Intonation a little out of whack

[Quickstep192]

I’ve noticed that the intonation on the low E on my Martin D-42 is a little sharp.

The other strings seem OK which makes me wonder if it has anything to do with the way the saddle is intonated toward the pins. (See pic).

The strings are Martin SP 80/20 Extra Lights. I don’t recall having this issue when I had mediums on it, but I’d expect the problem to be worse with mediums.

[RRuskin]

If you want to stay with extra lights, your saddle will need to be re-intonated. But before doing that, relief and nut slot height should be checked and adjusted if needed.

[rick-slo]

Originally Posted by Quickstep192

I’ve noticed that the intonation on the low E on my Martin D-42 is a little sharp.

The other strings seem OK which makes me wonder if it has anything to do with the way the saddle is intonated toward the pins. (See pic).

The strings are Martin SP 80/20 Extra Lights. I don’t recall having this issue when I had mediums on it, but I’d expect the problem to be worse with mediums.

If anything a recessed saddle contact would make intonation a little flatter as
you fret further up the neck.

[John Arnold]

Saddle angle is a compromise. Martin chose a shallow angle which tends to exhibit slightly sharp intonation on the 6th string, even when compensated as far back toward the pins as possible.
Increasing the saddle angle will improve the sixth string intonation, but it will tend to produce flat intonation on the 4th and 5th strings.

[rick-slo]

Originally Posted by John Arnold

Saddle angle is a compromise. Martin chose a shallow angle which tends to exhibit slightly sharp intonation on the 6th string, even when compensated as far back toward the pins as possible.
Increasing the saddle angle will improve the sixth string intonation, but it will tend to produce flat intonation on the 4th and 5th strings.

deleted comments

[Quickstep193]

I’m a bit confused. When you say saddle angle, do you mean the angle of the saddle relative to the bridge, not just the way the saddle is filed? Changing the saddle angle would be not trivial task, right?

By the way when fretting my 6th string at the second fret, the intonation is out by 10 cents.

Also, I would have thought lighter strings would be less affected than heavier strings. Is that correct?

[keith.rogers]

Originally Posted by Quickstep193

....
By the way when fretting my 6th string at the second fret, the intonation is out by 10 cents.
....

Changing the angle of the saddle is probably going to require a new bridge if you want to make the overall length of the 6th string longer, especially on a bridge with the pins straight across (as in OP's picture) vs. Martin's newer bridge with the pin angle more closely following the saddle's.

I'm not sure what 2nd fret intonation means here, but the nut height has a lot of influence on intonation in the lower frets.

[JLS]

Either a bad string, or an unset witness point.

[rick-slo]

Originally Posted by Quickstep193

I’m a bit confused. When you say saddle angle, do you mean the angle of the saddle relative to the bridge, not just the way the saddle is filed? Changing the saddle angle would be not trivial task, right?

By the way when fretting my 6th string at the second fret, the intonation is out by 10 cents.

Also, I would have thought lighter strings would be less affected than heavier strings. Is that correct?

You can shape the saddle to have one break angle from the pin to the far edge of the saddle where the string leaves it. However often there is some curve which IMO is better. General idea in photo below:

[redir]

It does appear to me that the saddle is carved forward on the 6th string and you could move the contact point to the back edge. That would at least help a little.

[Quickstep193]

Originally Posted by redir

It does appear to me that the saddle is carved forward on the 6th string and you could move the contact point to the back edge. That would at least help a little.

It’s actually carved back (toward the pins)

[redir]

Originally Posted by Quickstep193

It’s actually carved back (toward the pins)

Ok well that's that then. If it really does drive ya crazy you could have the slot widened. But first, how is the action at the nut? The nut slot should be the same height as the fret in front of it, if not that can cause intonation issues too.

[Howard Klepper]

First, get relief and the nut slots optimized. Then put on a fresh set of strings.

If the intonation on the bass E is still sharp enough to bother you, you or a tech can take a short piece of bone saddle, appropriately size and shape it (you will probably want the string to leave it right at its forward edge), and put it behind the existing saddle for that string only. Let it sit on top of the bridge, and glue it to the existing saddle with one tiny drop of CA glue.

[cliff_the_stiff]

Originally Posted by John Arnold

Saddle angle is a compromise. Martin chose a shallow angle which tends to exhibit slightly sharp intonation on the 6th string, even when compensated as far back toward the pins as possible.
Increasing the saddle angle will improve the sixth string intonation, but it will tend to produce flat intonation on the 4th and 5th strings.

This has been my observation as well.
I compensate the tuning flat a little.
(I place my finger on the 3rd fret and tune it to G to match the g string)