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CBG design confusion

My first CBG design. Here are my thinking aloud thoughts:

I was keen to have a 300 x 200 box, with the bridge about 60mm in from the rear side, allowing for plenty of vibration area on the box.

To get a 648mm (25 1/2" ) scale length, from nut to bridge, seems to be a popular scale length, I found that I would need a fretboard length of 648 -(300-60) =408mm (16 1/16") long, and allowing for a 4" headstock, the overall length of the guitar would be 300 +408 + 102=810mm (31 7/8").

Next step is to work out the fret spacing for a 408mm (16 1/16") long fretboard, and how many frets I get?. Can anyone please advise how I go about calculating these. Modestly, I am a bit good at Maths, except when it comes to Probability :)

The alternative would be to use a scale length of 610mm (24") and a fretboard of 440mm (17 5/16") long, and I found the fret spacing for that - see attached. But it would mean either shifting the bridge 38mm toward the centre of the box to give a 610mm (24") scale length, or not do the last few frets on the 24" fretboard.

So now, this is where I am at - twisted myself in logical and mathematical knots, and not quite knowing what to do.

I would appreciate some sensible suggestions on the best way out of this please

Cheers,

Jill

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Attachments:

Fret position -24 in.JPG, 66 KB

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Permalink Reply by BrianQ. on February 25, 2022 at 7:21pm

Moving the bridge towards the middle isn’t bad, it actually gives more vibration than having it towards the end? Look at a guitar, the bridge usually sits 2/3 back from the front of the body to optimize string vibration? How many frets do you have to cut out, if it’s only a few, I doubt you’ll miss them? Fretscale calculators & templates are easily found on the internet, like the Stewmac calculator or FretFind2D, which gives the option to print a physical layout rather than measurement info?

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Permalink Reply by JillB on February 25, 2022 at 9:11pm

Thanks BrianQ, you have help me decide to move the bridge towards the centre, which is not really a big problem as it will still be only 1/3 of the way from the back edge to the front edge. ( or 2/3 from the front, as you indicated acoustic guitars are)

I was unaware that the bridge should be placed where there is greater vibration, thanks for that. I really need to understand /learn the theory of guitars better.

Thanks for the info on Fretscale calculators, never knew they existed.