Front Extension as an Alternative to Blum Tandembox — Compatible & Suitable

A front extension is a drawer system where the furniture front is connected directly to the metal drawer sides and runner profiles, with compatibility for existing carcass systems primarily determined by the System 32 hole pattern.

Front Extension as an Alternative to Blum Tandembox — Compatible & Suitable

In furniture construction, kitchen installation, or cabinet repairs, finding suitable replacement fittings is a frequent consideration. When drawer runners become worn or a kitchen base unit requires retrofitting with new extensions, an alternative to Blum Tandembox is often sought. Replacing or planning these units requires precise knowledge of installation dimensions, load capacity, and the mechanical compatibility of the components.

A direct exchange of individual parts — such as just the left-hand carcass profile — between different manufacturers is generally not possible due to proprietary locking catches on the drawer base. However, if the entire drawer interior is renewed, compatible drawer systems can be installed without issue, provided the carcass dimensions match.

What to Consider for Compatibility

To ensure a new front extension fits existing kitchen cabinets, the mechanical interfaces of the furniture carcass must be taken into account precisely. The system of pre-drilled hole lines inside the unit serves as an architectural foundation that determines the positioning of the fittings.

• System 32: Most industrially manufactured furniture relies on this standard. The pitch between drilling centres is exactly 32 mm, and the distance from the front carcass edge to the first hole line is 37 mm. Compatible carcass runners utilise this grid dimension for fastening.
• Nominal length (NL): This describes the length of the runner profile and the drawer side panels (drawer sides). Standard dimensions for kitchen base units range between 450 mm and 500 mm. For shallower cabinet depths, such as in bathroom furniture, drawer runners 400 mm or shorter are frequently used.
• Internal carcass width: The clear internal width of the cabinet minus the material thickness of the side panels (usually 16 mm or 19 mm) determines the exact width of the drawer base and the rear panel.

Suitable Extension Systems for Cabinet Making

When selecting fittings, technical performance is paramount. For a sturdy front extension, particularly when storing heavy cookware or provisions, concealed under-mount drawer runners are the technical standard. They are mounted invisibly beneath the drawer base and provide exceptional lateral stability.

Extension Types and Dampening

A key factor in kitchen ergonomics is extension length. A full extension runner pulls out 100% from the carcass, allowing clear access right to the rearmost corner of the drawer. In contrast, a partial extension leaves roughly 25% of the drawer inside the cabinet. For modern kitchen frontals, full-extension drawer runners are the technically superior choice.

Additionally, closing kinematics are determined by dampening mechanisms. Drawer runners with dampening (often referred to as soft-close) brake the momentum of the drawer over the final few centimetres, pulling it gently and silently into its final position. This mechanism should not be confused with push-to-open (tip-on), which causes handleless frontals to spring outward upon pressing the front. Both systems operate via opposing mechanical principles.

Specific Cabinet Widths and Applications

The sizing of the extension depends on the overall carcass width.

• A kitchen cabinet extension 60 cm is the standard size for hob base units, pots, and pans. Here, attention must be paid to adequate dynamic load capacity (e.g., 30 kg or 40 kg).
• A kitchen cabinet extension 40 cm or 45 cm is frequently used for integrated waste-sorting systems. When fitting a waste bin within a front extension, the height of the sides (gallery rails or enclosed glass side elements) must be chosen high enough to stabilise the bins laterally during rapid opening.

Installation and Retrofitting: Fitting the Front Extension

Installing a complete drawer system as a replacement for existing extensions requires precise workmanship and the correct tools.

Tools required:

• Cordless screwdriver
• Pozi-drive bit (PZ for chipboard screws)
• Tape measure or folding rule
• Carpenter square
• Bradawl or 5 mm wood drill bit

Step-by-step installation:

1. Dismantling: Remove the old drawer and unscrew the existing carcass profiles.
2. Runner installation: Position the new carcass runners along the System 32 hole pattern on the cabinet interior. The front edge of the runner is typically positioned 37 mm behind the front edge of the carcass. Secure using 4x16 mm chipboard screws or Euro screws.
3. Drawer assembly: Screw the 16 mm chipboard drawer back panel to the metal drawer sides. Slide in the 16 mm thick drawer base and fasten it from below through the side profiles.
4. Front attachment: Mark out the position for the front fixing brackets on the rear of the furniture front, screw the brackets in place, and clip the front onto the metal sides.
5. Fine adjustment: Use the integrated eccentric adjusters within the drawer sides to align the front in height (typically ± 2 mm) and side-to-side (± 1.5 mm) until the reveal gaps run perfectly parallel.

Frequently Asked Questions (FAQ) on Compatibility

Can I replace individual dampeners on drawers? With modern under-mount runners, the soft-close cylinder is permanently integrated or riveted into the carcass profile. If the dampener fails, the complete carcass runner must generally be replaced. Clip-on dampeners are usually only available for concealed cup hinges on standard hinged doors.

Do Furnica runners fit into the drill holes of Blum extensions? Yes, provided both systems utilise the standardised hole line grid (System 32). While the horizontal screw hole positions may vary slightly between manufacturers, the vertical spacing (32 mm) and setback (37 mm from the front edge) are standardised. Replacing the complete drawer runner system is therefore straightforward.

Can I upgrade drawers from partial extension to full extension? Yes. If the nominal length (e.g., 500 mm) and internal carcass dimensions are identical, a partial-extension runner can be removed and replaced with a full-extension runner at the same fixing points. The drawer box itself will usually need to be replaced with the matching model for the new runner system.

What is the difference between a roller runner and a ball-bearing slide? A roller runner uses nylon rollers running on an epoxy-coated metal track (common in simple, bottom-mounted partial extensions). A ball-bearing slide consists of interlocking metal profiles with steel ball bearings. It is more compact, handles higher loads, and is often mounted to the side of the drawer. Under-mount runners, by contrast, typically employ cylindrical rollers housed within a carriage running underneath the drawer bottom.