Blum Tandem Undermount Drawer Slides Installation Guide

Updated November 11, 2026

Installing Blum Tandem undermount drawer slides requires precise measuring, a locking panel for the drawer bottom, and a specific sequence of steps to ensure smooth, self-closing operation. These slides are popular in high-end cabinetry because they mount beneath the drawer, leaving the sides visible, and offer a soft-close feature that prevents slamming. This guide covers the full process, from understanding the components to troubleshooting common issues, so you can install them correctly the first time.

Background and Why Choose Blum Tandem

Blum Tandem slides are part of Blum’s concealed runner system, introduced in the 1990s as a premium alternative to traditional side-mounted slides. They are known for their durability (tested to 100,000 cycles by the manufacturer), smooth action, and the ability to carry heavy loads—up to 70 kg (154 lbs) for the strongest variant. Unlike side-mount slides, Tandem slides attach to the bottom edges of the drawer box, which means the drawer sides are fully visible and can be made of any material, including thicker wood or decorative panels. The system uses a locking mechanism (often called a “locking cone” or “expansion peg”) that connects the drawer to the slide, and it requires a specific drawer bottom thickness and a locking device for the release lever. This design is favored in custom kitchens and furniture because it allows for a frameless, modern look and offers a 3-way adjustment (height, side, and depth) for perfect alignment.

Tools and Components You Need

Before starting, gather all necessary tools and verify you have the correct parts. Blum Tandem slides are sold in pairs, and each pair includes the left and right slide, but you must also purchase the correct locking devices (often sold separately) and the drawer bottom locking plate. Here is what you will need:

Blum Tandem slides (choose length based on drawer depth, e.g., 450mm, 500mm, 550mm, etc.)
Locking devices (also called “locking cones” or “expansion pegs”) – these come in two versions: one for drawer bottoms of 16mm and one for 18mm thickness.
Drawer bottom locking plate – a plastic plate that attaches to the drawer bottom and clicks into the slide’s locking mechanism.
Drill with appropriate bits – typically a 5mm bit for pilot holes and a 10mm bit for the locking device hole.
Phillips screwdriver or impact driver – for screws (usually #6 or #8).
Measuring tape, square, and pencil – for precise layout.
Clamps – to hold the drawer box while drilling.

Make sure your drawer box is constructed correctly: the drawer bottom must be at least 12mm thick (for the locking plate) and the drawer sides must be flush with the bottom. If your drawer bottom is thinner, you may need a reinforcing panel.

How the System Works

Understanding the mechanics helps avoid mistakes. The slide consists of a fixed rail (mounted to the cabinet side) and a moving rail (attached to the drawer). The moving rail has a curved track that creates a slight upward motion when closing, which activates the self-closing mechanism. The locking device is a small plastic piece that fits into a hole drilled in the drawer side near the bottom. It has a cone-shaped head that slides into a slot on the moving rail. When you push the drawer closed, the cone engages with a spring-loaded clip, pulling the drawer shut and triggering the soft-close dampener. To release the drawer, you lift the release lever (usually a blue or white tab) on the slide, which disengages the cone. The drawer bottom locking plate is a separate piece that snaps onto the drawer bottom and engages with a tab on the slide to prevent the drawer from tilting when extended. This plate is essential for stability.

Step-by-Step Installation

Follow these steps carefully. Always measure twice and drill once, and test the fit on a scrap piece if possible.

Mark the cabinet side: The slide must be mounted at a specific height. Typically, the slide’s bottom edge should be 18mm from the bottom of the cabinet opening (for a 16mm drawer bottom) or 20mm for 18mm. Use a square to draw a level line on both cabinet sides.
Attach the slide to the cabinet: Position the slide so its front edge is flush with the cabinet face frame (or recessed 1-2mm if using a frameless cabinet). Use the provided screws (usually 15mm long) to secure the slide through the pre-punched holes. Do not overtighten.
Drill drawer side holes: On the drawer box, measure from the front edge to the center of the locking device hole. This distance is typically 37mm from the front edge for most Tandem slides, but check the template. The hole is 10mm in diameter, drilled vertically into the bottom edge of the drawer side, at a depth of about 10mm. Also drill a 5mm pilot hole for the locking device screw (if your version uses a screw).
Install the locking device: Insert the locking device into the hole and secure it with the screw (if applicable). The cone should protrude outward.
Attach the drawer bottom locking plate: On the underside of the drawer bottom, near the front, center the plate and screw it in place. The plate’s tab should face the rear of the drawer.
Mount the drawer: Align the drawer’s locking devices with the slots on the slides. Push the drawer in until you hear a click. Then pull the drawer out to test.
Adjust: Use the adjustment screws on the slide: the front screw adjusts height, the rear screw adjusts side-to-side, and the slide’s base can be moved for depth. Make small adjustments and test again.

