Internal Drawers as an Alternative to Blum Tandembox — Compatible & Matching

An internal drawer is a pull-out system concealed behind the main cabinet front that organises storage space in base units and can be retrofitted via standardised hole patterns as an alternative to existing systems.

Internal Drawers as an Alternative to Blum Tandembox

When repairing or expanding kitchen base units, installers and joiners frequently face the task of replacing defective components or creating extra storage space. When existing systems become worn out or an existing cabinet needs to be retrofitted with internal drawers, completely replacing the carcase units is usually uneconomical. Instead, accurately fitting drawer systems are used as compatible alternatives to Blum Tandembox or similar industry standards.

The crucial factor for a smooth replacement or retrofit is technical compatibility. This is determined not by the brand name, but by the drilling pattern, internal cabinet width, and installation depth. Modern hardware systems are engineered to fit seamlessly into the standardised grid dimensions of the furniture industry.

Technical Requirements for Compatibility

To integrate an internal drawer suitable for Blum systems or other established brands, the dimensions of the cabinet carcase must be measured accurately. The furniture industry predominantly works with the System 32 standard. This means that drill holes in the side panels have a vertical spacing of exactly 32 mm from centre to centre. The distance from the front edge to the first row of holes is generally 37 mm. If the new runner slides support this hole pattern, direct installation is possible without the need for time-consuming re-drilling.

The second critical dimension is the internal carcase width. Kitchen base units have standardised external widths, but the internal width varies depending on the thickness of the side panels (usually 16 mm or 18 mm). A kitchen cabinet pull-out 60 cm with an external carcase width of 600 mm and a side wall thickness of 16 mm requires an exact internal installation width of 568 mm. If the wall thickness is 18 mm, the internal dimension reduces to 564 mm. Compatible internal drawers feature tolerance adjustments on the runners or drawer sides to bridge these millimetre differences during installation.

For narrower cabinets, which are often used as alternatives to larder pull-outs or for spice storage, the same calculation principles apply. A kitchen cabinet pull-out 40 cm or a kitchen cabinet pull-out 30 cm must be matched precisely to the remaining internal clearance so that the runners operate parallel and without tension.

Matching Runner Systems and Nominal Lengths

In addition to the width, the nominal length of the runners is decisive. Kitchen base cabinets feature a standard carcase depth of approximately 560 mm. Runners with a length of 500 mm are typically used here. For shallower cabinets, such as those positioned in front of service ducts or pipework, shorter variants such as drawer runners 400 mm must be used.

When choosing the mechanism, a distinction is made between two fundamental types: A full extension runner can be pulled out 100% from the cabinet. This allows unhindered access right into the furthest corner of the drawer, which is essential for deep kitchen base units. A partial extension runner, by contrast, only exposes around 75% of the drawer depth. Anyone looking to provide a full replacement for an existing system generally chooses full extension drawer runners, as these meet modern ergonomic standards in furniture construction.

Damping and Mechanisms: Soft-Close and Push-to-Open

A frequent reason for replacing hardware fittings is defective damping elements. When fitters are looking for a replacement for Blum dampers, it is important to understand the mechanics of the runner system. Damping in modern slides is often integrated directly within the runner housing and operates via a hydraulic or pneumatic cylinder.

When closing the drawer, an activator engages with the damping mechanism. Kinetic energy is absorbed, and the drawer closes smoothly and silently over the final few centimetres. This mechanism is known as soft-close. If the damping of an old system fails, the entire slide is usually replaced with soft-close drawer runners that serve as a compatible alternative.

Push-to-open technology is completely distinct from this. It is used on handleless fronts. Pressing the front tensions a spring that subsequently pushes the drawer outward. Soft-close and push-to-open are contrasting mechanisms. Anyone planning handleless internal drawers requires push-to-open drawer runners. Combining both systems within a single standard runner is technically complex and uncommon for standard retrofit projects.

When storing heavy pots, pans, or food supplies, the load capacity must also be considered. Standard drawers are often rated for 25 kg to 30 kg. For heavily loaded internal drawers, installing heavy-duty drawer runners capable of supporting loads of 45 kg or more without deflection is recommended.

Retrofitting an Internal Drawer: Grid-Based Installation

Retrofitting internal drawers requires precision. Installation resembles a modular construction kit, where the runner slides must engage accurately with the existing grid. If the System 32 hole pattern is already pre-drilled in the carcase, the installation effort is reduced considerably.

Tools Required

• Pozi screwdriver (PZ2)
• Cordless drill/driver
• Tape measure or folding rule
• Spirit level
• Centring drill bit (if new holes must be drilled)

Installation Steps

1. Determine positioning: Plan the height of the internal drawer. Pay attention to the hinges on the main cabinet door. The drawer must not collide with the hinge cup or mounting plate when pulled out.
2. Mount the runners: Position the carcase runners against the side panels. For pre-drilled hole patterns, special Euro screws (Ø 5 mm) are used. If the runners must be screwed into undrilled wood, wood screws (Ø 3.5 mm or 4 mm) are utilised.
3. Check alignment: Use a spirit level to ensure both runners are perfectly horizontal and mounted at the exact same height (in the same grid hole).
4. Insert the drawer: Place the drawer box onto the runners. With undermount drawer runners, the drawer is fitted from above and clicked onto the locking clips on the underside.
5. Fine adjustment: Using the adjustment wheels on the locking clips, the front of the internal drawer can typically be adjusted in height and tilt by 1.5 mm to 2 mm until the gap reveal runs parallel.

Frequently Asked Questions (FAQ)

How do I find matching replacement parts for Blum hinges or drawers? Look for components that are compatible with Blum. Focus primarily on the technical specifications: the nominal length of the runner (e.g. 500 mm), the load capacity (in kg), and the hole pattern (System 32). For concealed hinges, the cup drilling diameter (usually 35 mm) is the decisive criterion.

Can I install an internal drawer in any base unit? Yes, provided the internal clearance width is measured accurately and no obstacles such as waste traps or internal gas struts obstruct the path. It is vital that the door hinges do not obstruct the drawer path. Hinges with an opening angle of 155° or 165° are often required so that the door swings completely clear of the drawer trajectory.

What should I do if the cabinet soft-close damper is defective? In drawer systems, the damper is usually built directly into the runner slide. Individual replacement of the hydraulic cylinder is rarely supported. In this case, the entire carcase runner is replaced with a compatible slide featuring integrated soft-close mechanics.

Which screws do I need for mounting the runners? If the cabinet has pre-drilled 5 mm hole rows, use Euro screws. For direct fastening into chipboard or MDF without pre-drilled holes, use countersunk wood screws (PZ2 or TX drive), typically sized 4 x 16 mm.