Here is another redneck linear with a little more power. Uses standard continuous rotation Servo, 1/4-20 all thread and has bearings on the spool. Should have many applications in robotics and home automation.
This linear has a one to one gear ratio and has travel of .050 inches per servo rotation. That give a travel of about 2.7 inches per minute with the Pololu 1248 (SpringRC SM-S4303R, Jameco 2128201 $13.95) continuous rotation servo. I do not have one, so have not tried it but, Parallax makes a high speed CR servo that is way faster (180 RPM), that would make the linear travel 9" per minute (Parallax 900-00008).
This design uses standard 1/4-20 nuts inside the spool to move the all thread rod. Uses two 18x12x4mm RC car/truck bearings on the spool. Yoke holds the rod fixed with a 1/4-20 nut, the gear and motor move the all threaded rod. Uses #4 sheet metal screws for fasteners and #6 machine screws for yoke pins.
Since continuous rotation servos work on speed and time this type of linear would need micro switch cut off if traveling long distance and ending up in an exact spot.
The servo gear is for standard 25T Futaba spline. If you need other servo spline sizes let me know.
Still having trouble with threads, you will have drill to .200" and run a 1/4-20 tap in the yoke for threads.