Couple of strings going out of tune regularly. Machine heads?

[derp]

One of my A and D strings seem to regularly go out of tune now (started ~6 months ago). I have a Phil Davidson flat top mandolin I bought ~10 years ago. I’ve never really performed any maintenance apart from string replacements.

I live in country Australia and don’t have access to a nearby luthier otherwise I’d just pop it into them. I thought perhaps a couple of the machine heads may be starting to wear out but am unsure. This might explain why it is only a couple of the strings and not all of them. Is this a common problem?

Cheers,
Derp

[dhergert]

It's possible, but pretty unusual for turners to fail like this. Here are some other things to look at -- sorry if these are things you've already considered...

Might want to check your nut, your bridge and your tailpiece to make sure there isn't something binding with the strings as you tune them. Nut and bridge string slots in particular can become tight with gunk over time.

This may already be your practice, but tuning up -- meaning tuning flat first and then tuning up to the proper note -- tends to lock the strings into tuning best.

At the tailpiece, string loop windings can begin to loosen and/or unravel, allowing strings to slip and go flat.

Although many of us prefer older strings, the age of your strings -- and in particular how clean they are as they pass over the nut and bridge can make a difference.

Humidity extremes can cause tuning changes too. Not sure if your location is prone to these. As humidity goes low, the top can shrink enough to lower your action and make the strings go flat. As humidity goes up, the top can absorb moisture, expanding, and raising your action and making stings go sharp. Severe shifts between humidity extremes can cause body cracks.

Lastly, and this is pretty rare, but neck heel - to - body joints can begin to give way, allowing strings to go flat and action to go higher than normal; if this were your situation though, I'd expect all of your strings to be slowly going flat, and at the same time your action to be getting uncomfortable, and you'd probably see cracks in the finish around the heel/body joint area.

Good luck with this!

[peter.coombe]

There is always Australia Post. I also live in country Australia and get mandolins posted to me regularly.

[EdHanrahan]

... string loop windings can begin to loosen and/or unravel, allowing strings to slip and go flat.

HA! So rare that we tend to forget it. The ONLY time it happened to me, it was both E-strings at once ... go figure!

To Don's list, I'd add checking the screws for tuning cog and end knob. Depending on tuner design, their requirements vary (too loose is always bad, too snug may inhibit motion), and most (maybe not all) open-back tuner's knob screws serve ONLY to hold the knob on the shaft, while on many closed-back tuners, that screw also affects gear backlash & tightness. But we non-professionals can't be sure until we try.

And non-liberal lubrication is never a bad thing: http://www.lutherie.net/tuner.maintenance.html

[ProfChris]

One more possibility - too many windings of string round the tuner post. If your windings get close to overlapping previous windings, they can move around and change the tuning.

Has this happened over several string changes? If so, probably not the loop windings. In order, I'd try:

Check for overlapping windings

Clean out slots in nut and bridge, add a little graphite (pencil lead) for lubrication

Tune up to the note

If these don't fix it, then check for neck joint movement and loose tuner screws

If all that fails, it might be defective tuners, but that's really rare. Snap a pic of the button and post hole position when in tune, and compare when it goes out of tune.

And finally, bear in mind that the more lightly built and thus responsive, the more humidity changes will affect it. I dont expect not to have to retune regularly except for cheaper, heavily built instruments.

[Wrnchbndr]

Mando going out of tune? Unless its all of the strings, most of the time, the problem is either the nut or the bridge.
Always tune using a tuner. Never tune by ear as one string that sounds sharp may be the result of another going flat or the reverse and if you make the wrong choice, you'll have two strings that are out of tune instead of one.

Here's my method.

One string at a time...
1. Tune the string to pitch using an electronic tuner or a phone app.
2. TEST A: Press down on the length of string between the nut and the tuner post to make the string go a half-step sharp and release.
3. Using the tuner, see if the string remains slightly sharp.
4. TEST B: Gently give a tug on the string between the nut and the bridge or attempt to bend the note by a half-step sharp.
5. Does the electronic tuner now indicate that the string is flat?
6. Repeat the process going back and forth to get a fair understanding of the differences between TEST A and TEST B and write down the average difference in pitch for that particular string.
7. Do this to all of the strings and you'll see which strings are the major offenders.

A perfect nut will remain in tune after both TEST A and B but perfect nuts don't really exist. What is desirable is that the string flow through the nut slot and an increase in tension between the tuner post and the nut be immediately passed over the nut to the major length of string. Excessive friction or restriction in the nut slot leaves a slight amount of reserve tension between the tuner post and the nut resulting in the string eventually going sharp as the tension slowly becomes balanced (if you always "tune up to pitch"). A difference of 3 Cents between A and B on an electronic tuner is okay. A difference of greater than 10 Cents is a problem that should be be repaired and it can sometimes be difficult.

It can be very difficult to get a nut slot to behave and its complicated by the left or right-handed bend that the string makes toward the tuner post as it leaves the backside of the nut. To a lesser extent, the same sort of restriction issue can happen at the bridge and you can perform the same basic test but its rare.

Don't go looking for a problem. Don't try to fix something that isn't broken. If you don't have a noticeable issue with your mando or guitar going out of tune, leave it alone. This is a test I perform during a setup.

[derp]

Thanks to everyone for the in depth replies. I haven't had much time over the holiday season to mess around but began yesterday.

I found that on my A and E strings I had wrapped the string around itself on the tuner post. I also removed the strings and cleaned out the slots in the nut and bridge, there was a bit of gunk.

I had a look another look at the tuning of the strings and noted that even when in tune with itself based on a tuner, the D A and E strings were out from each other (across the 7th fret). I looked into this and when I play on the twelth fret all the strings sounded sharp except for G. This makes me think it is possibly a bridge issue. It actually fell off when I changed strings about a year ago and I put it back in the approximate position.

Finally, I had another look at the machine heads with strings removed. There is a lot of discrepancy between them, some turn easily, some with much greater difficulty and one actually changes as it rotates. 3 of them were loose to the point that a lateral inward force on the tuning knob causes it to shake around a heap. In these 3 the tuning post also has a heap of movement. I tried looking for a way to tighten these heads in particular, none seemed to work. I took of picture of the machine heads posteriorly but am not sure how to upload here.

Today I am planning to put a new set of strings on and sort out the bridge position so it is in tune with itself.
If anyone has any ideas it would be much appreciated.

Thanks and happy new year !

[Br1ck]

I also take a #2 pencil and work some graphite into the nut slots.

[MikeEdgerton]

Make sure the orientation on the saddle (bridge top) is correct or you will have intonation issues. You also have to make sure the bridge is in the right position. Don't assume the worn spot from where it was is correct.