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If you draw it all out first - then you have a pretty good idea. Likewise following dimensions on a plan should also get you there. Boganovich has a pretty good method with a dummy fret board and a ruler to see how the strings will lay.

My process is to build as flat as possible and then check to see that a ruler going down the unfretted fret board lands right where the bottom of the saddle will be.

Maybe I am misunderstanding your question

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It's this new idea from recent decades that everyone gets a participation award. - MUX

on what instance are you at Filippo? you are using bolt on neck, right?
only made 2, but so far i put no angle to the neck related to the top, with a top dome of about 3mm, a bridge 8mm high and a fretboard 7mm thick with no taper.
this gave me an "almost ok" string action. i say almost because the saddle ended up a bit too low for my taste. for future corrections ill be compromised.
on flamencos i know they make a concave angle between the neck and top in order for the strings to land closer to the top and the bridge is lower. 6mm i´ve read.
in this case you need to tapper the glueing side of the fingerboad from the 12fret to the soundhole in order for it to adapt to that break angle.
i think i need to make a slight convex angle instead so i can have a taller saddle, but i havent figured out how to adapt the under glueing side of the fingerboard.

maybe you can get an idea from this link. He uses a dummy bridge and nut with a steel ruler to measure the action and to thickness the fingerboard.
its in spanish, but you know a picture is as good as...
http://www.rafaellopezehijo.com/diapason.htm

You really only need to know the position of the Neck at the Nut end - once you have established where that should be it will be consistent from one Guitar to the next, providing everything else is pretty much a constant. My model requires a forward 'lift' at the Nut of 2mm's, therefore I glue a little wooden tab 2 mm's below the surface at the side of the Neck. That allows me to lay a straightedge along the soundboard and aimed at the 'tab'. Of course the straightedge has to be adapted to take into account any doming, so my straightedge only registers at the base of the lower bout and at the edge of the top bout. In other words it is scooped out over the body section.
Failing that just calculate the thickness of the fretboard, height of the frets and then the action required. Make a dummy Nut, the same height of the strings sat in their grooves and a dummy Bridge/Saddle. Make a long wooden wedge shaped 'feeler gauge' for the 12th fret position. I place a mark on this wedge, so eg. I aim for 6.5mm f.board + 1 mm fret height + 3.5 mm string height = 11 mm above the Neck surface at the 12th fret position.

I want to know how Bruno (munen) is doing it!

As far as I can make out, for a standard set-up (3.5mm action) the string height above the soundboard at the saddle for one of Bruno's guitars should be 18mm, or 15mm if the soundboard has a cylindrical curve (fretboard thickness + fret height + 2*12th fret action) = height above soundboard at saddle (ignoring any relief). Hence 7+1+(2*3.5)=15mm. And then there's the issue of the curvature...

So Bruno, what's your secret?

BTW, the Rafael López site shows a taper on the fretboard, which is a fairly conventional way of doing things.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

That's right - the post above reminds me - typically a classical fret board is tapered, and in the process checked and tapered to meet the specific string height. Are you trying to build without tapering the fret board ?

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It's this new idea from recent decades that everyone gets a participation award. - MUX

I use a combination of four things to get the right action height.

-A neck "lift" of about 1.5 mm
-Top domed to around a 25' radius in the bridge area
-Tapered fretboard (around 6.5 mm at the nut to 4.5 mm at the SH)
-Bridge height (around 8-9mm plus saddle of around 2mm)

The first two are predetermined but the second two can be tailored for specific requirements.

Like David said, first lock in the relation of neck lift and dome. The rest, fingerboard and bridge/saddle, are left for fine tuning at the set up stage, but should be considered in the drawing/planning stage.

I find that dome (in millimeters) plus forward neck angle (in millimeters) usually add up to 5mm and this gets me in the right neighbourhood. For example, a 5mm dome has no forward neck angle, while a 3mm dome would have 2mm neck angle.

