Not quite  guitar but I guess the science is all the same.  The trouble with this one, it’s not staying in tune.

The only way to increase the tension is to screw the keys in a little tighter.  Trouble is if I do that I think the keys will just split.  Once of them has already been replaced and the other 3 are badly cracked.

A new set then.  They’re a little larger so I needed to drill the holes out a little..

There we go.  The keys are a little larger but at least they all match and it’ll hold its tuning now..

  If there’s anything else you need just check out the website www.guitar-george.co.uk