My wife, Judy, is a professional musician (cello). All classical musicians who play stringed instruments (violin, viola, cello, double bass) get calluses on the end of their left hand fingers (the right hand holds the bow). They need those calluses in order to be able to play their instrument for a couple of hours in a performance, as well as for the hours of rehearsal prior to the performance, and for their everyday practice. They have to practice every day in order to maintain those calluses, as well as to learn the music for the next performance.
However, Judy and I occasionally take a trip of up to three weeks where she does not have access to an instrument and her calluses fade away. Rebuilding those calluses takes time after we return so she cannot do a performance for several weeks after we return.
To help her maintain her calluses, I made a practice piece, sort of a scaled down cello neck. While a cello has four strings, the practice piece has only two, but that's sufficient. She can run the fingers of her left hand over the strings, pressing them down, as she would when playing - and therefore maintain her calluses. (I must admit that sounds really boring - like running on a treadmill or peddling a stationary bike.)
Here's a picture of what I made for her. It's not as "fine" as her cello, but it will work. I thought of carving a scroll on the end of the piece, and may do it one day. I should also polish the ebony a bit more, to a mirror shine.
First, a view from the side, showing the pegs. The pegs are made from cocobolo and the peg heads are on the side away from her head when she uses it (the head of the cello goes on the musician's left shoulder). The strings are ones that she replaced on her cello.
Practice-strings-01.jpg
And a view from the top - you can see into the pegbox. The finger board of most stringed instruments is ebony and I used ebony on top of maple for this piece. I used too much taper on the pegs, but they work with some effort - after I tighten one, while I'm still holding the tension, I tap the peg into the pegbox. If I don't do that, the peg can unwind.
Practice-strings-02.jpg
Judy will try it out on our next trip. I hope it works well for her.
Mike