I recently discovered Spaceballs as a tool for aligning floating panels. Spaceballs, as the name implies, are small rubber balls that fill the expansion gap around a panel. The panel compresses the ball. Since there are Spaceballs in the gaps all around the panel, the panel is pushed into the center. Each ball compresses roughly the same amount. The panel resting spot becomes the absolute center.
Panel expansion is still possible since the Spaceballs can be compressed further if they are subjected to a greater force. Different sizes are available to allow use of Spaceballs with a multitude of panel thicknesses and groove depths.
The beauty of Spaceballs is their ease of use. Simply insert two or three into each rail and stile and assemble the door as you normally would. The panel get centered automatically. In my shop this results in big time savings and superior results. The only way to make a mistake is to forget to insert the Spaceballs.
Spaceballs are priced according to quantity. Below 5,000 pieces they are only a fair value. Above this threshold you will be paying cents a door for many minutes of time savings during assembly and perfectly center panel that will stay aligned for the life of the piece.
Spaceballs are a homerun for woodworkers.
Sold at: Spaceballs.com