Solera functional dimensions

Construction and repair of Classical Guitar and related instruments
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memit
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Solera functional dimensions

Post by memit » Fri Jul 28, 2017 1:07 pm

Sorry for asking such a stupid (!?) question. I need to understand how this works.

In Bogdanvich's book (Classical Guitar Making pag. 56) I found this:
2,5 mm under the solera level at the nut position and aprox. 2 mm OVER the solera level at the brige position.


Image

In Courtnall's book (Making Master Guitars pag. 165) I found:
3mm under the solera level at the nut position and aprox. 2 mm UNDER the solera level at the brige position.

Image

It looks to me that for the same dimensions of the bridge+saddle, will result in a very big difference in action beetween the two approaches/models.

Thank You for any kind of opinion/answer.
mihai,

John higgon
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Re: Solera functional dimensions

Post by John higgon » Sat Jul 29, 2017 10:32 am

Not a stupid question at all! Unfortunately, I am not sure of the answer, but I think I recall reading that the Courtnall neck ramp measurement is a mistake, and it should be closer to 1.5mm - IIRC. Also, the dimensions of the fretboard may make a difference, i.e. the fretboard may be an even thickness along its length, or thicker at one or the other end. I'm sure others will be able to explain it better, though.

John higgon
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Re: Solera functional dimensions

Post by John higgon » Sun Aug 06, 2017 12:39 pm

Another way to think about this is to start with the desired action - for example, 1mm above the first fret, 4mm above the 12th fret. Doming of the lower bout is typically around 3mm and you are aiming for the top of the saddle to be around 11mm or 12mm higher than the soundboard. All of these are ballpark figures, and some makers will work to their own figures. Anyway, the point is that you can use these figures to calculate the neck angle and / or the tapering of the fretboard. Final setting up will probably involve some minor planing of the fretboard or adjusting of the saddle height. when doing the maths, do remember to include the height of the fret along with the thickness of the fretboard. 😉

Dave M
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Re: Solera functional dimensions

Post by Dave M » Mon Aug 07, 2017 5:08 pm

First you are quite right to be concerned on this. Getting the geometry right is not particularly easy but is very important. Trying to fix it later can lead to bridges which are either much too low or too tall. I have been there!

There has been quite a lot of discussion on this forum with a strong suggestion that the 3 degrees in the Courtnall book is too much.

This is one of the topics:

viewtopic.php?f=11&t=93356&hilit=courtnall+ramp

If you search for Courtnall ramp you will find several discusssions which should help.

Good Luck
Dave

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Re: Solera functional dimensions

Post by Dave M » Tue Aug 08, 2017 8:34 pm

I have been looking at John's book and watching his videos on this. I think that he is saying that he is dishing the lower bout to the point where the saddle position is actually pretty much at the level of the solera. His additional material below the saddle position is going to slope the top down below the saddle towards the bottom of the guitar. ie reducing the depth of the guitar at the butt compared to the waist. This will not affect the geometry of the strings, fretboard, saddle.

So this starts looking more like Roy's jig but with somewhat less backward tilt of the neck.

I may have this wrong and I am sure there are people on the forum better qualified to talk about this.

I personally, as an amateur builder, now use a bolt on neck design as in Trevor Gore's work, but getting that neck/body geometry is still tricky and needs to be right.
Dave

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memit
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Re: Solera functional dimensions

Post by memit » Mon Aug 14, 2017 11:39 am

Thank you, I appreciate all your answers !
mihai,

Jim Kirby
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Re: Solera functional dimensions

Post by Jim Kirby » Mon Aug 14, 2017 12:03 pm

The ramp on Bogdanovich's lower bout is very similar to how Jose Romanillos shapes this area. Jose's process, with the top cut to fit inside the unprofiled sides (which have a flat edge and sit on the flat solera outside of the ramp) is a lot easier than the profiling needed in John's process.
In any event, as hinted at above, you need to draw a reference line and then establish what the nut and saddle positions are, what the layout of the fretboard is to get the right action, and how high you want the saddle above the soundboard. Once you get these relative positions established, the entire assembly can be moved/rotated/et w/r the referenc plane to suit your building tastes, and this in turn establishes how you would shape the solera. There are going to be differences in everyone's soleras.

