Assessing Classical Neck

[ChrisN]

I think I understand steel string guitars enough that I'm a little confused by what I'm seeing on a '70s Conn Classical C-300 with what I believe is my new favorite neck joint (pics are of another, not mine).

Action is 4.5mm E and 3.5mm on e, which is a bit high even for a classical, but there's enough saddle left to be able to restore 4mm and 3mm pretty easily, but that's not how I do things (though I should).

In checking things out, I found a straightedge laid on the frets hit below the bridge top (at least 1/16"). I then realized that the fretboard was not in a plane - the 12th fret is a rocking point - pressure toward the headstock and the straightedge is raised off of the soundboard frets, and vice versa. Using the straightedge on the soundboard frets (meaning, the straightedge is not touching frets 1-11) and the straightedge hits farther down the front of the bridge (maybe 1/4" total).

I also used a notched straightedge (slots for frets so the straightedge lays on the fretboard, not the frets), and the neck was dead flat (no relief) from frets 1-12, but then was up in the air above frets 13-16 (not touching) due to the 12th fret rocking point.

No truss rod on this guitar.

What do you think is going on with this guitar's body and/or neck that provides a rocking point at the 12th fret, with a flat neck from 1-12? If the guitar was folding up, I'd think the fretboard wouldn't be flat from 1-12 - it'd have a bit of a curve. If the body was folding up (neck stays straight), then I'd think the soundboard frets/board would be pushed up to complete the curve as the soundhole folded in on itself. I should note the guitar plays and appears fine - no bulges or raised areas, belly is nice and flat.

Of course I'll likely reduce the saddle to lower the action a bit, saving the reset for later, but I'm curious if anyone can shed light on that I'm seeing.

[mirwa]

Some people and majority of manufacturers, put the frets into the fretboard whilst its not attached to the neck.

Once you attach the fretboard to the neck, the fretboard sits up in the air over the body, traditionally a clamp is used to pull it down and clamp to the body, we call this in the bizz as fallaway.

Classical necks join the body at the 12th fret as well rather than acoustics which are traditionally 14th, hence the hump happens at the 12th,

I personally fit a fretboard to the completed neck body join, then level it again and then fret up, gives a perfectly straight neck.

Steve

[ChrisN]

Originally Posted by mirwa

Some people and majority of manufacturers, put the frets into the fretboard whilst its not attached to the neck.

Once you attach the fretboard to the neck, the fretboard sits up in the air over the body, traditionally a clamp is used to pull it down and clamp to the body, we call this in the bizz as fallaway.

Classical necks join the body at the 12th fret as well rather than acoustics which are traditionally 14th, hence the hump happens at the 12th,

I personally fit a fretboard to the completed neck body join, then level it again and then fret up, gives a perfectly straight neck.

Steve

I think this is the fallaway you suggest. I saw Roger Knox use the term in another thread, but was unfamiliar with its meaning. This old Conn came out of one of those old Japanese factories like Matsomoku or similar. Probably faster to have separate lines for fretboard prep, neck assembly, etc. than to do it your way.

You say "once you attach the [pre-fretted] fretboard to the neck, the fretboard sits up in the air over the body" - why is that necessarily so just because the board was fretted before being glued to the neck? If the fretted board is glued to the neck (and the extension is then glued to the soundboard) after the neck is assembled to the body, why doesn't the fretboard run in a flat plane, assuming the neck angle is correct? I'm afraid I'm just not seeing why/how the pre-fretting makes the difference, but I'd like to understand, so thanks for your patience.

In thinking more about it, inserting the frets first to an unmounted board would seem to create a backwards bow, as the fretboard was forced into a gradual reverse curve by the frets' insertion. Forcing that now-curved board to be flat again for the glue process to the neck would seem to apply some backwards pressure on both the neck and the soundboard, but is that potentially enough force to result in creating the rocking point at the 12th? I wouldn't think so, given the stoutness of the neck, but I suppose it's possible. In the meantime, I'll read up on fallaway.

Thanks Steve

[mirwa]

The top of a guitar is basically a flat surface, the neck is set into the body at an angle to allow the strings to rise up to the bridge and saddle.

