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Greetings guys!

So. This has been a project that has slowly been moving forward over the past year, and now that some of the people involved are on vacation and can actually work on it, i figured id ask some questions where i lack the knowledge. I use a CNC, but, my questions here are more for the wood/design aspect.

My brother is quite the bassist. Normally rocks a Warwick 6 string Corvette but when occasion calls, he grabs his Galveston 8 string, and 2 hand taps. Guy has even filled the spot when we're down a guitar player. Anyways, ever since i built my 4 axis CNC a few years back hes been on me for a 12 string extended range.

We have built it in Solidworks, test cut it out of pine, and he picked his woods. Its White oak and black walnut. I've had many guys tell me this is a bad idea, and probably is, but, its already been laminated and glued for the neck. I figure we'll run with it for now. My best friend helping me with this comes from a family owned wood press/bend shop, so, having it all glued and pressed together wasnt an issue.

Heres the design: (i know, the headstock holes need moved)


The different colored rectangles are the stock, white oak and black walnut. Although the outter body slabs are now going to be white oak.

And heres the test cut



Now for the questions i have:
Length: My bro has this for a 36" to 34" fanned fret setup. Are we even going to be able to find strings this long?? Moreso towards the headstock side where the strings go real far from the nut.

Neck attachment: I was showing off my skills at running my own machine more than thinking about the final product. I COULD do neck through design, as this was cut in the test. However, this requires 6 different machining positions, all of which have to line up perfectly, all of which can't have a single failure. Granted my screw ups are far and few in between, this fact has me thinking of going bolt on. Especially since its mostly 2 hand tapped, and i know from experience how much I can improve the action of even the cheapest of guitars by playing with the neck pocket and angles.. Is there a calculation for the pocket? IE how much material should i have neck and body mating? Does this also play into my above question of length? Way i figure it too, say one part succumbs to what everyone's telling me on the wood choice being poor, i still have the remaining (ie neck is terrible i still have the body)

Truss Rods: His 8 string has dual trusses. My Shecter 8 does as well. Its not too difficult to give mine a good setup, as theyre located right next to each other. His 8 on the other hand is a forever ordeal, as they are spaced quite far apart. So, when adjusting, i always have to watch out for things becoming uneven. It was suggested to me i go with carbon fiber rods and one truss in the center. Thoughts? How about diameter? I have my own lathe and access to a mill, so, i just assume I'm making my own. I would lie to be able to adjust bend like a regular bass, as i know he will stop and play it like a normal bass, especially in a live setting rather changing instruments.

Neck Scarf joint: Do i need one? Or should i say, is it stronger? I have an old 1960's kay that doesnt have one. The headstock lies flat, and the strings are angled under a bar just after the nut. The past guitar i did though, we had a slab of walnut that was tall enough for me to mill it all as one giant piece. Id have my wood working buddy do it.

Anyways, once it's machined, the neat part i've never done is going to be the pickups. One of the engineers i work with has built several over the years, and I'm going to have him design them. I'm going to use either my lathe, or the rotary axis on my cnc to do the winding. The inner plastics will either be milled or 3D printed, i havent decided yet.

The bridge will be milled. Possibly by me manually, or, by a handful of machinists i know if they get slow. Havent decided 100% on what metal yet, my brother and i keep arguing over finish. He wants the finish to match the tuners. Im guessing i can find a shop here that will chrome/powder coat to match, but, i know i need to be close on what type of metal my bridge is.

The overall goal here guys is to have a functioning 12 string bass. If we break something in the process, we learned something. I'm doing what i can to make sure this goes smoothly as possible to be a final product I'm proud of, and more importantly, one my brother loves to play.

Thanks guys. Any input is appreciated.

I would keep it as a neck through design. Bolting on a neck that wide will be difficult to make it secure and stable enough.

The horns on the body look too thin. They need to look beefier to visually balance with the neck.

Definitely use carbon fiber rods in the neck. I made a six string bass guitar and used one truss rod with four carbon rods which turned out making the neck too stiff. If I were to do it again I would use one really strong truss rod and two carbon rods set out halfway to the edge of the neck.

