Santos Hernandez Plan and Neck Angle Set-up (Full Version)

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diazf -> Santos Hernandez Plan and Neck Angle Set-up (Sep. 15 2009 12:08:29)

Hi all--
I've been working on building the Roy Courtnall's Santos Hernandez 1933 Blanca plan and have a few questions that are not readily apparent in the book or plan drawings that I hope some members can answer/clarify.

The first questions is if the blanca had a curved soundboard. From other Blanca's I've seen there sometime is a very shallow curvature on the cross brace below the sound hole. There isn't any clear cross section indicating this.

The other question I have, is what is the neck angle on this guitar. From other readings and research, other luthiers have indicated that the neck angle to soundboard is not completely flat (180 degrees) but instead a few degrees / mm less tan completely flat as in the solera in Courtnall's book. The intent being to have a lower string height over the sound board as well as lower bridge height for playing flamenco. Anders broadly talks about this in his video 'El Guitarrero' but detailed measurements would be great.

Any information you can provide would be greatly helpful.
Thx.
FD



r0bbie -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 15 2009 13:50:33)

Hi Diazf,

I am not a Luther but I am building a guitar from the same plan and the same book. The neck described by Courtnall has a angle which is a little less than 180 degrees. On page 165 (if we have the same print) where the solera described you can see on drawing 11-4 that the "neck extension is ramped down by 3mm"

As I understand, this is less for a flamenco guitar. I posted the same question about the neck angle so maybe you can search for the replays I got. I don’t think you will get an exact figure because it seems somewhat unpredictable how the final angle turns out once the guitar is glued.
Anyway, I then decided that I would use 2mm instead of 3.

I dont understand the question about the curvature, but this could be because I'd rather speak Dutch :-)

I know William Cumpiano has written a book about guitar building where the curvature of the top is made by arching the cross brace below the soundhole and keep the area of the fan braces and bridge flat. (this makes life easyer I think) Courtnall uses the hollow solera to press the soundboard into a dome with the fan braces.

Hope this helps a bit and if not, just wait for the experts..

Rob.



jshelton5040 -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 15 2009 14:47:53)

quote:



The first questions is if the blanca had a curved soundboard. From other Blanca's I've seen there sometime is a very shallow curvature on the cross brace below the sound hole. There isn't any clear cross section indicating this.

The other question I have, is what is the neck angle on this guitar. From other readings and research, other luthiers have indicated that the neck angle to soundboard is not completely flat (180 degrees) but instead a few degrees / mm less tan completely flat as in the solera in Courtnall's book. The intent being to have a lower string height over the sound board as well as lower bridge height for playing flamenco. Anders broadly talks about this in his video 'El Guitarrero' but detailed measurements would be great.

Braces that run parallel with the grain of the top wood are forced into the shape of the solera until the glue sets up. Braces that run perpendicular to the grain of the top should be shaped by hand to fit the curvature of the solera.

I personally think 3mm is too much neck deflection but it depends on how much arch you build into the top. We use around 2 mm or slightly less. This can be done with an absolutely flat jig that holds the guitar body in place while the neck is swung downward. The measurement at the twelth fret should be around 2mm higher than the measurement at the nut. If the deflection is a little off you can compensate by tapering the fingerboard from end to end. It's difficult to describe this process in a few words.



tirofori -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 15 2009 16:30:54)

Hello diazf,
As to your second question: before you can decide about a neck angle you must decide what distance you want between the soundboard and the strings at the position you play the guitar, which is near the bridge. I think 8 mm is a good distance for a comfortable golpe but this is a matter of personal preference. In my experience the best thing to do is to draw the guitar sideways full-size as precisely as you can, including fretboard, bridge and string. I cannot answer your first question but when you have a good drawing you will clearly see the effect of a curved soundboard. Then you will be able to decide what neck angle you need, if any.
By the way, John Shelton says in his reaction that braces that run perpendicular to the grain should be shaped to fit the solera. I would be interested to know if that includes, in his opinion, the two closing braces.



diazf -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 15 2009 17:39:27)

Thanks to all of you.
Your advice has been very helpful and has help me confirm a few items. Based on your collective comments, I drew an overlay over the full scale side section of the Santos drawings and approximated the following dimensions, which probably vary by guitar but give me good starting point. Dimensions are approximate.

Bridge Saddle Height: 7 mm
Soundboard Height at bottom of sound hole: 8 mm
String Height at 12th fret: 3 mm
String Height at Nut: 3 mm
Neck Angle: 2 to 2.5mm tilting up so Nut is higher than the bridge
The perpendicular brace is shaped (carved radius) to about 2mm dome on the top.

Based on this, the bridge height and thickness seems too big. Is it possible to get away with a 2- 3 mm thick bridge plate thickness versus the 4 mm specified for the base part?