There is a simple formula that does the math for all of this, but coffee hasn't kicked in yet and I can't remember it. I'll look later.
Jim Kirby
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memit
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Re: Solera functional dimensions

Post by memit » Tue Aug 22, 2017 6:45 am

Thank You Jim Kirby !
mihai,

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geoff-bristol
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Re: Solera functional dimensions

Post by geoff-bristol » Tue Aug 22, 2017 11:47 pm

Its worth doing your own drawing - full size. Its interestingly complicated ! Especially when you start to dip the sides of the top or lower bout. Also bear in mind that the board can taper - and also can dip toward to low E side - which makes thing even more complex.

My current workboard has a 4mm dome - across - but only 2mm dome relative to the soundhole - and 3mm relative to the end bout. ie - the sides dip 2mm at the lower bouts - and 1mm at the end. The neck has 1mm raise - but it could be level really.

mitch lees
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Re: Solera functional dimensions

Post by mitch lees » Wed Aug 23, 2017 7:58 am

I have built 2 guitars using the Bogdanovich method, using his later 'upper bout angling insert' amendment rather than that shown in the book. I found that the actual dome produced at the bridge was less than I had planned for, possibly because of 'spring-back' of the bracing which is flat and not shaped. In Rik Middleton's book 'The Guitar Maker's Workshop', he suggests that the spring-back is about 50% and so he constructs the bridge dome in dish hollowed out to twice the depth of the required dome height, and he also argues that if the dome is constructed properly there is no need for any neck angle and the method produces a more robust sound board, or, I suppose, allows the sound board to be slightly thinner for the same strength.

I like the idea of no neck angle as I have worried about making the side slots in the head vertical and using the back when glued on to hold-in the desired neck angle - should the slots not have the same angle as the neck (this would make cutting the side slots much more difficult) ? I have been told by more experienced builders on this site that the angle is so small that I should not worry about it! So I don't - I think!

Anyway, I have decided with the next build to adopt a Bogdanovich/Middleton compromise. I am aiming for no neck angle (obviously), a 2.5mm dome at the bridge and the tilt of the lower bout as per Bogdanovich. Consequently I am going to make the depression in the work board double the required dome, ie 5mm.

I hope this has not complicated what I consider to be an already complex issue.

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Waddy Thomson
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Re: Solera functional dimensions

Post by Waddy Thomson » Fri Aug 25, 2017 3:55 pm

One other thing to think about is, when gluing your back on, do not put too much clamp pressure on the Spanish foot. If you do, you'll get a bit of spring back in the neck, which will change the natural angle that is built into the solera. Always clamp the neck down when fitting sides to neck and gluing the back, and just put enough pressure to make sure there is good contact - back to foot. Doesn't take much pressure to do that.
Waddy

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mitch lees
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Re: Solera functional dimensions

Post by mitch lees » Fri Aug 25, 2017 8:34 pm

Waddy,

Thanks - I had not considered that aspect at all! In fact I think I used a reasonable amount of pressure on previous builds although I did have a clamp holding the necks down. I have now started building my flat-tops with a Spanish foot so it applies here as well (only done one this way but I prefer it to the dovetail).

I measured my most recent classical where I had aimed for a dome of 2 - 2.5 but barely achieved 1mm despite keeping all braces under pressure in a go bar cage while the glue dried. In the end by a small saddle adjustment I was able to achieve the desired action, but it would have been better to get it as the plan.

I am working on an App which will take in to account all the variables (all of those I can think of anyway) ie dome, bridge, saddle, neck angle (+/-), fret board at nut and 12, fret, nut slot heights etc, scale length and hopefully give a read out of action at 12 for any given set of parameters. I embed a substantial carbon fibre rod in my necks so a I am assuming there will be no change in neck angle with string pressure - this may not actually be the case but we will see. If I can get it running I will post it so it can be scrutinized by those better at the maths and programming. The equation seems to work but getting it into an App will be more tricky! If this already exists please let me know and I can get back to clearing the backlog of repairs.

Mitch

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Re: Solera functional dimensions

Post by simonm » Fri Aug 25, 2017 8:51 pm

FYI. The Romanillos' book includes a detailed plan of one of his soleras. It is a a bit different to he run of the mill as his assembly procedure is a variation on the typical Spanish plan but it works very well.

mitch lees
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Re: Solera functional dimensions

Post by mitch lees » Sat Aug 26, 2017 10:22 am

I cannot find a copy of the Romanillos book anywhere - any ideas please?

Mitch

Dave M
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Re: Solera functional dimensions

Post by Dave M » Sat Aug 26, 2017 5:35 pm

Abe books is often good for these things. They are not listing it but it could be worth asking them if they can get it.
Dave

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