I've noticed one strange thing about my variety of Cube3 printers... some have a really good magnetic lock on the build plate and some are only tepid.

I did this Thingy a long time ago. Basically a lattice with 8 glue points and fixed magnet locations. The fit is snug. If anything, the holes for the magnets need a light sanding but it is intended to allow no play. Not so tight as to pull caps of the magnets. Be sure to fit the print to the magnet cluster before committing it to the build plate.

I highly recommend using ShoeGoo for this. It cleans up easily if you change your mind and it just works. A small dab, just a scraping off of a shallow dome from the tube of ShoeGoo on each pad is more than enough. Place the PlateLock frame on the Cube's magnets, just a little low, and place the plate as squarely as you can in the Cube3. Now carefully raise the PlateLock to meet the plate while being careful to keep the plate aligned on the magnets correctly. While the plate is forward, press the 3 accessible pads to the build plate. Carefully! move the plate to the other end and do the same for the back 3 pads. Then tip your printer so you can put pressure on the two pads on the sides. Check, rinse, repeat to meet your own level of perfection.

If you don't like ShoeGoo or only have an RTV on-hand, it will also work wonders. Just a bit harder to clean up if needed.

EDIT: For a simpler attachment, use tenacious double sided tapes - More info here: http://www.print3dforum.com/showthread.php/4489-Built-Plate-Stabilizer

3D Systems

Cube 3

No

No

0.2

any

See the included cube3 file. Left side PLA.