Hey guys - I have just completed a 20" scale CBG for my grandson and tuned it GDG - 36, 26 and 17.
1/8" Baltic Birch ply front with 2" sound hole and f slots and part of the neck is recessed off the front.
Is that the right gauge to use?? and it's not very loud. Any suggestions.
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... on the other hand, Shane Speal, in his video about using a dado blade to put a gap between the neck and the box lid, specifically leaves enough wood at the bridge so the neck will be in contact with the lid there. He makes a gap above and below the bridge but not at the bridge. His thinking presumably is that the box lid is under high stress at that point from the strings pulling down on the bridge, and he wants it to be reinforced by the neck at that point. (He doesn't say that specifically but that's what I assume is the reasoning.) Obviously, though, if leaving the lid unsupported under the bridge works for you, go for it.
As for the string gauge, ideally if you reduce the scale length by a certain factor, and want to keep the same string tension using the same type of string, then you should increase the string diameter by that same factor. For instance going from 25.5" to 20", the new scale length is 0.78 times the old, so the string diameters would be 1/0.78 = 1.28 times larger to result in the same string tension. 36, 26, and 17 would become 46, 33, and 22 ideally. But in reality (especially for a child's instrument) you might want lower tension, so not as big an increase in diameter.
Hey thanx Rich - I'm starting to think stretching the kids arms would have resulted in WAAAAY less math!!!!!
I had the same thoughts about the pressure from the bridge on unsupported areas - I'll have to try some experiments one day.
Hi , jawbone . Good move going to larger string gauges ! I did that on grandson number two build and liked it , but found the tension a bit hard to fret (it is fretted ) , tuned GDG . I don't remember the exact gauges ,though !? Ugh ! Good for slide though and a "bigger " sound . Oily and darryl are "dead on" on their soundboard advice . As you work the "effect" of the plucked string on down you get to times that "effect" by the effect of the soundboard and box. So yes , the soundboard is the biggest issue . On this current build you could try a bridge that is arched ,in the middle, on the bottom , so you have two "feet" setting on the soundboard to each side of where the neck is glued . That should help a bit . I have taken to screwing on the necks ,it reduces my glue up stress, and allows changes if needed . A screw on neck also makes it easier to mount mag pups in the guitar ,for me . I like to have a fingerboard , even on a fret less build . It helps strengthen the neck , creates a better "break" angle on the strings from tuners to nut and allows the strings to be further away from the top of the CBG . I take a 1 /16 to an 1/8 of a inch more off where the back of the neck meets the lid of the box to get some neck angle . Such a joy to make CBG's for kids ! Happy building !
Yes, I like that idea of the arched bridge!! I may let him try it the way it is just to see if he uses it as a guitar or a hockey stick, first.
others who know more will pick up on this,but it would really help if the s/board could move around the bridge i,m sure
nice looking build btw
hi jawbone i,m no font of knowledge,but as you say the bridge is sitting over a solid part of the neck,was wondering if the s/board is free to vibrate?,if not maybe an 1/8th off the top face of the neck indide the box might help,good luck
Hey Darryl - about 6" of sound board is free, the part around the 2" hole and the rest is glued.
Hi, jawbone . I have found 20" scale CBG's tuned up to AEA have a better string tension , using the same gauges as you would for a 24"-25" scale tuned to GDG . Nice looking CBG ! But,now I've got to not sound like a butt . ha! I see a couple things that are killing the sound . The bridge is stopping a lot of string vibrations from reaching the soundboard . The mass of the bridge is just too much . If its removable try a bridge that is minimal in mass , with a small footprint . Closer to what is on a arch top guitar or violin . It's all about getting that soundboard to work for you . Oh.....speaking of soundboards .........that brings me to point #2 ,where I try not to sound like a #2 . The area of sound holes has taken away to much soundboard and the box(as a sound chamber) . Nothing to be done about that ,..on this build . I'm sure there's more to come !! I've built two for grandsons and will be building two for granddaughters ! ha!ha! Happy ,building !!
Thanx Sharecropper - any and all info is very welcome - the bridge is just floating so I can change that but it is sitting over the solid part of the neck so it may not change much.
I may see what ukuleles use for strings and try that approach as well.
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