This will be an interesting, but a challenging build. Is it your first?

As far as scale length and strings.... I seem to remember someone making a 37' scale bass, but I don't remember who made the strings. I'll see what I can find out.

Neck attachment - bolt on will be fine, just space them out for stability. Dual truss rods - YES! You need to be able to adjust both sides of such a wide neck.

Pickups - lots of market choices already. I'd go with Bartolini's.

One suggestion... this thing will be neck heavy. Extend the top horn out much farther for balance, or you'll regret it.

Rock on with your bad self.

_________________
"Act your age, not your shoe size" - Prince

I'm interested in how much tension there will be between the head and bridge.

_________________
wah
Wah-wah-wah-wah
Wah

Kalium Strings specializes in extended range bass & guitar strings and offers lengths for instruments with up to 40" scales.

http://store.kaliumstrings.com/index.php/f-a-q.html

Have a look at the site and especially the details on string winding length and nut-to-tuner lengths to see if your headstock design is compatible. I have no doubt they can accommodate you but you still need to be careful when ordering.


A big question for 12-string instruments is tuning, especially on the high side. Do you have the tuning planned out yet?

With a 34" scale the highest note you can tune to reliably is D4 (the D two octaves above the open D string of a 4-string bass.) Eb4 is also possible, especially if you don't want to do any bends on that string, and some brands will outlast others.

If you start with Eb4 as the upper limit and want to tune in 4ths then your open strings would be:

1 Eb4
2 Bb3
3 F3
4 C2
5 G2
6 D2
7 A1
8 E1
9 B0
10 F#0
11 C#0
12 G#-1


That low G# is an octave and a semitone below the lowest note of a standard piano which is A0. It is very difficult to amplify that note with standard bass gear so it is of questionable utility. Another way to think of it is that it's more than an octave below your low B string (B0).

All that said, 12-string basses certainly exist, I think I've seen about 10 or so in my internet wanderings, and they're enjoyed by their players and can be fantastic for two-handed playing.

My favourite player is this guy, Scott Fernandez, who indeed rocks his bad self!




One more thought: the bigger the fan the better when you're trying to accommodate such extreme range. If it was me I'd go for something like 40" - 29" for a much more balanced tone throughout the range.

Keep us posted!

Leo

Of course i have 2 conflicting answers on bolt on vs neck thru. The problem is i value both opinions.



I am too. I know it can be calculated.

Horns for balance, not just visually but weight wise too?

Durero, lowest he wants to go is F#0. Even now we have problems reproducing that. Works great on a DI Box recording, but, i think maybe once were we ever able to reproduce it well live. Basically had to run a DI box to amp AND PA system with a sub. He usually frets it though, so not too many open F#0's. Looking to encroach more into the guitar range. That being said, i take it a shorter scale length/bigger fan ratio is in order? Figure we start at F#0,

01 Db5
02 Ab4
03 Eb4
04 Bb3
05 F3
06 C2
07 G2
08 D2
09 A1
10 E1
11 B0
12 F#0

Any thoughts on scarf joint/Head angle?

This isnt my first build. First build is here
viewtopic.php?f=10130&t=46642&hilit=black+walnut

But isnt complete yet. Waiting on wood press guy to give me a design for inlays before i cut the fingerboard. Why can't my first ones be a simple Tele? Both guys wanted something off the wall and very CNC time consuming!

Regarding tuning, you're running up against the laws of physics and limits of steel string strength to weight ratios for your highest strings.

If your brother is not willing to add strings below the low F#0 then you face the following design choices as I see it:

1. Keep the current design with the 34" high string scale and reduce the number of strings to 10 because the high Ab4 and Db5 are not possible at that scale.

2. Redesign for 11 strings with a 36" - 25.5" fan with the F#0 to Ab4 tuning.

3. Keep 12 strings but use the Fretfind2d website to show your brother how extreme a fan is required for the tuning he's asking for. 19" is the maximum scale length for Db5. Does he really want a 36" to 19" fan? You'll find it would require a redesign of the body to accommodate such a short string on the treble side of the neck.

