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Adjustable bridge - attach to box top or through neck?

Hi, I've been lurking here for a while and have a question I just can't find an answer for - I'm hoping someone can help please.

I've gathered up all the bits for a three string CBG - I've a 8x6x2 box, some nice sapelle for the neck and a rosewood finger board, tuners, etc etc. 25.5 inch scale length. I plan to build an almost-through neck, butted up to the end of the box and bolted through. Although I am using a lipstick pickup on a slant, I'd still like the git to have some acoustic ability, so want to allow the top to vibrate as much as possible.

To do that I plan to leave a gap of about 3mm between the through-body bit of the neck and the box top. I reckon that should allow me to build in some neck relief and get a nice string break too. I'm thinking of building a slight paddle-shape into the part of the neck passing through the box, mounting the pickup in there and cutting a hole in the top around it so that the top can still vibrate. The wood I have is wide enough so it can still be all one piece.

I've found some cool conical brass tips from roller ball pens to use as string ferrules - they were being given away at a trade show :o) I'm going to put these through 6mm holes in the bottom of the box, into tapered holes in the neck piece and out through small holes in the top. Again, my thinking (based on ideas I've picked up from you all on this website) is to keep the top of the box free to vibrate but firmly anchor the strings to the butt end of the neck and stop them cutting into the wood.

This leaves me with a question though - should I attach the bridge just to the box top, or into the neck through holes in the top? As I'd like to be able to play both slide and fingerpicking styles, I've made an adjustable bridge from three bolts in an H shape. I was planning on making two holes in the box top for the bridge uprights, and screwing them into captive pronged nuts hammered into the through neck.

But then I though.... surely something has to be touching the top?

I know there are no rules but I figured I'd ask for your thoughts before I start cutting stuff up! Any thoughts you folks might have would be appreciated and apologies if this question is (a) dumb and/or (b) answered somewhere else.

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Permalink Reply by Jim Woods on July 11, 2012 at 8:25am

Yep, Since you want to have some acoustic ability, I think placing the bridge on the box top would give you the best results. A single screw / bolt should suffice, maybe putting it on a piece of wood to raise the action to desired level. But as you noticed - there are no rules, so try what tickles you.

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Permalink Reply by Bluesheart on July 11, 2012 at 11:16am

Yep, I agree with what Jim says, mount the bridge on the box so it can vibrate the top.

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Permalink Reply by Andy Eight Spades CBG on July 11, 2012 at 11:51am

Get a thin strip of wood, put the captive pronged nuts into that, and glue it to the underside of the box top under bridge area, use a nut and washer on the top side of the lid and bolt to secure it when it is done being adjusted. You might have to cut some out of the neck to give room but should work.

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Permalink Reply by Nobby 1974 on July 11, 2012 at 10:18pm

Hey guys, thanks for the input. I might pass up the adjustable bridge I've made for now and just try a single bolt on its own for starters, see how that goes. I like Andy's idea too and should have space inside to do it (if not, a rasp will make some!) so I might try that later. I'm already planning my second CBG by the looks of things... eek.

Cutting starts tomorrow...

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Permalink Reply by Mark Bliss on July 12, 2012 at 6:05am

String vibration is transferred into top via bridge, top moves air and creates soundwaves. Definitly bridge on top, not neck.

For acoustic purposes I am a fan of keeping the bridges mass reasonably low, so big heavy structures are something I avoid for this application.

Unless you are a pretty good player, dual purpose (fingerstyle/slide) design is treacherous. The only success I have really had is a design where you slacken the strings and insert a spacer/riser or different nut, that can work fairly well. But the other half of the equation that makes slide work well is a pretty large step up in string guage, which makes fingerstyle pretty tough. I suggest two guitars. Sounds like your headed there anyway.......

Have fun!

Mark

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Permalink Reply by RTZGUITARS on July 12, 2012 at 8:18am

I have not built one yet (but i will) I have used Archtop bridges on my guitars no mounting needed, sand flat ready to go. If you bulid one you can add a pickup rod. In the time it takes to retune to open G or open D you can raise the action for slide, and you can adjust intonation for any reason string size whatever. This works great on buttend tailpiece or small clamshell. I have a close up pic of one on my page. Shouldn't be to tuff to shape one.

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Permalink Reply by Mark Bliss on July 13, 2012 at 5:20am

That could be a great option, and that has one of the better looking intonation correction shapes I have seen. Many of the similar but smaller mando bridges have just got the wrong shape on the top and would need some modification.

They arent too hard to make, but time consuming. I have seen a few sources priced too low to bother making one.

One thing though, they are fairly tall, and would require some design considerations like a fretboard that is fairly high above the instrument top, and/or some neck set angle.

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Permalink Reply by Nobby 1974 on July 15, 2012 at 11:17pm

Thanks Mark. I was using a largish M10 bolt, it wasn't sounding too good and I suspect it was too heavy so I ground it in half to cut the weight but keep the look and it has more life to it now. Sustains for ages too. Thanks for the pointer to mount it on the top and not the neck - rather dumbly I was worried it would squash the box - I can see that if I'd mounted it through the top I'd have had almost no acoustic quality to it at all.

Ritz, I really like the look of that bridge and have a chunk of sapele and some indian rosewood left over, so might have a crack at making one for CGB #2 (and there will be a number two...)

It's a surprise gift for my father-in-law and he's a 60 something gigging musician and slide-head (he's got a couple of rezos, lap steel and a hofner arch top which he all plays slide) and I wanted to make him something a little different - sapele neck, Punch box, rosewood finger board and nut, brass tail piece and tele electrics. It sounds cool plugged in - very clean and warm, and it's got a nice jangly vibe unplugged, although it isn't that loud. I'm quite pleased with my first attempt. the branding on the headstock is his initials.

BTW, someone else on here suggested sapele for necks. It's mahogony-ish, nice even grain and I think a good tone wood too (warm sounding). It's also easy to work and get a nice finish. B & Q sell 1100mm lengths 41mm x41mm (so almost perfect width) for about £6 a go. I recommend it from my vast experience... :o)

CBG #2 will be mine though!