This crudely-drawn picture describes the 2 techniques I've come across here at CBN and at various places around the interwebs. In both cases, a wood rail is glued either directly to the neck, or on the opposite side of the cigar box wall. A bolt can then be plunged through the rail, ending in the neck:
The top drawing has been modified by a few people so that the rail runs parallel underneath the neck, not perpendicular, across the length of the box.
I bring this up because I want to open things up for discussion: additional examples, comments, criticisms of the technique, etc. Please feel free to comment, especially if you've tried any of these techniques.
Replies
Ted Kaczynski said:
ChickenboneJohn said:
It's not so much the length of the neck as the tension on it, so high tunings and heavy strings exert higher forces. If you think about how much rigidity a neck thru' construction gives you, and how stiff the neckstick is, I'm shooting for a similar sort of strength, hence a decent overlap between end of the neck and the heel block or thru' block. Wider spacing on the fixings gives more strength/less stress on the joint fixings, but 2" spacing works well.
Scotty C. said:
John, I see that your picture says approximately 2 and a half inches, which answers my first question. Does a longer neck mean longer bearing space?
Yes, I'm also rethinking my plans. In your drawing (neckjoint.jpg), you show a 2.5" overlap between the neck and the underlying support beam that spans the length of the cigar box. I only had a 1.0" overlap. So, to extend mine to have a 2.5" overlap, I'd have to move the neck down into the box another 1.5", which is feasible, but it would require that I move the bridge back another 1.5" to maintain the scale length. This means the bridge would move from 6" down a 9" long box to 7.5" (or from 66% down to 83% down the box (toward the tail piece)). I'm worried that if I do this the box won't resonate as well. I heard (read) that the bridge should be about 2/3s down the box. So, at this point I remain undecided about which way to go. As it is now, it sounds good and I enjoy playing it. Maybe I'll opt just to redo the heel so as to maintain the current sound.
My next head/neck assembly is already in process, and it is a laminate composed of 3 strips of wood that's 2" wide by 0.25" thick. I'm not sure what kind of wood it is, but it pretty and it seems fairly hard. Since I glued it up, the laminated neck is really rigid and is long enough to do a thru-neck. My problem in China is finding a source of good quality wood for building head/neck assemblies. I got this wood at B&Q, but they don't sell the 1.5" x 0.75" hard wood that you can get easily in the States from Lowe's or Home Depot. The other wood I got from a Chinese source was not kiln dried (wood is sappy). Anyways, if this new neck works out, I'll probably be doing a lot more laminated necks. With a 2" wide neck I'm thinking maybe a six stringer tuned DD-AA-dd or GG-DD-gg or maybe a 8 stringer long neck diatonic mandolin. Hmmm... Let me think about that some more...
Thanks for your suggestions.
-Rand
ChickenboneJohn said:
If the existing neck only projects a little into the box (about an inch or so?) as per your drawing, you'd have to make a new longer neck or slide the existing one in maybe an inch or more to increase the bearing where you are screwing into the bigger internal block. This will shorten the scale length (a problem if you've fretted it or marked the frets), or you'll have to shift the bridge position back by a corresponding amount. Both of these may have some effect on the sound, so it will be nigh-on impossible to gauge what's changing the sound.
Once you start tinkering with two things at once. (ie putting a bigger heel block in AND moving the bridge or shortening the scale) it's hard to know what it really having an effect. To really assess what difference a change makes, you need to do one thing at a time. It's just being methodical..but that doesn't suit everyone, and quite often a bit of serendipity and luck works best!
Good luck
Thanks for the feedback. I'll use your suggestions to retro-fit my CBG and remove my "tacky" heel. I guess I am too worried about the acoustic effects of filling the cigar box with a of extra wood framework, etc. So, this build can be my testbed to see if adding additional wood (reducing internal empty space of the resonator) actually has a negative effect (or not). I've been playing all week with my new CBG, and it sounds pretty good, but looks a bit ugly with my quick and dirty heel. I'll see how it plays when more internal support is added. Thanks again.
-Rand.
ChickenboneJohn said:
See how far apart the screws /bolts on a Fender style neck are spaced - about 2 inches? They've done the hard work for you - it works. Space your fixings like this (2 are fine for a 3 or 4 string) and put a corresponding block under the end of the neck to fix thu' and it will be good. You don't need to weld bolts to the neck reinforcement or add a heel...keep it simple, don't make it hard on yourself.
Rand - the reason you needed to add a heel was that the fixing block simply doesn't project into the box enough and couldn't resist the twisting moment (engineering term for a force that's trying to turn something) exerted by the strings - by the way, that internal backing board is adding no significant strength to the joint. A bit more solid timber blocking inside the box isn't going to hurt the sound as long as you keep it away from the vibrating top, and guitars always work better when they don't fold in half when strung up.
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