The attached image shows the simple sliding door (red). It's rotated about 6 degrees and is supposed to move along the glide (narrow white rectangle) as indicated by the blue arrow on the left.  Moving in z only, it moves as shown on the right.  The relationship between x and z is simple trig, so lesbentley's suggestion will work and that is what I'm planning.  All movement will eventually be via ERC dials, so all this will be invisible in the end.  However, I usually get lost in the various levels of controls while I'm building them and would prefer them as simple as possible.  It would be so nice if the door would move along its internal axis as shown by the thin black cross hairs in both views. 

Thanks for all the interest.

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