Positioning a bridge ?

baldy

I have modified & refinished a Yamaha RGX 121, from H/S/H with trem bridge to H/H with a fixed bridge & am in the process of re-assembling it.
I have swapped a few bridges before but they have always gone in the original studs or used the original screw holes & this is the first time I have replaced a bridge with a completely different type that needs new holes drilled.
My question is re positioning the bridge.
The guitar is 648mm scale length so I have measured from the inside of the nut & marked where 648mm is on the body.
I have measured the travel on the saddles, which is 9mm.
I assume I want to position the bridge so that the saddles are in the middle of their range ie 4.5mm therefore giving me 4.5mm of movement either way for intonation ?
Assuming this is correct then I need to position the bridge so where the strings come off the saddles is 652.5mm from the inside of the nut ?

Bridgehouse

I usually position it in the middle of the saddles so you get plenty of intonation adjustment in both directions. This however may not be the “correct” way to do it - but it’s always worked for me

FatPete

I'd suggest going a bit further back. Correct compensation *should* mean that all the strings are longer than the scale length and 4.5mm might not be enough to get the low e dead-on.

Have a look here: https://www.stewmac.com/FretCalculator.html If you select 'acoustic guitar' it shows the compensated scale length for the top and bottom strings (rather than measurements nut to bridge screw if you select electric). For a 648 mm scale, it suggest 2.259 mm extra for the high e and 5.453 mm for the low.

ICBM

No - you need to position it so all the adjustment range is *behind* the 648mm position. Strings never intonate shorter than this and if you set it so there's equal range in both directions you will probably run out of adjustment on the lower strings.

First double-check that the scale length is 648mm, if you haven't already - don't go by manufacturer's spec, measure from the nut face to the bridge-side edge of the fret crown on the 12th fret, and double it.

If it is 648mm then I would set the top E saddle as far forward as it will go and put that at 648mm from the nut - or if you're worried, 647mm just to allow yourself a slight bit of room if the holes are not drilled exactly where you think they will be, they can 'wander' slightly in the wood.

baldy

@ICBM thanks for that advice.
It turns out the scale length is actually 650mm & not 648mm ie nut face to bridge side of 12th fret is 325mmm & not 324mm.
So I will set the saddles as far forward as they will go & mount the bridge so the saddles are 649mm from the nut face ?

ICBM

baldy said:

@ICBM thanks for that advice.
It turns out the scale length is actually 650mm & not 648mm ie nut face to bridge side of 12th fret is 325mmm & not 324mm.
So I will set the saddles as far forward as they will go & mount the bridge so the saddles are 649mm from the nut face ?

Yes, that's exactly what I would do - if that's to the bridge side of the 12th-fret *crown* and not the edge of the whole fret though - there could be almost 1mm difference there.

If you're not certain, setting them so they're 648mm from the nut should cover both possibilities and leave enough room - 7mm travel is probably enough (as Funkfingers said in the other thread I think!).

baldy

Thanks for the advice guys.
Bridge fitted & all strings intonate fine