I also take it that I'll have to sand the bottom of the fingerboard that meets the top of the soundboard to accommodate the neck angle.

Also the Santos indicates no bridge plate is needed under the soundboard. I've read that Torres and Romanillos considered this bridge plate unnecessary as it actually created stress to the soundboard. Modern luthiers Eric Monrad and Glen Canin have been using small latices instead of wood plate to supplement the bridge, any thoughts?

Any thoughts on running solid laminated lining instead of traditional kerfing for stiffer body? And continuing above the end block for better sound transmission and reduced stress on the soundboard?

John, I'll definitely use your recommendation on the Solera to get the neck angle. Saves me a lot of sanding.

Sorry for the mouthful but this exciting stuff.
Thanks again.
--Fabian



Stephen Eden -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 15 2009 23:02:58)

I use about 1.5mm - 2mm for the neck angle.

For doming on the front i use a dish with a 25' radius and for the back a dish with a 15' radius. The lower harmonic bar is shaped in the dish the upper harmonic bar is flat to accomadate for the fingerboard. the fan bracing is light enough to be pressed into shape while gluing. when the glue the set the bars will hold the shape of the dome.

For me the string height at the bridge is 9 mm bass side and 8.5 on the treble.
The string hieght at the 12th is 3 on the bass an 1.5 on the treble.

A good way to achieve a good action and string height from the sound board is afteryou put the fingerboard on, plane it so where the bridge will be. If the finger board were to extend all of the way down it would be 4mm high on the treble side and 3mm on the bass side I hope this helps

the bridge is 6.8mm thick.

I'd say then plans in courtnells book are fairly limited in what they actually give you though. For me I would use the bracing pattern and then thickness them down as you see fit these can be guide lines.



jshelton5040 -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 16 2009 6:50:08)

quote:

ORIGINAL:
By the way, John Shelton says in his reaction that braces that run perpendicular to the grain should be shaped to fit the solera. I would be interested to know if that includes, in his opinion, the two closing braces.

No, I was only referring to the tone bars. Of course some people use a fairly tall brace under the bridge. If I were to do that I would shape it rather than press it in.



jshelton5040 -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 16 2009 7:05:13)

quote:

ORIGINAL: SEden
The lower harmonic bar is shaped in the dish the upper harmonic bar is flat to accomadate for the fingerboard.


Stephen,
When I carve a solera the center line of the arch (actually an ellipse since the apex is under the saddle) runs from the end block all the way to the 12th fret; therefore the upper cross brace is also very slightly arched. It makes fitting the fingerboard much more challenging but I think it has a beneficial effect on the guitar's voice. Years ago I was examining a Fleta and it appeared that it was built this way, that's where the idea came from.

John



r0bbie -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 16 2009 8:30:30)

John,

Can you explain what the effect is on the voice of the guitar when its dome runs from tail to the 12d fret? And if I may ask, does the dome starts at the side's or is there a little flat edge on the solera where the sides are gued on?

I wonder because when I glued the side's on the the flat edge of the solera, the dome got less then when the side's where not gleud on.

Rob.



jshelton5040 -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 16 2009 14:47:08)

quote:

ORIGINAL:
Can you explain what the effect is on the voice of the guitar when its dome runs from tail to the 12d fret? And if I may ask, does the dome starts at the side's or is there a little flat edge on the solera where the sides are gued on?

I wonder because when I glued the side's on the the flat edge of the solera, the dome got less then when the side's where not gleud on.

As always in guitar making it's nothing but conjecture. I have the impression that shaping the dome in this way adds percussion or makes the guitar more responsive. I usually think of it as making the guitar faster. Nebulous terms at best but how else do you describe an effect especially when you're just guessing anyway?

I don't glue the back on using the solera. I made another jig that supports the guitar along the sides and allows me to swing the neck any amount I want. It does take some of the dome out when you glue the back on but you simply compensate by increasing the height of the arch when carving the solera. By the way, it helps if you taper the edges of the sides a little to compensate for the arch and of course you have to put a slight angle on the top of the tentallones as well. I made several soleras before ending up with one that I was satisfied with. It's the only one we've used for years now.



diazf -> RE: Santos Hernandez Plan and Neck Angle Set-up (Sep. 16 2009 17:42:28)

Thanks for the advice. I will keep it in mind when setting up the fingerboard. A neck angle of 1.5 to 2 mm seems to be the consensus for a Flamenco guitar. Roy Courtnall replied to my questions and had this to say...

You should always have a curvature on the soundboard, for any type of guitar. This always makes it stronger and sound better.

The neck is usually not quite flat. The important thing is to make the taper of the fingerboard and the height of the bridge in such a way as to give the string height you want.

For a flamenco, 1 or 2 mm raised at the nut is enough because you do not want a high string action

Thanks.



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