Having the correct drawer runner setback on Blum Tandems makes for a very nice product installation. So what is runner setback? It is how far the leading edge of the cabinet profile on the Tandem is set back from the front edge of the face frame or if you are building cabinets without face frames the setback is from the front edge of the cabinet side panel. If you are building cabinets with overlay drawer fronts the runner setback is 3mm or 1/8 of an inch. (There is one exception. The Blum Tandem Edge has a 4mm setback. We will not discuss the Tandem Edge in this article.)
As mentioned in the first paragraph all overlay drawer fronts for tandem runners require a 3mm setback. What though, is the runner setback when building cabinets with inset drawer fronts? One would think that it is a simple matter of adding drawer front thickness to runner setback for overlay drawers. Not so fast. There are three things that affect runner setback.
1) The locking device being used.
2) Sub-front thickness
3) Drawer front thickness.

The most highly recommended and best-selling locking device for inset drawers is the depth adjustable BT51.1901.PS.

Using a formula for calculating runner setback using BT51.1901.PS
• B563H, B563., B569H, and B569.
o Sub-front thickness + Drawer front thickness minus 9mm (11/32”) = runner setback.
• B563F, B563A, B569F, and B56A.
o Sub-front thickness + Drawer front thickness minus 12mm (15/32”) = runner setback.

For all other locking devices use the following chart and formulas;

Using a formula for calculating runner setback using the four locking devices above;
• B563H, B563., B569H, and B569.
o Sub-front thickness + Drawer front thickness minus 11.5mm (7/16”) = runner setback.
• B563F, B563A, B569F, and B56A.
o Sub-front thickness + Drawer front thickness minus 14.5mm (9/16”) = runner setback.

Inset drawers are beautiful. Use the above information to create your masterpiece.