The fretboard continues along the same plane as the neck, then is pulled down to contact the body

When a non fretted board is fitted to the neck and body, it is then planed flat and fretted afterwards, so fallaway does not exist

On a well fretted board, no backbow is introduced from the fretting process, the tang hooks barely add any compression, for compression fretting, we will use say a 24 thou wide tang into a 23 thou wide slot, which will induce backbow.

[redir]

I'm not quite sure what you are describing but the way I build them, the neck actually has forward angle. The straight edge along the frets on my guitars comes probably about 1/16th below the bridge as well. 4.5mm certainly is high action though.

How thick is the bridge?

[ChrisN]

Originally Posted by mirwa

The top of a guitar is basically a flat surface, the neck is set into the body at an angle to allow the strings to rise up to the bridge and saddle.

The fretboard continues along the same plane as the neck, then is pulled down to contact the body

When a non fretted board is fitted to the neck and body, it is then planed flat and fretted afterwards, so fallaway does not exist

On a well fretted board, no backbow is introduced from the fretting process, the tang hooks barely add any compression, for compression fretting, we will use say a 24 thou wide tang into a 23 thou wide slot, which will induce backbow.

I think I get it now - I didn't start with a negative angle for the neck to accommodate string tension, so that's the plane interruption. Both pre-and post-fretted boards have fallaway, it's just that the plane is first restored to the non-pre-fretted board before frets are installed by eliminating the hump.

But, assuming the final neck plane is perfect without tension, isn't it unavoidable that a strung-to-tension neck will have a slight forward bow, thereby eliminating the usefulness of using a straightedge to assess neck angle, since it won't lie flat?

[charles Tauber]

Originally Posted by redir

... the neck actually has forward angle.

As you point out, the "traditional" - as opposed to the modern "cross-over" - classical guitar is not simply a steel string guitar with nylon strings on it. Traditional classical guitars aim for about 11 mm vertical string height from the top to the bottom of the strings at the bridge. This is achieved, traditionally, by having a less than 180 degree neck angle - call it "forward" or "negative" - as opposed to typical steel string construction that achieves its 1/2" or so string height at the bridge by having a greater than 180 degree neck angle.

Likely, what you are describing - two planes in the fingerboard - is as Steve described, fallaway. On more expensive instruments, the much greater amplitude of the nylon strings was dealt with in a few different ways, one of which was to contour the playing surface of the fingerboard from nut to sound hole, so that the fingerboard was not "straight", particularly on the bass side.

[charles Tauber]

Originally Posted by ChrisN

I think I get it now

Doesn't sound like it.

- I didn't start with a negative angle for the neck to accommodate string tension, so that's the plane interruption.

No, the neck angle is set to achieve the desired vertical string height from the top to the strings at the bridge. The neck angle is not there to accommodate distortion of the neck/fingerboard under string tension. (The neck angle should allow for small distortions of the top that lifts the bridge under string tension.)

Both pre-and post-fretted boards have fallaway, it's just that the plane is first restored to the non-pre-fretted board before frets are installed by eliminating the hump.

Install a flat fingerboard, glue and clamp. Then plane it "flat" from nut to sound hole. Then fret it. Doing so eliminates any deviations from a single plane. "Fallaway" is not a given: some purposely create fallaway, others avoid it. Fallaway is intended to give greater clearance to the upper notes on the fingerboard, but makes the strings more difficult to fret by increasing the distance from the un-fretted string to the fret. Those who regularly play in upper-most frets, generally, don't want fallaway. Those who don't venture much beyond the fifth fret don't know or care one way or the other - having fallaway allows the maker/repair person to ensure the strings won't buzz beyond the neck/body juncture (upper frets).

But, assuming the final neck plane is perfect without tension, isn't it unavoidable that a strung-to-tension neck will have a slight forward bow, thereby eliminating the usefulness of using a straightedge to assess neck angle, since it won't lie flat?

The straightedge test isn't particularly relevant for (traditional) classical guitars. Even on steel string guitars, it is only a quick indicator of the geometry of the instrument.

[mirwa]

Originally Posted by ChrisN

assuming the final neck plane is perfect without tension, isn't it unavoidable that a strung-to-tension neck will have a slight forward bow, thereby eliminating the usefulness of using a straightedge to assess neck angle, since it won't lie flat?

