I'm looking for ideas for sliding a ~2" ferrite core in and out of a
coil. I've seen ways of tuning over a small range by means of a brass
screw used as core. I need smtg better than that, with repeatable
positioning and smooth movement.

Some ideas:

- micrometric screw:
use a preexisting screw taken from old depth gauge or bought
standalone
PRO calibrated, demoltiplicated, high resolution position readout
CON expensive if new, still need to invent a way to fasten ferrite
core to spindle, screw protudes.

- screw drive from scratch:
PRO can be taylored, can use knob with 360deg scale, turns determined
by screw pitch - say 0-100 over 360deg @ 20 turns/inch produces 8,000
divisions over 2" linear displacement (if with vernier reaches
80,000), may use knob with turns counter
CON quite complicated to design, may reguire machining and searching
for pieces.

- wire drive, like in old radios
PRO can reuse hardware like in old radio, if scale is linear-motion
the tuning indicator is directly attached to ferrite plunger
CON may suffer backlash, hardware disappearing, very short scale.

I only saw very rough solutions, such as gravity pulled ferrite in
vertical coil, or using brass screw directly as core for small band
coverage. No idea if there's some promising and available type of
surplus drive.

Any ideas? Any plans anywhere for DIY? Kits???

(again, I _did_ see use of a small brass screw w/o ferrite!).

R & TIA

Filippo N1JPR