Common Problems and Solutions

Even careful installers run into issues. Here are frequent problems and how to fix them:

Drawer won’t close fully: The locking device may not be engaging. Check that the cone is aligned with the slot and that the drawer bottom locking plate is not obstructing the slide. Also, ensure the drawer box is square.
Drawer sags when extended: This usually means the drawer bottom locking plate is missing or not engaged. Verify it is snapped onto the slide’s tab.
Self-close is weak or absent: The dampener may be defective, or the slide is not level. Check the mounting height and that the slide is parallel to the cabinet bottom.
Drawer is crooked: Use the adjustment screws. Loosen the screws slightly, adjust, and retighten. If the drawer still sits crooked, the cabinet opening may be out of square.
Locking device pops out: The hole may be too deep. Remove the device and add a small shim (like a piece of tape) or fill the hole with wood glue and re-drill.

Comparison with Other Drawer Slides

Blum Tandem slides are often compared to side-mount slides and other undermount brands. Side-mount slides are cheaper and easier to install, but they are visible and typically have a lower weight capacity. Undermount slides like Tandem offer a cleaner look and better weight distribution. Compared to other undermount slides (e.g., Hettich or Accuride), Blum Tandem is known for its extensive adjustment range and the availability of accessories like tip-on (push-to-open) and servo-drive (electric opening). However, Blum Tandem requires precise drawer construction; the drawer bottom must be a specific thickness, and the drawer box must be perfectly square. Hettich’s similar system (e.g., Quadro) uses a different locking mechanism that some find easier to install, but Blum’s locking cone is very reliable once set.

Cost and Where to Buy

Blum Tandem slides are a premium product. A pair of 500mm slides typically costs between $20 and $35 USD, depending on the retailer and whether you buy in bulk. Locking devices cost about $2-4 each, and the drawer bottom locking plates are around $1-2 each. You can purchase them from specialty hardware stores, online retailers like Amazon or eBay, or directly from Blum distributors. Buying in bulk (e.g., 10 pairs) often reduces the per-unit cost. Be wary of extremely cheap knockoffs, as they may not meet Blum’s quality standards and may not fit genuine Blum accessories.

Safety and Accuracy Tips

Safety is important when using power tools. Always wear safety glasses and use a dust mask when drilling. When measuring, use a steel ruler for accuracy, and double-check all measurements before drilling. If you are installing slides in multiple cabinets, create a template from cardboard or thin plywood to speed up the process and ensure consistency. Also, be aware that the drawer box must be built with a 37mm front clearance (the distance from the front of the drawer side to the center of the locking device hole) – this is critical. If you are not confident in your ability to drill precise holes, consider using a drilling jig (available from Blum) or having a professional do the installation.

Frequently Asked Questions

Do I need a special drawer box for Blum Tandem slides? Yes, the drawer box must have a bottom that is at least 12mm thick, and the sides must be recessed to allow the slide to attach. The drawer sides should be flush with the bottom, and the front must have a 37mm setback for the locking device. You can use standard 16mm or 18mm plywood or MDF.

Can I install Blum Tandem slides on existing drawers? Possibly, but only if your drawer box meets the requirements. If your drawer has a thin bottom (e.g., 6mm), you will need to add a reinforcing panel. If the drawer sides are not recessed, you may need to modify them. It is often easier to build new drawers.

How do I adjust the soft-close tension? Blum Tandem slides have a fixed soft-close mechanism; you cannot adjust the tension. However, you can adjust the closing speed by using the optional “soft-close with adjustable damping” (available on some models like TANDEM plus). If your slides are too fast, check that the dampener is not worn out.

Why does my drawer stop short of closing? This is usually due to the locking device not being fully seated in the slide’s clip. Remove the drawer, check that the cone is clean and not damaged, and re-insert. Also, ensure the drawer bottom locking plate is not hitting the slide’s release lever.

Can I use Blum Tandem slides with a push-to-open mechanism? Yes, Blum offers a “TIP-ON” accessory that converts the slide to a push-to-open system, eliminating the need for handles. This requires a special TIP-ON adapter that replaces the standard locking device. You must purchase the TIP-ON kit specifically for Tandem slides.

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