From guitar experience I know that instruments goes out of tune over time but they always become loose and go flat. My mando goes out of tune and more often goes sharp! How do you explain going sharp which means strings are being pulled more instead of getting loose?
Just to give you a little background info:
To improve tuning of my mando I had changed the tuners for grover 308 F-style (since I could not find any good A-style tuners. The two top knobs were sticking out looking funny on the narrower top of headstock so I turned them around and installed them upside down. Still this does not explain getting tighter.
Do all of the strings go sharp approximately the same amount? If so, it may have to do with relative humidity. Do some go sharp and others not? Does one string of a pair go sharp and the other not? If so, the nut slots are probably cut poorly.
They all go sharp, but not exactly at the same rate. What could humidity got to do with it? That's an interesting theory.
I am not sure about mechanisem of tuners. Do they work in one direction the same as the other? I have heard that always tune up not losen the knob to tune the instrument. So I guess directions has something to do with it. Could it be becasue I have installe them upside down? (I could play for a few days while standing on my head to check but it would be easier to ask someone )
You got the right answer from John above.
Increasing humidity swells wood, raises the top & bridge, and increases tension of the strings. Pitch goes up. Sometimes if nut slots are too tight, the strings might not slide evenly and so the difference among the strings. Very common phenom.
Most fascinating information. Are there any tricks to keep the humiduty problem under control (I mean in the case, room I can guess)? Is there an optimum level?
Optimum relative humidity: 40% to 50%. In-case humidifier, or desiccant package, with a hygrometer to keep track of what's going on.
We just have to live with some tuning changes from RH changes.
Most of the time it is the strings binding in the nut slots, that cause strings to go sharp. If they don't slide freely through the slots in the nut, the following happens.
When you tune a string to pitch, the tightening starts between the tuner and the nut. If the string binds even the least bit in the nut slot, when you reach the pitch you want, this is what is actually happening to the string itself. It has a slightly higher amount of tension between the tuner post and the nut, then a little less tension from the nut to the bridge, and possibly even a little less tension from the bridge to the tailpiece. As you play, the binding string pulls loose enough, to even out the tension down the string length, because of the pressure of your fingers fretting strings, and your pick striking the strings. By the time the tension gets evened through out the string, you are out of tune.
The notches in the nut, and the bridge both, must be cut correctly for the size of the strings you are using, and the notches also must be cut at the correct angles. Even after that is done, it sometimes helps to use some sort of lubricant on the nut slots.
Sorry to be so wordy, but it's hard to describe this stuff so that it is understandable.
Gene Warner
retired repairman
Lubrication is not needed in correctly fit nut slots, strings do not normally move through the bridge slots during tuning (after initial stringing and "settling in"), so no lube is needed there.
Interesting problem with my tuners
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