In the beginning I used guitar and bass tuning machines, scavenging
them of old guitars or buying cheap ones. When I began to build a
twenty-five string dulcimer I realized I needed to make my own.
Four-plus sets of tuning machines were more than I wanted to buy and as
I was planning to use music wire for the strings, they most likely
would have broken anyway. The big dulcimer never worked (the tension
required to tune it bent a very beefy frame –one that would have
supported a mid-duty trailer), but it taught me a few lessons, one of
which was how to make tuning heads (another was why so many traditional
instruments are tuned by moving the bridges).
I drill a 1/8 hole in the shaft of a 3/8 bolt. I tap the pinblock or
headstock or whatever you want to call it to receive the bolt and use a
locknut of some sort to hold it when tuned. It takes two wrenches to
tune a string, but it isn’t as bad as I’d have thought. Recently I
discovered belleville disc spring washers which I use under
the pinblock. This has made the tuning process way less
grief-intensive. Using fine thread bolts might be better, but the
coarse ones were cheap and I had a box of them. I used 3/8 because they
were easier to drill than 1/4 would be and (on the dulcimer) I was
planning to use .125 music wire for the low strings (didn't work) and I
wanted as much strength as I could get. Mostly now I use
1/4" bolts for the pegs as it saves a lot of space.
At the tail end I use a 1/4 bolt as a pin and there is some fine tuning available from it.