Wobbly Axis on Machine, Any Suggestions?

[idtkid]

I have a 4' x 8' diy 3 axis CNC router at work that I designed and built. It has a steel frame and is almost exactly identical to the older ShopBots seen HERE The problem is that on the 2nd longest axis (the one crossing the bed) the end opposing the stepper motor is not rigid. It vibrates and moves with the momentum it has from the Z axis. I tried hooking up tracks and bearings that I could place tension on that end of the axis but it bound up with trying to jog.

How did the old ShopBots stay rigid with only 1 motor on that axis?
Is my only solution to buy another motor, drive, rack and pinion and drive that side in harmony with the other? Thanks in advance, Ill snap pics if you need them.

[ZNAK]

do you have backlash in rack and pinion?

or your construction not 100% identical to ShopBot?
it is better to see your pics if problem is not backlash.

[BobF]

I am no expert, but I don't see any other solution.
Post some pictures.

[idtkid]

Long overdue update: I didn't realize that Shopbot's had a second motor slaved on the opposing side of the X-axis :x huge noob mistake on my part but I learned lots and the machine is rock solid now.