Here's a link to a 12-string fretboard which could handle that tuning.


How is the 19" scale length number for Db5 obtained? I've done my own extensive testing on the limits of high tunings for steel strings, and there are numerous others who've come up with similar findings. To use 34" scale bass as the test bed, you can try various strings of different gages and brands and the upper limit is D4 for a reliable lasting string which might stand a bit of string bending. Eb4 can be achieved with the strongest brands and is pretty delicate but useable.

The only way to get higher is to shorten the scale length.
The 5th fret of a 34" scale Eb4 string gets you to Ab4 and is at the 25.5" scale point.
The 10th fret of a 34" scale Eb4 string gets you to Db5 and is at the 19" scale point.


I hope this info is helpful.
Cheers.
Leo

Durero i think i mispoke when i said Db5. Shouldnt it be Db4 to be in guitar range? I only jumped from 4 to 5 as it did in your earlier post from A1 to D2. I'm not looking at an octave layout as i type this. Sorry man. Darn! I redrew this before i saw your reply. Email isnt getting the notifications.

I used fretfind2D actually this and last time around. Totally tore the 3D model apart, set it up for bolt on. What I love about this site, is i could download the .DXF file and open it right up in my CAD software. Its not a closed model on the frets, but, it had the points in place that allowed me to close em up. So here's what I've got, 36-28", only for the fact I've seen some Ibanez 8 and 9 string guitars this length. But, I'm guessing i may need to increase the fan even more no?

Anyways. Heres where the CAD currently lies:
Top Down with the strings/frets ghosted on the design


Transparency on fretboard to show the truss cavities


Neck Pockets



Now I'm guessing i have the fretboard drawn way too thick at 3/8", but, i wasn't really intenting on a radius at all on this fretboard. Any input on that idea? His 8 is pretty flat.

Since I'm paranoid about the neck/scarf joint, i added this little blob


Which will sand out much better than i can draw it in parametric CAD software.

I'll come back with dimensions once I've got this honed in a bit better, and once the debate with my bro and the fan radius is complete.Now that i have it broken apart for bolt on, its actually pretty painless to have it redone for a different fan.


Thanks again everyone.

Yes Db4 is in the guitar range (E4 is the high string of a standard-tuned guitar) but if that's what he wants as his highest string then that pushes all the strings down an octave leading to a low F#-1 as the 12th string.

Something's got to give.

The player has to accept a low F#0 string with a high Db5 and fan down to 19", or a less extreme fan with 1 or 2 more bass strings tuned below the F#0, or a reduced number of strings.

As the builder you may have to force the player to sit down and write out the tuning he wants for each of the 12 strings.

It's easy for an ambitious player to just say "I want a 12-string bass." but such an instrument tuned in 4ths with 24 frets results in a 79 semitone range which is not far from an 88-key piano, and piano's have much bigger "fans" than anything we've discussed here yet.

If the player insists that tuning below F#0 is unusable, and doesn't want an extreme fan, then he's actually asking for a 10 string bass.

Happy arguing!

Regarding the octave numbers, I'm following the convention of scientific pitch notation in which the octaves start at C.

So you were correct in your earlier post regarding the jump from Ab4 to Db5. Going from Ab4 to Db4 would mean jumping from Ab4 down to Db4, instead of up to Db5.

Sorry for the delay guys. Work sent me out in the field.

Well, for starters, i didnt realize ALL of his bases are 34" scale length, even his 8.

I'm guessing if i made that my starting point, the low G#0 and C#0 would be pretty sloppy.

Actually looking up the reference to middle C, i screwed up. I had put G2 ->C2. Should be G2- C3

Yup. I am seeing your point on fighting physics here.

Scott Fernandez goes over his 12 string without a fanned fretboard (holy crap!) he goes C#, F#, B, E, A, D, G C, F Bb, Eb, Ab, with the Ab being a .007 string. Wow. Smallest i've ever went is .008 on an old hollowbody from the 60s, and that was a nightmare to keep from breaking.