Re: Another vintage "tater-bug".
Disagree with FretNot; it's more difficult to adjust tuners with a low gear ratio than "better" ones with a higher ratio, but you can still make "small incremental adjustments." Just requires a more precise manipulation of the tuning button. After all, violinists have been making small incremental adjustments in tuning for centuries, without any gear ratio at all -- just a "1:1" friction peg.
It is possible that the tuners could be slipping, or that the strings could be binding and not moving smoothly through the nut slots. I've found as a general rule that tuners on older instruments were pretty well-made, even on the "mid-range" mandolins that sold for $10 or so around 1900. A bit of lubrication on the tuners might improve things, or perhaps a bit of graphite in the nut slots.
Nearly all mandolins have "open" tuners, where the worm and the gear are exposed, and as a result dirt and damage are more common than with tuners that have housings to protect their "works." From the pic, these tuners seem pretty standard for instruments of that vintage, and should be workable if cleaned and lubed. Good luck.
Allen Hopkins
Gibsn: '54 F5 3pt F2 A-N Custm K1 m'cello
Natl Triolian Dobro mando
Victoria b-back Merrill alumnm b-back
H-O mandolinetto
Stradolin Vega banjolin
Sobell'dola Washburn b-back'dola
Eastmn: 615'dola 805 m'cello
Flatiron 3K OM
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