Bridge placement math

I run the G string saddle all the way forward, then run it back one or two full.screw turns, then set the center of the G string saddle exactly 2x distance from nut to 12th fret. In practice you are very unlikely to need to move the G string saddle forward to intonate. Somebody may have a more precise methodology, but thats worked for so me so far.

 

So, for an example, I'll use my current bass- 34" scale.
If the G saddle is all the way forward and set at 34"/ 17" from the 12th fret,..
does that mean that the lower strings typically require a distance longer than 17" from the 12th fret to intonate properly?
It seems like the G saddle is always the closest.

 

Today is Bruce quoting day methinks

SoloRail bridge placement /multiscale query.

 

That also answers my question.
If the nut and 12th fret are fixed and the G is pretty much right on, then the fatter the strings, the longer the second half is after the 12th.
I wonder how much this changes with lower tension strings, or strings that are closely matched in tension.
I guess I'll find out when I set mine up.

 

Looking at Bruces numbers for the G string, he says .060", which is close to 1/16th. How far back a couple turns will get you on the saddle may vary depending on the screw pitch, maybe safer to call it 1/16"? Thats about what two full turns gets you on a Ric bridge anyway.

 

I think Bruce’s math is valid. I was always told a rough rule of thumb is to add the thickness of the string to the scale length and you’ll be pretty close.

 

That's what my experience has shown too. If you set the saddles at 50% of the way back you'll get very limited ability to intonate. I put the G (or C) saddle all the way forward and crank it back just a smidge and then align that with the scale length measurement. The rest will fall into line when you go to set up and intonate. Where Bruce's numbers are really handy (IMHO) is when you're doing a multi-scale.

 

I believe that is a false claim, for any normal string set. Have verified my belief with a few tension references.

 

I'm with you, I've always worked on pretty much the same logic, for bass or guitar. (though for guitar I don't back of the top E quite as much, less overall travel to work with on guitar bridges)

 

I'm going to lurk around this post because I will soon do a bridge install myself (first timer).

 

Just thought this was worth mentioning. If a new or replacement bridge is a traditional Fender style, bent plate bridge, with five screw mounting, then placing them all (and this includes many copies such as Gotoh standard, Gotoh GT201, Wilkinson, Hipshot Fender copy and several others) can be done using a measurement of 35 inches, from the fretboard side of the nut and making the 35 inch mark the distance for the bridge mounting screw holes. Virtually all those Fender style bridges are the same dimensions and have almost identical length screws for saddle adjustment.

Images, Fender dimensions, Gotoh dimensions, Hipshot Fender replacement, Fender standard, Gotoh standard Fender replacement.

 

it isn't this. It is about compensating for the deflection of the string when fretting.

In an ideal world, the fret would move to the string and the string would stay straight. Under these conditions the bridge saddles would all be in a line and the 12th fret would also be at the half-way mark.

In the real world, fretting a note requires deflection of the string to push in into contact with the fret. This deflection adds tension to the string which increases the pitch. The amount of by which the pitch increases depends on the gauge of the string. Actually is it the mass per metre that matters, but generally speaking a thicker string will have more mass per metre than a thinner string.

As the mass per metre goes up, the pitch change for a given deflection also goes up. Prove this by bending a G string 1/4 of an inch and comparing the bent pitch with a similar bend on the E string. Moving the saddle back lengthens the speaking length which flattens the pitch in opposition to the sharpening effect of fretting a note. It is not a perfect solution but can get pretty close. Better is to lower the action and flatten the relief so as to minimise the deflection. Note that bridge adjustment cannot compensate for a poorly cut nut and the related intonation problems in and around the first few frets.

 

Great detailed, but easily understood explanation Steve and a clear example of what you're saying is a pedal steel guitar. As the strings aren't pressed down, all strings are the same length and the slide acts as a moving fret. No string defection so regardless of string thickness, they're all the same length.