As far as unavoidable neck bow, that is a whole different kettle of fish, so many factors influence.

Start with a quarter sawn block of wood for a neck 2 inches wide by 1 inch thick, put some strings on it and no way in the world is it going to move from the tension of the strings, now start shaping it into a neck, as we remove wood for comfort we also remove strength to combat strings, at one point the remaining wood is not strong enough anymore, so now we fit a truss rod or compression fret.

Bowing of the neck is subjective to wood grain, wood type, neck profile, fret fitment style, fretboard material, trussrod etc etc etc.

Steve

[ChrisN]

Originally Posted by redir

I'm not quite sure what you are describing but the way I build them, the neck actually has forward angle. The straight edge along the frets on my guitars comes probably about 1/16th below the bridge as well. 4.5mm certainly is high action though.

How thick is the bridge?

Bridge (slopes, so measured at saddle) - 11/32 (8.72mm, .343")

E String is 1/2" (12.7mm) off top

Exposed Saddle measures 1/8 in middle 5/32 on E and 7/64 on e. I think there's enough room for me to take 1mm off to reduce the action to something more acceptable, say, 4mm E and 3mm e (which I understand are pretty typical measurements for this type of guitar). Do you set yours up lower than that? If so, to what?

Does your straightedge run along a flat/consistent plane? Or on one of the slopes of a fallaway? If the latter, which slope gives you the 1/16" mark?

[ChrisN]

Originally Posted by charles Tauber

As you point out, the "traditional" - as opposed to the modern "cross-over" - classical guitar is not simply a steel string guitar with nylon strings on it. Traditional classical guitars aim for about 11 mm vertical string height from the top to the bottom of the strings at the bridge. This is achieved, traditionally, by having a less than 180 degree neck angle - call it "forward" or "negative" - as opposed to typical steel string construction that achieves its 1/2" or so string height at the bridge by having a greater than 180 degree neck angle.

Likely, what you are describing - two planes in the fingerboard - is as Steve described, fallaway. On more expensive instruments, the much greater amplitude of the nylon strings was dealt with in a few different ways, one of which was to contour the playing surface of the fingerboard from nut to sound hole, so that the fingerboard was not "straight", particularly on the bass side.

That makes sense, especially with my forward bow, relative to the bridge - that suggests the neck angle is OK.

Originally Posted by charles Tauber

Doesn't sound like it.
No, the neck angle is set to achieve the desired vertical string height from the top to the strings at the bridge. The neck angle is not there to accommodate distortion of the neck/fingerboard under string tension. (The neck angle should allow for small distortions of the top that lifts the bridge under string tension.)

Install a flat fingerboard, glue and clamp. Then plane it "flat" from nut to sound hole. Then fret it. Doing so eliminates any deviations from a single plane. "Fallaway" is not a given: some purposely create fallaway, others avoid it. Fallaway is intended to give greater clearance to the upper notes on the fingerboard, but makes the strings more difficult to fret by increasing the distance from the un-fretted string to the fret. Those who regularly play in upper-most frets, generally, don't want fallaway. Those who don't venture much beyond the fifth fret don't know or care one way or the other - having fallaway allows the maker/repair person to ensure the strings won't buzz beyond the neck/body juncture (upper frets).

The straightedge test isn't particularly relevant for (traditional) classical guitars. Even on steel string guitars, it is only a quick indicator of the geometry of the instrument.

That's useful information, and it explains my fallaway on this lower-end student guitar. Thanks Charles.

I'm very surprised at this guitar's sound - very rich bass and clear/distinct trebles all in one box. Very light construction means you feel every note. Probably doesn't sound that great as you move up the board, especially with the current intonation compromise (hight action), but to my rookie ear, it's enjoyable.

[redir]

Originally Posted by ChrisN

Bridge (slopes, so measured at saddle) - 11/32 (8.72mm, .343")

E String is 1/2" (12.7mm) off top

Exposed Saddle measures 1/8 in middle 5/32 on E and 7/64 on e. I think there's enough room for me to take 1mm off to reduce the action to something more acceptable, say, 4mm E and 3mm e (which I understand are pretty typical measurements for this type of guitar). Do you set yours up lower than that? If so, to what?

Does your straightedge run along a flat/consistent plane? Or on one of the slopes of a fallaway? If the latter, which slope gives you the 1/16" mark?

