Acoustic Guitar Construction

Regarding the distortion I see in the photo of the rim relative to the top edge of the mold -- over the length of the 22" cord of a 28' radius arch the rise at the apex (center) is only .1875" so the rim waist curves should be only "slightly" higher then the top edge of the mold.

kencierp wrote: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'm not seeing any distortion in the rim. The top fits on snug & evenly all around. I'm not challenging you. I'm just not sure what you mean. This OM body has it's share of issues that will make it somewhat less than an ideal guitar. I'm going into this, to learn from mistakes I make, but I'd still like for it to come out OK...& I know: 'You can't make a silk purse out of a sow's ear'.

The rims were from an ebay seller I don't deal w/ any more. Basically, a discarded Martin set. It was a Steve Miller 000 Martin rim set that was assembled, but w/o a back. I bought a separate figured Hog back & side set from another seller, but used only use the backs (that I joined) for the Steve Miller rims. The neck, fingerboard, & TR came from John Hall I believe. The top & braces came from Steve at Colonial Tonewoods. I joined, braced & scalloped (braces are radiused) them to the top when I first started this build. So yes, It's an asst parts kit. I was thinking it would be a good build to get savy on, since the other Martin kit I have is higher end & don't want to screw-it-up! It's almost done: I need to finish it (paint-wise), set the DT neck, & mount the bridge.

top:

Regarding the distortion I see in the photo of the rim relative to the top edge of the mold -- over the length of the 22" cord of a 28' radius arch the rise at the apex (center) is only .1875" so the rim waist curves should be only "slightly" higher then the top edge of the mold.

I dunno? If I lower the waist more than it is, wouldn't that also lower the 'bridge (apex) point" also? That in effect, would cause the previous 3/8" space at the bridge I have now, to increase measurably. Resulting in quite a steep angle. With things in place & doing a visual. I'm right on the money w/ all the measurements; neck angle & alignment, no gaps, no ramp...etc. I'm afraid that if I go messing w/ it at this stage, I'm really going have a bigger problem. With a straightedge, the neck angle gives me between 5/16" & 3/8" of space off the board in front of the bridge.

Most likely, everything will take on a whole new meaning after it's all glued together & I hear what you're saying. I'm certainly no engineer, I'm a retired house painter so a lot of the technical notes have a tendency to ride above me. I'll try to keep this going & see where it lands.

Rich

I admire your spunk, Rich!

My $.02, which makes a total of $.04 for me today, is: don't guess or hope that it works out. You can KNOW it is going to work. It's in the math, and it is repeatable, time after time.

I've not built an electric guitar, but I'm sure some of the skills carry over, if not the construction technique.

We're pulling for you!

Rich -- Ditto Dave, best of luck with your plans.

For those of you following this link I'll sum up the situation going back to the original photo of the poor fitting neck joint "high and off angle" What was determine by the measurements and other photos is that the neck heel is not angled properly, its 90 degrees and should be 88.7 +/- degrees. And also the slope of the top edge of the rim is also incorrect. With the rim clamped in the mold with the lower bout flush -- there should be a small amount revealed at the inner waist curve less than an 1/8"


and the neck block should be about 1/16" below the top of the mold. If you want to check a rim that has not been contoured with a dish you can simply set it on a bench top edge down -- it should lie flat with a small gap (.055"+/-) at the neck -- yes its that easy!!

kencierp wrote: I'll sum up the situation going back to the original photo of the poor fitting neck joint "high and off angle" What was determine by the measurements and other photos is that the neck heel is not angled properly, its 90 degrees and should be 88.7 +/- degrees. And also the slope of the top edge of the rim is also incorrect. With the rim clamped in the mold with the lower bout flush -- there should be a small amount revealed at the inner waist curve less than an 1/8".

The neck block should be about 1/16" below the top of the mold. If you want to check a rim that has not been contoured with a dish you can simply set it on a bench top edge down -- it should lie flat with a small gap (.055"+/-) at the neck -- yes its that easy!!

That's how it was: ---> I've since readjusted the heel & block & corrected the angles. I now have a straight line from nut to bridge w/ a space of 11/32" in front of the bridge...w/o any gaps & no hump! Any areas that look like gaps are only because the binding is not on & appears to look like a gap...it's tight. Remember, it's not glued-up either...only held together w/ clamps.

Ken: I've asked this twice before & still haven't got a reply? If I went ahead & flattened the rims at waist (like you're sayin'), would it not in effect, lower the bridge area well below what it is now, causing a steep neck-angle? I don't see the rim as distorted, only taller. The perimeter depth from the neck block to the tail block gradually increases proportionally. I don't see this as being problematic. Or: will the bridge stay at it's locale, being the top is radiused & stiff, maintaining it's arc & only pull the edges in to the rims when set?

I'm am not refuting you or Martin's building techniques, I have 5 of them. One thing that puzzles me though: Out of those 5, 4 of them have minimum saddle showing now, losing break angle & these were all made w/in the last 9 years. I believe the bridge/top has dropped slightly. Not enough angle was built into them from the get-go to compensate for this as they age. The 5th one is a '90 model & is the worst of all, but it is 22 years old. I like my action low, but well w/in spec (5/64"- 4.5/64"). One model in particular, an Madagascar OMC-28 LJ model (w/ warranty) & right from the start it had an issue w/ the neck angle. It's saddle is almost buried & the action at the 12th fret is at 6/64" - 5/64". What's up w/ that? Since I live right by Gryphon, I frequent the store ocassionally & know Frank Ford. I have spoken to him about about this a few times. So far: Martin declines to deal w/ it & Gryphon says: "wait till it worsens"...lol

Rich -- again I only know the expected results of the prescribed/finite formula which includes a heel angle of 88.7 degrees +/- I can see that your neck (there is a gap under the finger-board) in the newest picture is still tipped up toward the sound-board so it appears you do not have a straight line or perhaps I am not seeing what's in the picture. If I am viewing this correct, when you glue all the parts together you will have a ski jump at the 14th fret. That said, I am sorry, but I do not wish to go into a bunch of what if's and try and analyse cause and effect of your various measurement on parts and locations that are not even secured. The procedure and formula used for the KMG kits allows even first time makers to proceed in the progressive steps of the build without worries of neck fit/set or set up problems.

I agree with Ken, but at the same time if you are getting the correct gap above your bridge, go for it! There is a definite formula to follow but you can still arrive at acceptable action if you don't follow it. The problem becomes greater when you over analyze things and become paralyzed to move forward. You can still adjust the neck angle once you glue on the top just don't glue the neck on!