Loose tuners

[dwc]

The tuners on my mandolin are loose (for lack of a batter term). When tuned up to pitch they fine. When raised to pitch they are tight and hold tune, but when I down tune or remove a string, the tuner knobs (not the buttons) and pegs are loose or have “slop”. I am taking it to a luthier I trust, but I wanted to know if anyone can diagnose the issue.

[sunburst]

Depending upon the brand of tuner it can be normal or it can be loose screws. In order to tune correctly and stay in tune we must tune 'up' rather than tune 'down', as you said.
If the tuners are older Gotoh deluxe, some looseness is built in. It makes the tuners more tolerant of misaligned or inaccurately spaced holes in the peghead when tolerances are made a little looser.
If the tuners are Waverly or other tighter brands, it could be that someone has loosened the screws holding the gears to the posts to introduce some looseness in order to make the tuners turn easier rather than bind in poorly drilled holes. Many people do this and consider it an "adjustment".

If you find that the tuners are not "adjusted" with loose screws, there is probably nothing wrong with them. Simply continue to tune 'up' rather than tune 'down'.

[Richard500]

DWC, if I understand how these things are designed, it’s the string tension that pulls the little gear into tight contact with the worm; hence ‘worm over’. There should be no problem with the parts if they are loose without strings. The post is a lever. Top pulls down, bottom pulls up.
My old mandos have ‘worm under’ and other arrangements, but the ‘worm over’ is obviously the sensible way to do it all since these mechanisms are in no way free of slop, and do not need to be.
Not to say that a particular one, or a brand can’t be just too sloppy, or that the holes or bushings can’t be drilled wrong, but basically, it’s plenty good. The totally junk tuners (with 1” spacing) I bought recently were so badly made that they literally could not work.
While I’m at it, the ancient Bohmann that I just started working on, has a boxed variety (patent pending!) where the post shaft is supported by the outer plate, and maybe by the inner (haven’t opened it so far, things may fall apart), which is just another way to do it. Nice flat plate, a good place for fancy engraving.

[sunburst]

DWC, if I understand how these things are designed, it’s the string tension that pulls the little gear into tight contact with the worm; hence ‘worm over’...

In reality, that is not quite how it works.
When tuners are properly mounted, the string posts are deflected by string tension, but rather than forcing the gears together (or apart) there are two bearing surfaces that support the post. One is the hole in the tuner plate and the other is the peghead bushing. The post is deflected to a slight diagonal (away from perpendicular to the tuner plate), but the bearing surfaces limit and control the amount of deflection so that the gear mesh is only slightly affected by the string pull. Once again, this assumes well spaced and well aligned peghead holes and properly installed tuners and bushings.