core. Note that the hollow void is very large and runs around the core.
The volume of the void is about the same as an old ES-335 void.

IMG_20190514_094213.jpg~original




Those are the CNC table pins that correspond with the previously drilled index holes on the body blanks

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Program loaded

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and run

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like this..
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For the proto I run this program in a few stages and remove the blank for tapping. I need to get to A note so I keep cutting until I get there...

IMG_20190514_104352.jpg~original




Done.. and now you understand why it is called "LYRA" (-;

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Next cut is the wiring channel

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and the dreaded CNC tooling marks clean up..

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Once again, 24 hours rest and testing for warpage

IMG_20190514_113540.jpg~original
 
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preeb

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Once top plate blanks are cured it's time to work them a little.
Since the top is going to be a true arched top I will need to carve it to correct thickness and tune it, but I will be doing this in two stages.
First I will carve the inner side, join the top to the shell and only when the body is complete I will tune it along with tuning the shell back.

Here's the CNC program for the inner side of the top plate

Roughing
IMG_20190514_143242.jpg~original


and finishing
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the cut

IMG_20190515_105956.jpg~original


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The inner side of a carved tops needs to be smooth and sealed.
Here I sand it to remove any machining marks

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like that

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and seal it with sprayed Shellac

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I now pencil the body outline

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and remove the Shellac on the gluing joint surface by sanding it off.
UF glue doesn't work properly over Shellac...

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Indexing pins are inserted and cut. This will ensure correct placement of the top over the shell when gluing

IMG_20190515_111257.jpg~original


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and the tops are placed on top of the shells to verity 100% fitment with no warpage before gluing

IMG_20190515_111447.jpg~original


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Brown UF

IMG_20190516_090337.jpg~original



and the top is glued and pressed under 20 tons of pressure with the rest of the batch.
This will ensure the glue is pressed so hard that the wood parts will touch and create the best possible tone transfer when dry.

IMG_20190516_092245.jpg~original
 

preeb

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As the glue cures I will start working on the necks and boards.
Necks will be the same as the Bone necks with the same truss-rod system which has proven itself over the last few years to be superior to the older 50's Gibson design.
The headstock area is far stronger and the tone transfer is better.
The headstock of the Lyra will be completely different from the Bone of course being a whole new design.

Since I'm trying to A/B the Mahogavy VS the Maple top I need to make sure everything else is identical to isolate the comparison to the tops only.


I cut the two necks out of the same billet

IMG_20190514_114355.jpg~original


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Slice them to thickness

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and make sure the fillet it completely straight. If not the necks will be discarded

IMG_20190514_115913.jpg~original




fingerboard face is trued only after the necks are roughly cut and any inner stresses are removed

IMG_20190514_115346.jpg~original




Necks will need to acclimate and rest over the weekend and checked for any movement.
 

preeb

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I will be using dense Brazilian Rosewood fingerboards for the Lyra.
Once again, I sliced and thicknessed a few boards and selected those with identical tap note to get the "same" neck on both protos

IMG_20190516_101652.jpg~original



Trimmed

IMG_20190516_104150.jpg~original




and set aside to slowly acclimate, pressed against each other as I don't want them to acclimate too fast and possibly warp.

I roughed the neck outlines on the pin router and cut the tenons on the saw but forgot to take photos... anyway.. here's the crop resting until Monday

IMG_20190516_111800.jpg~original
 
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tigger

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For the proto I run this program in a few stages and remove the blank for tapping. I need to get to A note so I keep cutting until I get there

So you want the body frequency of resonation to be A? Can you be sure it will be since the top is not on and there is a lot of wood around? Or is it really just the thin back that resonates and therefore the borders are just anchors?
 

preeb

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So you want the body frequency of resonation to be A? Can you be sure it will be since the top is not on and there is a lot of wood around? Or is it really just the thin back that resonates and therefore the borders are just anchors?

Yes, it is the thinner area of the back vibrating against the thicker frame and solid center. The A is just a good starting point at this early stage and it will completely change later on when we get to that point in the build. Basically, the idea is to have the guitar assembled with the neck glued in before tuning the back. The top is then tuned to match the back by working the thickness and recurve. Naturally, the two guitars will have different tuning because of the different top densities (maple vs mahogany).
 
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