Bridge replacement and intonation
 

Ok, doing my first bridge replacement on a cheap acoustic and would like confirmation that I understand the basics of intonation. This much I understand…the saddle needs to end up at the same distance from the 12th fret as the distance from the nut to the 12th fret. Now what about the saddle being a few degrees off-square from the strings so that the low E vibrating length is slightly longer than the corresponding length of the high E, which I have noticed in several low to medium priced guitars - -is that a cheap way to improve the intonation? I measured a Godin I have and found that the distance from the 12th fret to the saddle was 1/8” longer for the low E than the high E, with the high E being at exactly one half the scale length. The guitar I am working on had a saddle square to the strings… so will a slanted saddle necessarily give me better intonation? In other words, does a slanted saddle always improve the intonation over a squarely placed saddle? Thanks.

You can stop there.

I've dedicated about 20 pages or so to an introduction to the subject of guitar intonation as part of my Basic Guitar Setup101. It can be found here: http://charlestauber.com/luthier/Resources.html

I'm not going to attempt to condense that to a few paragraphs here.

For SS, the answer is yes, a slanted saddle will intonate better. Typically, the high e needs about 1/16" compensation and the low E about 3/16".

For nylon strings, compensation is much less, and a straight saddle is frequently used.

Thanks Charles and Roger. With all of that information, I should be able to get close enough for a $65 eBay fixer upper. Charles, I am a mechanical engineer, but your dissertation on the subject is going to take me a few readings to fully grasp; for this project I will go with the 3 and 5 mm approximation.

The distance between the nut and the 12th fret is half the 'theoretical' string length. It is theoretical because when you press a string down you tighten it and therefore raise the pitch. You add to the theoretical string length a small amount in order to 'compensate' for that raise in pitch. The idea is that the bit you add on lowers the pitch by the amount the pressing down raises it and you end up in tune.

The amount added varies depending on what kind of string, what gauge of string and how high the action is. StewMac sell a very nice tool (nice but not necesary) that helps you set bridge saddles.

http://www.stewmac.com/freeinfo/Repa...ed/i-4462.html

Although you don't need to buy the tool the page gives information on compensation that I found useful when setting a new bridge on my guitar. I made my own tool out of four pieces of scrap 1/4" square offcut and have used it again since.

L'Arrive guitar's at 650mm scale have the high E saddle compensation set 1mm back, and the low E 3mm back last time I measured. The rest is done by individual string compensation either by creating 2 slanted peaks in the saddle top or by dropping in a moulded plastic compensated saddle.

Different manufactures at different times used different degrees of slant, to varying degrees of success. 1-3mm should be fine.

Even an incorrectly slanted saddle slot will usually give better intonation than a straight one, provided the slant isn't too extreme.

I use 0.075" (5/64") for compensation at the first string, measured to the front edge of the saddle. I generally use a 2 or 3 degree saddle angle. Most of my saddles are 0.095" to 0.100" thick. Compensation is on the front edge on the first, third, and fourth strings, the back edge on the second and sixth, and the middle on the fifth.

Awesome, thanks for posting this.

You're welcome.

The version of the document originally referenced below is the unabridged version that includes a longer, more detailed discussion of intonation: http://charlestauber.com/luthier/Res...1-Sept2018.pdf

Ned, please talk in terms of thousandths of an inch rather than millimeters when discussing compensation (and action heights as well for that matter).

Thank you in advance.

You got a problem with Standard International Units? :wink:

Lots of Classical makers use metric by preference, and even some of us who make steel strings do. I do, however, appreciate it when people avoid fractional inches.......:) What in heck is 41/128"?

Ned, I appreciate the metric measurements, means I don’t have to convert it in my head when reading.

Steve

8.136 mm, or 0.00004044 furlongs