Thinking Outside the Box (Tips, Tricks and Hints) - Question from a Fellow CBG Builder : How to Mount a Bridge Without Losing that Hollow Goodness
A fellow builder wrote in with a question that I thought other builders might also have...
"Hey! I'm making an acoustic 6 string CBG and I stumbled on your page. I was hoping you could help me figure some things out. I see you use electric bolt on necks which is what Im doing since I don't have the means to fabricate my own thru-body neck and 6string thru-bodies are impossible to find. How do you attach your necks to your bodies? I went to home depot and got them to cut a 2x4 into a bunch of pieces so I can bolt (screw) the neck on top one of those and essentially turn it into a thru body extension, will that be strong enough? I was also going for a trapeze tailpiece and bridge setup since I figured I couldn't put any load on the box lid. I see you've attached several load bearing bridges to lids tho, I was wondering how you did that and if thats possible on an acoustic setup? I figure you'd just mount it to the thru-neck thru the lid but with mounting the neck on top the thru part would sit like 1/2 inch below the lid, someone also told me that if the thru body neck is resting against the top lid it will lose its resonance anyway. Clearly idk what I'm doing 😂 any help would be greatly appreciated 🍻 Apologies, I'm still learning Ive been calling the bridge and the saddle the same thing."
Definitely something I myself tried to come up with a few different methods for, but I've found a way that works exceedingly well and seems to compliment this style of instrument, regardless of whether one is going for an "acoustic-y" build or an electric one. Here is what I sent as an answer to his question:
So, first of all, congrats on being a fellow "outside the box" thinker (pun). You definitely have to mind a few things when mounting necks and bridges on these types of instruments. You also have to choose your boxes wisely, and remember that the simpler your build can be, the more options you will have for boxes. I have to choose specific boxes for the more complex configurations, BUT I can say a few things remain the same. Let me try to explain, and see if I can find a couple reference photos to help demonstrate.
You are correct that if everything is in contact with the lid (which is meant to act as a primitive sound board), it will dull the resonance some. All but 2 or 3 of my builds feature lots of space under the lid. Some more than others. And only those 2 or 3 have full-contact between the lid and the center-plank (usually due to an abnormally-thick plank or -thin box). With CBG's intended to be primarily "electric", I worry less about getting the more hollow sound, and I focus on making them stout, solid-feeling and less prone to feedback, so they have more of a "chambered electric" thing going on. The key there is to begin the construction in a manner that mimics how a typical electric guitar is built, and then leave yourself room to pivot.
I use 1x3's or 1x4's mostly for this reason (and the occasional 1x6), because they're kind of close to the thickness of the wood a neck attaches to in a typical bolt-on neck guitar (actual thickness on a "1-by" being about 3/4" and all). I've ended up using the occasional full-inch-thick planks, but have had to plane/route down the neck mounting area or find some screws that can accommodate the extra thickness. Or in a couple cases where I was hiding the neck joint, I used some of the "flush-mount" neck screw countersunk grommet things to knock a 1/4" or so off and have the standard neck-mounting screws end up being flush with the bottom of the wood. Either way, the end result allows for space between the majority of the center-plank and the lid in most cases, to keep some of that natural resonance.
With your box, it's always a good idea to use an off-the-shelf electric guitar to help determine how deep to make your "slot" for your neck. Some boxes that are approximately 1 & 3/4" or less, you can cut your neck slot all the way to the rear/bottom and just leave the box bottom as your "zero point", with the entire center-plank lying against it (and I recommend anchoring it to the back, whether it sits flat against it or if you have to build a couple little "risers"). The goal here is to have the end of your fretboard about the same height off the guitar's top surface that it would be on a standard electric guitar (dependent, obviously, on what kind of bridge you're using and whatnot). If a box is 1 & 3/4" or less, for example, you're going to want to have that center-plank lying against the inside bottom of the box to get the best possible action. With a deeper box, you'll use the depth of your plank plus the depth of the neck itself to give yourself a rough idea how far down to cut to put that fretboard at the right height. Then you just add a couple of "risers" underneath to get that center-plank reasonably level with the neck slot bottom.
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| Here is a picture of an Avo box where I had to add a little height support the center-plank at the neck and the butt-end of the guitar. On most builds, I run a finishing screw through to the center-plank at those points just to keep everything from moving around. |
Now let's address supporting the pressure of the bridge without killing the top's natural resonance. Think about a 335-style semi-hollow electric. While there's a lot of empty space under there, the tune-o-matic and tailpiece (especially when they have a stoptail, Bigsby or Maestro vibrola) also have to have support and solid mounting points, so there ARE a couple places where the top meets the block. So all you need to do there is create a point that either provides a solid spot for your bridge to rest on or gives you something to hard-mount your electric style bridge onto. And while it can be trial and error finding the perfect thicknesses, it's otherwise quite simple. Just remember that your goal is simply to "sandwich" some wood in there to make those points of the center-plank and lid meet the same joining piece. Often I'll use leftover scraps from other cigar box builds, my stepkid's Taekwondo breaking boards or just buy some random thin pieces or veneer from the home improvement store.
You just need to mark your center-plank where you want the strip (if it's just a floating style bridge where you're just needing support), or a rectangle just a little wider than the bridge you need to anchor down, and you'll just use the trusty Titebond wood glue to affix that to the center-plank (clamp it at least overnight), and you'll leave the rest of the space under there open. Here are some examples:
And now, and example where I used a separate bridge and tailpiece:
So with an "acoustic" setup (I don't know what bridge you're using, but Grover makes some cool ebonized-wood-bottom floating bridges that work spectacularly with CBGs) where you're anchoring a tailpiece to your center-plank, You can just simply make a half-inch or 3/4-inch wide support strip to go where your bridge will be that will support the lid to the center-plank just in that point (and again, an additional lid-support next to the neck might not be a bad idea) but you can leave the entire rest of the space empty.
Reiterating that my only other suggestion would be to switch to "1x" instead of "2x" lumber, because it will make building much easier, allow for more openness under the lid, and better approximates the tried-and-true construction of a contemporary electric guitar. You'll find certain boxes work better for specific configurations, and always have a contingency in place in case you run into an issue, because one thing I've found is that 9 out of 10 times, you can pivot on CBG building as you go and still come out with a cool finished product.
I hope this answers your questions and gives you some ideas how to make your build work the way you want it to. Any of you guys, please let me know if you have any other questions. Now get back to work!
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