In the attached sketch you'll see the major parts:
* 12 inch section of Harken 1 inch recirculating ball track
* Harken car to fit the track (tapped to hold a 5/16th" NC bolt)
* teak - base containing a 5/16th NC bolt, a stainless steel spring (1" x 3" or so)
* teak - cap (for the base)
* teak - transition from Harken Car to the plotter arm