Martin Style 00 12 fret guitar now with strings!

[johnnparchem]

Sorry about the number of posts, but I am on vacation doing what I like best. I am moving along. I braced the back and have marked out the rebates on the rims. I could probably have routed out the rebates for the braces tonight, but I had a glass of wine at dinner and I hate to use power tools after any drinking.

As you can see I moved away from using a pencil to mark cuts and have switched to a scalpel for greater accuracy. The are so much sharper than an exacto knife; one needs to be careful. The mark I made on the center strip cut all of the way through the strip. After I removed the back I just chiseled the overlap off.

After working on the harp ukulele for 6 months this 00 seems ridiculously huge. I keep checking to make sure I am not using my dread patterns and molds.

[darren]

Looking good John, wish I could move this fast. :)

I have a few Martin 2-way rods that i was going to use in between some CF. The issue is that the martin adjusting section is wider than the rest of the .25" shaft. In your experience would it be preferable to route outer channels for the CF or to stop the CR short at the adjuster, in the same channel.

...sorry about the thread hijack and I can move this to a new thread if you like.

[Darryl Young]

I was curios how much stiffness CF added when installed at that location. It sounds like it does add some stiffness.

To address your question, if you take a beam and bend it, along the outside of the bend the beam is in tension. Along the inside of the bend, the beam is in compression. The tension/compression on the beam decreases as you near the centerline of the beam and along the centerline, there is no load meaning neither compression nor tension. Its called the neutral axis best I recall. So since there is no load on the neutral axis, adding additional strength to the neutral axis doesn't add any stiffness to resist bending. The most efficient way to add stiffness is to add it as far away from the neutral axis as possible (along the outside of the beam). That's why an I-beam has a narrow web through the middle (neutral axis) and 2 hunks of steel on the ends of the web, as far from the neutral axis as possible, to resist bending.

So apply this to a neck. Its made up of two different woods, often a medium density wood like mahogany, and a dense wood for the fingerboard like ebony or rosewood. Look how the strings pull on the neck and which way the neck tends to bend you see the fingerboard is in compression and the back of the neck is in tension. If the fingerboard is denser/stiffer than the neck material, the neutral axis won't be in the middle, it will move a little toward the denser/stiffer material. So in general, I would guess the neutral axis on most necks is right under the fingerboard somewhere near the glue line(varies neck to neck, but not much I would guess). So adding stiffness right under the fingerboard along the neutral axis is not efficient. The CF on the neutral axis doesn't add to stiffness at all. Ideally, the CF would be on top of the fingerboard or or on back of the neck......but that isn't practical. So placing CF as deep as possible in the neck is beneficial.........like on bottom of the truss rod channel. Go as deep as you dare without having the CF show on back of the neck. Of course the truss rod must overcome this added stiffness to make adjustments.

Looking good John!

I'm curious about the location of the carbon fiber. I would guess that once the fretboard is installed, the CF is positioned very near the neutral axis of the neck. So does it have much affect on resisting the bow created by string tension?

It sure is a lot harder to bow the neck with the carbon fiber than the wood it replaced. I can feel it when I use the truss rod. Are you saying that spacing them out further would increase the stiffness of the neck? Or setting them deeper? Or do you think they are a waste of effort. They are cool though!

[johnnparchem]

Looking good John, wish I could move this fast. :)

I have a few Martin 2-way rods that i was going to use in between some CF. The issue is that the martin adjusting section is wider than the rest of the .25" shaft. In your experience would it be preferable to route outer channels for the CF or to stop the CR short at the adjuster, in the same channel.

...sorry about the thread hijack and I can move this to a new thread if you like.

No problem hijacking my thread for me the whole purpose is raising discussion...

Now I understand why people route three channels. I think your solution would work but I have not tried it. There has been a thread in the OLF alluded to in Darryl's post above that the CF rods do not do all of the much. Maybe make the neck about 10% stiffer. I do like the rods close to the center as it is the widest part of the neck. I have read many blog posts where someone carved right into the CF rod while shaping the neck.

[darren]

Now I understand why people route three channels. I think your solution would work but I have not tried it. There has been a thread in the OLF alluded to in Darryl's post above that the CF rods do not do all of the much. Maybe make the neck about 10% stiffer. I do like the rods close to the center as it is the widest part of the neck. I have read many blog posts where someone carved right into the CF rod while shaping the neck.

I know both options will work I'm just not sure what is best... I'd prefer to have it in the center (deepest) part of the neck where you place it but I think the gaps where the CF ends at both sides of the adjustment end would bug me to no end.

10% stiffer is 10% stiffer. Its relatively cheap and easy to do. what's not to like...

[Darryl Young]

I haven't used CF so I don't know how hard it is to shape/cut but it's likely tough. On the 00 I'm making, I used a single, black line along the center of the neck (3 piece neck). I've wondered how difficult it would be to use CF as the middle neck layer and it show as a thin black line on back of the neck? That would position some of the CF as far from the neutral axis as possible so it adds the most stiffness. Just not sure how difficult it would be to profile the back of the neck.

[johnnparchem]

I haven't used CF so I don't know how hard it is to shape/cut but it's likely tough. On the 00 I'm making, I used a single, black line along the center of the neck (3 piece neck). I've wondered how difficult it would be to use CF as the middle neck layer and it show as a thin black line on back of the neck? That would position some of the CF as far from the neutral axis as possible so it adds the most stiffness. Just not sure how difficult it would be to profile the back of the neck.

Notice the hack saw I am using. It reeks havoc on any edged tool.

[johnnparchem]

On to the top! I roughed out all of the braces. I cut them close on the band saw and either plane them or use the drum sander to take them to the correct width. I am changing the bracing pattern slightly from the plans for the 00 that I have. Those plans have two 1/4" wide upper transverse braces. Having two tall braces seemed like a pain with a bolt on neck and the truss rod adjustments. So I switched to one slightly thicker transverse braces moved lower toward the sound hole a bit and a popsicle brace. This is more like the 0 sized and the D14 sized guitars I have built.



I have a few pictures of making the x-brace. This had been hit or miss for me. Now I use an angle tool to mark out the lines I want to cut. I place the braces together in my parrot vise so that only the depth I want cut is above the vise head. After cutting nice but angled lines going down, I take the time to use a square to make sure I am cutting square. Otherwise the braces are tilted.

Now I am just waiting for the braces and the maple bridge patch to set.

[johnnparchem]

My shop is taking a beating, even though I try and keep it clean. As you can see I am gluing the upper transverse brace in the 28" radius dish. I went back and forth between gluing it flat or in a dish. The brace itself has a 3" flat area in the center; the rest has the radius. In the photo you can see in the center I am using one of my honking big stewmac gobars to make sure the flat area gets glued. I was able to see by the squeeze out that this clamp did the trick. I will see how it works. Given that I am pressing it in a dish there my be a slight radius still in the center, but it will sand flat on the top.

[Darryl Young]

Looking good John!

I just went to the OLF and found the thread you mentioned. After reading it, I decided to thin the AB fretboard on my 00. Took it from just shy of 0.250" down to 0.220". I'll give that a try. If I like it, I may try the 0.200" Mario mentions on the next build. I like the idea of a lighter weight neck anyhow. I also agree with the discussion over there that ebony (or at least ebony available today) is not very stable and contributes to a lot of neck movement issues. I prefer to use a rosewood for fretboards (and prefer quartersawn no matter the wood choice). Using african blackwood (AB) on this build and I have another AB blank on-hand for the next build. I would like to try Bois de Rose (sp?) as I hear it darkens to almost perfectly black over time.......but I've never found any for sale.