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I wanted to build a 12 string guitar-- then got the archtop bug & built one. Had a thought the other day that (since I already have the wood) I could build my second as a 12. Any reality in that thought? Any major list(s) of problems I will encounter?

Jimmy D'aquisto built one-there's a picture of it in the book "Acquired of the Angels"

Yeah thats using the old nogin! A 12 string archtop would be "capital C" C-o-o-l!!
Man dont neglect us the build photos if you decide to go that route!
Cheers
Charliewood

Here's a pic of my first
BUT, can anyone tell me which concerns I should have about:
bracing
neck - aditional brace?
top- thicker braces?
how to deal with the wider bridge?
what about a beefed up taail piece?
etc.
Phil

find the formula for downforce

find sting cacl @mimf links

plug in values

use your best judgement?

I personally might go a little 32nd to 64th thicker on the recurve but ianaly (I am not a luthier yet)

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"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

Come to think of it I would prob. go thick around the F's also.

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

I'm hoping that the lack of response is because your first looks like you have a decent understanding of the issues involved & nobody that has actually built an arched 12 (or knows some one who has to ask) has seen this thread.

I think a lot of people use carbon fiber rods to help the neck extension. I do not see a problem with them running the full length of the neck if you need reassurance. My epi flattop 12 only has a truss rod and is holding up fine. For the headstock I might be tempted to do some sort of cut out to keep weight where I felt it belonged.

found my notes

Downforce

F = Tx2xsin(a/2)

F= down force on top
T= string tension in pounds
A= break angle

String cacl will give you tension
plans determine break angle at bridge

use a bathroom scale to push down on to get FEEL of downforce
Give it your best thought out shot.

I have not built an archtop yet just step top dulcimers with strategic thinning. I just try to think about the issues to the best of my abilities and hope tone faerie lead me in the right direction.

Well I hope some one who has archtop experience will chime in cause I'm starting to feel like a thread killer.

with humility, Kirby

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

Hey Phil,
I'd say go for it!
Most 12 string sets are lighter gage than medeum 6 strings so it's not like the forses are doubled realy. If I had to guess, maybe you could make slightly taller X braces but likely do not need to change much. It's like putting heavy gage strings on your first.
I think..

Wade

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Wade
Nashua, NH
http://www.wadefx.com

So: KO what kind of truss rod did you use? I just used the 3/16" stainless kit from stewmac on my last-- Was a little concerned about the peened end-- May use a two way in the next. Built my own for the mandolin out of standard 3/16" steel & bent it to go into a hole in the heel. The carbon rods sound good-- Might make the pucker factor slightly less.
Wade-- Thanks- I did not know that 12 string sets were lighter than normal (medium) string sets. I like extra lights on my stuff anyway-- Have to replace sooner, but they work for me. besides, I think they are easier on the instrument & I play really hard when strumming & they sound good & don't have to be driven as hard (with my o'l fingers) in fingerstyle. I need to look up the specs on a standard 12 string set.
It's WAY to friggin cold in the shop in N Texas to do anything but shiver ( have to get a good heater) So this is all speculation right now-- The wood & tools are waiting for warmer. Just the right time to haul out the guitar & mando & pick-- Maybe write a little-- Maybe the lack of response to this is that most other folks are doing just that -- Pickin & writin or grinnin-- maybe all three

Phil, for starters I would start with calculating the likely lateral force and downward force on the bridge from the gauge of 12 strings you are likely to use.

How "wed" are you to using the 4.5 degree neck angle or 1" bridge height if you followed the Benedetto plan.

An interesting set of calculations would be to calculate the downward pressure on the top plate at the break angle you built your first one. Substitute the pressures from a 12 string and then calculate how much change is required in the break angle to maintain the same forces as witnessed in a 6-string.

That is where I would start before asking how thick the plate, recurve etc would have to be.

Sorry for the missunderstanding EPI is short for Epiphone aj 15-12. Have not had to use any truss rod adjustment yet so I have not checked to see what kind it is.

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

You know In me head I have been working on an adjustable break angle tail piece but when I draw them they are ugly. I'll get it though. I just thought it would be a great way to fine tune the response of any given top.

Anthony now I want to build one to find out where the line is on overall downforce vs single string downforce and the effect on string to string clarity and separation.

Man I love this hobby so many ways to build a sound and then ya tweak it to that particular piece o tree.

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

I have heard a trick po 12 stingers use is to capo 1 and tune down a 1/2 step to help keeping the top from dippin an bulging on a flattop. Relevant?

Not really except as a reminder to think in terms of trades offs?

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

where is the main concern for lateral force? heel block recurve area thickness?

I have a rover rm75 with center seam seperation and very slight buckling in that area>

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

oops I meant. .

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

I think that means I will have to splint it rather than just close it but I could be wrong.

Moral, You do have to think about lateral forces.
I think?

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

Issues my guitar has issues!!!
aI think I willshut up now I dont even know if my formula is one of the half right ones?

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

I try to finger pick My 12 but they really shine on some chords.

I wonder where an arched 12 will shine.

I talk to much.

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

I do daddad on a 30 dollar cheapie with a 9/16 and hope it sounds like swamp rock!


OR

Ovation banjo country>

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"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...

Any way some years ago found the equation I think it was a statics book and then I found an instance of some one using it. So I do think it is right. My math experience was just barely enough to draw lines and curves and understand how to compress data using Borland C++.

That was in the early 90's and my mind does not work near as well any more so does someone know if I have the equation right?

_________________
"It's a Tone Faerie thing"
"Da goal is to sharpen ur wit as well as ye Sgian Dubh"
"Sippin Loch Dhu @Black lake" ,Kirby O...