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Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/

no secrets.
havent measured but, height of strings above soundboard is around 10 or 11 mm.
string action is little higher for the 6th string, around 4mm. and i worked a relief on the fretboar of about 0.5mm

ill take a photo on these days.

I do not use a neck lift!
No need to when using a domed top-25-30
You'll have to plane(taper) the f.b. less because of this.
A 12 or 18 hole bridge helps with string angle over the saddle.
Draw out all details in full size.

My guitars are sweet & loud with great note to note separation.
I use radial bracing for classicals & a Barbero bracing(R.E.Brune')
for Flamencos!
Careful planning is what makes a great guitar!

Mc

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Mike Collins

5mm lift+doming might be too much (definitively is for my taste) unless you are OK with a tiny bridge and saddle that give no room for later adjustments.

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Build log

Alex, 'twas to illustrate the math/geometry.

ie. lift + dome = 5mm
5mm lift + 0 dome = 5mm
2mm lift + 3mm dome = 5mm
0 lift + 5mm dome = 5mm

I agree, 5mm neck lift + doming would be excessive.

_________________
Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/

Got it, but an example needs to be ...hmm.. moderate How would it be to read in the driving license manual " [...]you are speeding with 100mph downtown in which case[...]"

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Build log

But that's a dome only on the lower bout, with a flattened upper bout (scooped out solara method?). If you have a fully domed top (25-30') and the neck co-planar to the upper bout, the tangent to the top of the neck and upper bout projected over the saddle position (plus fretboard, frets and action) will not give a 10-11mm string height without a significant tilt to the fretboard. That's just how the geometry is.


Drawn out by hand or using CAD, there's always flattening of the upper bout involved and a taper or tilt to the fretboard on the classicals.

Of course, an elevated fretboard is a game changer!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

One thing I have to say is that no one will tolerate a 4mm action height these days (at least in my experience).
Thus the equation has to be fluid considering what current player's requirements and expectations require.
Lately almost all my clients have hand issues (maybe us geezers are the only ones who can afford custom guitars these days).
So, I'm finding myself dealing wth very critical action heights, neck relief (hurray two way adjustable truss rods) as well as nut spacings not to mention significant customization of board taper to get the desired result.

I found this issue rather intimidating when planning my first guitar since I was going with the traditional construction of building face down on a solera with a Spanish heel and its fixed neck angle.

Laying out the correct geometry on a scale drawing in the planning stage, while being a critical step, still doesn’t seem to get you all the way there if this is the target geometry to arrive at after the guitar is under full string tension. It seems that neck/body/soundboard deflections, wood creep, etc. must also be predicted somehow and allowed for.

Joe

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Mike Collins

Joe, the idea is to set the basic dome, neck, bridge geometry close enough during construction that there is plenty room enough to play with the fingerboard taper, nut, saddle, adjustments to dial in the set up just right.

If you don`t, then there is no way that fingerboard taper or saddle height can accommodate the adjustments that will be required.

Don`t worry yourself silly on your first. Build it as best you can and then study it and learn from it. Build the next one better. Repeat.

_________________
Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/

This seems to come up very frequently
I'm just finishing writing a spreadsheet to do these calcs
Anyone wants a copy Pm me your email

Thanks Douglas. I agree somewhat with the ‘don’t worry yourself silly on your first’ philosophy but in my case it clashes a bit with my compulsive nature and therefore my attempt to build the best I possibly can.

Anyway, I finished my first guitar last year and as it turned out there was very little measurable change in action between unstrung and strung. Can I attribute this in part to the rather robust Hauser soundboard design? Seems I’ve heard others describe fairly significant top/neck deflections with some guitars once under string tension and it was this unknown aspect of the whole geometry issue I had apprehension about, and which still puzzles me.

Filippo, FWIW I use a dummy bridge, nut, saddle and frets, homemade measuring sticks and shims (but no weights) to check neck angle/action prior to installing frets.

Joe