Acoustic Guitar Construction

kencierp wrote:Let's get a good angle measurement of the neck heel -- place the neck on a flat surface, place a square along the cheek -- what's the height of the heel and the length of the gap between the square and the cheek?

There are two locating pins screwed into the neck for the fretboard, preventing it from sitting totally flat. That shouldn't matter though?

Heel length is 3.06". I'm not really seeing any measurable gaps between 1 cheek & the square (appears to be 90 degrees). The other side has very slight gap of, maybe 3/4" long...very minimal at best & almost square.

Could it be that he forward part of the neck block (near soundhole) is higher than where it is at the sides, causing the top to rise up some under the fretboard throwing the plane off?

Hmmm...from watching the Martin tour Vid:

Flat sanded for the top & sanded just slightly arched for the back...

TonyinNYC wrote:Good thing it isn't a dove tail neck! You came to the right place to get this sorted out and Ken and Dave have already pointed you in the right direction.

No worries Tony. I have a Dovetail Deep-body OM right behind this one, that's had me even more befuddled longer than this one...sigh

Bingo -- glad you noted that comment on the Martin video and as you can see their sanding machine is designed to do exactly what Chris mentions -- over the years I have had much conversation and email exchanges with the guys at the Martin factory regarding this process and the goal. Mark Brickert indicated that until the dawn of the cutaways when players actually stated using the upper registrars the hump at the 14th fret was really not much of a concern as long as there was no buzz!!

Anyway, drill a couple of holes in a board that correspond to the locators on the neck so you can get an accurate measurement. Its important so we can proceed with a real plan of attach. You will also want to make a fingerboard simulator as described -- note it too has the clearance holes.

kencierp wrote:Bingo -- glad you noted that comment on the Martin video and as you can see their sanding machine is designed to do exactly what Chris mentions -- over the years I have had much conversation and email exchanges with the guys at the Martin factory regarding this process and the goal. Mark Brickert indicated that until the dawn of the cutaways when players actually stated using the upper registrars the hump at the 14th fret was really not much of a concern as long as there was no buzz!!

Anyway, drill a couple of holes in a board that correspond to the locators on the neck so you can get an accurate measurement. Its important so we can proceed with a real plan of attach. You will also want to make a fingerboard simulator as described -- note it too has the clearance holes.

Hi Ken,
I understand what the Martin Video & your are saying about sanding the rim top flat (to avoid the hump). What concerns me is, if I do re-sand the rim flat using this method, I will in effect, make where the neck block & the sides are even shallower than it already is, as well as the waist area. I really don't want a less deep OM than what the depth is now. From my novice point of view, it seems to me that the neck block (towards the soundhole) is ramped/angled too high & pushing up on the top, causing the fingerboard top to hump. If it weren't for that, I believe I'd have a straight plane to the bridge & no gap under the fretboard extension?

Remember the top of the neck block MUST BE FLAT, using a contoured
sanding device creates a domed surface in both directions --- exactly what we want on the
back of the rim. However, doming the top of the neck block and the center of the lower bout
area is undesirable and will cause a hump under the fingerboard extension.

I set the rim in my mold & have it to where it's level in the mold. You can see where it stands proud at the waist. What you're saying is, eliminate that excess rim wood as shown? Won't this cause the bridge area to drop lower than it is now & take away some principles of the radiused top?



I watched this YT vid presented by Mike Haney where he explicitly states that a radiused top will stand the test of time. He does make some interesting points. It's quite long (1 hr) & one more thing to confuse my miniscule mind. LMK what you make of it.
http://www.youtube.com/watch?v=QjScBEDZ ... plpp_video

I set the neck on a flat board & drilled holes for the locators. Putting a square on the heel, I get 90 degrees w/ no gaps!

Yeah its all confusing -- and claims abound. Martin made (talking about vintage Martin) and are now making "flat top guitars" (52' radius on the X and tone braces) the only advantage to a dome top is that they have slightly more surface area, when they dry out from low RH they tend not crack but rather shrink and sink. The dome is not stronger in the case of a guitar that has the bridge glued to the surface -- the strings are pulling the bridge up "opposite" to natural resistance strength of an arch. On the other hand violins, cellos, jazz guitars etc. with tail pieces have the strings bowed across the bridge "pushing down" and indeed the arch is providing resistance.

I can only tell you how to do it the right way. I have no idea if your solution is going to work or make things worse? In my view that rim is really distorted on the top edge and is going to cause you grief. Where did you get that kit? If its from the Martin factory or one of the Ebay sellers the braces are flat on the bottom or 52' contour.

I've been following forums for a few years now, and I don't think I've seen even ONE post from someone building one of Ken's (KMG) kits that had a neck angle or set-up problem. His system and his parts are spot on.
My $.02
Dave

And if you want to get this right, the heel cheeks need to be 88.7 degrees to the FB plane -- the math does not lie you must pitch the neck back away from the sound board.

And with all due respect for Mr. Haney and others who prefer tight radius top bracing, note here that with all their history, experience, and technical resources Taylor chose to construct their top of the line R. Taylor Signature models with "flat tops"

http://www.rtaylorguitars.com/Woods-Bracing.aspx