I thought for sure the last idea would completely solve my racking problem - those new linear trucks are really tight and smooth - BUT sure enough, once I put everything together - I could still rack the gantry about an inch... So I jumped on CNC Zone and posted my dilemma - and thankfully BigMike reminded me of THIS thread concerning the racking problem. So I ran down to Home Depot and bought some wire rope and some turnbuckles and implemented the idea... Luckily I had room on the bolts that are holding the trucks together for the cable bearings (which if you notice I've switched to the patio door bearings for the rail rather than the Butcher Boy bearings from last post) the patio door bearings have a lot less slop and fit perfectly onto 1/4" round steel  - but the Butcher Boy bearings are perfect for the wire rope idea :) I drilled and tapped the legs to hold the eye bolts, ran my wire rope and anchored it on two legs and then ran the rope though the eye bolts at the other end and attached each to a turnbuckle in the middle so I could tension up the cable... Now I cannot rack the machine at all! Finally I think I can move on! :)

Edit: I have since swapped out the patio door bearings with some home made V bearings because even the patio door bearings just had too much play to be good

Here's the pictures - they really tell the story as usual and there's a video below them that shows the movement... I also included a few shots of the Shopsmith in drill press mode - just because I think it's cool :)

Patio Door Bearings Patio Door Bearing Linear Truck Linear Truck Drilling Holes for Extrusion Shopsmith in Drill Press Mode Truck and Cable InsideTruck and Cable Outside Truck and Cable Underside CNC Underside CNC Front Linear Truck Cable Anchors CNC TopCNC Top CNC Back

Gantry Moving Video