I don't particularly care for fall away myself. My understanding of it is that it is initially designed like that so that when the guitar starts to fold up under string tension the fall away will become flat and as such the guitar will no longer have fall away. The idea being that if no fall away is added then when it folds up you will have the opposite problem.

I've jsut not experienced that and in fact as you get closser to the saddle frettign notes up higher on the neck the angle the string makes from the fretted note to the saddle is greater which means you are less likely to get buzz anyway/

So I just don't really 'get' the concept of fall away. I like to see a straight shot from the nut to the end of the fretboard, relief notwithstanding.

Personally I like my classical guitars set up with what I call concert action, 5/32 under the low-E down to 4/32 under the high. It produces the loudest and clearest notes and that's the way I like it. A lot of players however are willing to give up clarity and power for ease of play. So it's purely a matter of choice.

Your bridge thickness sounds about right. It also sounds like you have some room to play. If the saddle is out 1/8th in the middle then you should have plenty of room. I'm guessing your fretboard is arched but that doesn't matter even at the ends you have room.

[ChrisN]

Originally Posted by redir

I don't particularly care for fall away myself. My understanding of it is that it is initially designed like that so that when the guitar starts to fold up under string tension the fall away will become flat and as such the guitar will no longer have fall away. The idea being that if no fall away is added then when it folds up you will have the opposite problem.

I've jsut not experienced that and in fact as you get closser to the saddle frettign notes up higher on the neck the angle the string makes from the fretted note to the saddle is greater which means you are less likely to get buzz anyway/

So I just don't really 'get' the concept of fall away. I like to see a straight shot from the nut to the end of the fretboard, relief notwithstanding.

Personally I like my classical guitars set up with what I call concert action, 5/32 under the low-E down to 4/32 under the high. It produces the loudest and clearest notes and that's the way I like it. A lot of players however are willing to give up clarity and power for ease of play. So it's purely a matter of choice.

Your bridge thickness sounds about right. It also sounds like you have some room to play. If the saddle is out 1/8th in the middle then you should have plenty of room. I'm guessing your fretboard is arched but that doesn't matter even at the ends you have room.

Thanks for that info - my current action's not that far off, I double-checked and E is 4mm (smidge above your 5/32 that is 3.97mm), and e is 3.5mm (smidge+ above your 4/32 that is 3.18mm). It sounds great, but it feels to this rookie like walking across power lines, as high as those strings are. I guess I'm a low-action guy at this stage, but I don't want to push this classical too far and get buzzy.

I also don't seem to have the neck joint I showed in the pics above. Mine's a higher end model and it appears to use some form of modified Spanish Heel joint. Mine does not have the heel bolt, or the full block under the fretboard extension for that sliding dovetail joint shown. But, neither does mine have the full "U" of the typical Spanish Heel. Instead, mine has a half-a-"U" from under the extension to the back, where it stops. Any idea what kind of joint that might be? If it helps, mine's supposed to be a copy of a "Jose Ramirez 1A".

[charles Tauber]

Originally Posted by ChrisN

mine has a half-a-"U" from under the extension to the back, where it stops.

That is the traditional "Spanish heel" arrangement. There are lots of variations including dovetail and mortise and tenon arrangements that use a similar shaped interior block. I use the "U" shaped block with a dovetail joint. I used to use a Spanish heel/non-joint arrangement with both classical and steel string guitars. I don't anymore. I see no advantage to it - unless one is building entirely with hand tools - and some disadvantages.

[ChrisN]

Originally Posted by charles Tauber

That is the traditional "Spanish heel" arrangement. There are lots of variations including dovetail and mortise and tenon arrangements that use a similar shaped interior block. I use the "U" shaped block with a dovetail joint. I used to use a Spanish heel/non-joint arrangement with both classical and steel string guitars. I don't anymore. I see no advantage to it - unless one is building entirely with hand tools - and some disadvantages.

That's what I was afraid of, as it limits reset options to back slips and bolt-ons, and I was getting pretty comfortable with that vertical sliding dovetail arrangement, but that's fine. Luckily, this one appears to not need a reset so I'll just drop the saddle a bit and enjoy it as it approaches its 50th birthday. Thanks for the info.