Slipping strings are a major cause of tuning problems. Ensure you are properly winding your strings around the machine head posts so they do not slip and loose tension.
Too many winds will cause the string to slip. For that reason, when fitting strings, cut the string 30 – 40mm over length. This produces about 3 winds around the post.
New strings need an opportunity to stretch. So when winding the strings, gently pull back on them, this will ensure that the string is tightly wound around the post.
A newly fitted set of strings will probably require several re-tunes during their first day of play before they settle read more
When tuning, do you hear a repetitive creaking or clicking sound? If a slot in the guitar nut is too small for the string gauge being used, the string will bind and catch in the slot. A slight adjustment to the width of the slot is necessary. Read more here
When installing strings on an acoustic guitar it is important that the ball end be firmly seated and locked between the bridge pin and internal bridge plate. If it is not, the ball end of the string may pull the bridge pin upwards loosing its grip within the bridge pin hole. This will result in the strings anchorage being comprised and the string going out of tune.
A few other possible causes for an instrument to loose its tuning
- Weak or poorly constructed neck/body joint
- Loose or broken internal bracing
- Poorly fitted or loose machine heads
- A bridge saddle that is too loose inside its slot
- Poorly fitted bridge
- Loose tail piece
- Poorly set up tremelo unit system