Fitting a Flap Stay — Wall Cabinet Flap

A flap stay secures the open position of a cabinet flap and controls its movement during opening and closing.

Whether in the kitchen, bathroom or living room: wall cabinets with horizontally opening flaps require precisely guided kinematics. The mechanical load on the fittings and the carcass is substantial. A correctly dimensioned and fitted fitting prevents the front from dropping uncontrollably, protects the material from damage and ensures ergonomic operation. Much like a car's gas strut holding up the bonnet, the fitting takes the weight of the furniture front and cushions the end positions.

This guide is aimed at fitters and ambitious DIY enthusiasts who want to install a new flap stay or replace a faulty one. The focus is on correctly determining the installation dimensions, selecting the appropriate force in Newton, and ensuring precise fitting.

Initial Considerations: System and Force Selection

Before reaching for the drill, the appropriate system for your specific furniture front must be selected. The choice of fitting depends largely on the direction of movement (flap opening upwards or downwards) as well as the weight and dimensions of the front.

Mechanical vs. Gas Strut

In principle, a distinction is made between purely mechanical stays and pneumatic systems. A mechanical stay often operates using adjustable friction, a spring, or a cable pull. These systems frequently allow the flap to be stopped smoothly at any desired opening angle (multi-position stop).

A Gas Strut, on the other hand, utilises compressed gas within a cylinder. It pushes the flap open automatically beyond a certain angle and holds it in the maximum end position (usually 90° or 110°). For fronts with high intrinsic weight, such as solid wood or thick MDF, one typically relies on Gas Struts for Heavy Flaps, as these deliver high holding forces within a compact footprint.

Calculating the Correct Force

The holding force is specified in Newton (N). A common mistake during fitting is selecting an incorrectly sized stay. If it is too weak, the flap will fall down. If it is too strong, closing the flap requires considerable effort, which can tear the hinges out of the carcass over time.

To find the matching Flap Stay, you need to determine the weight of the front including the handle. As a rule of thumb: 10 N corresponds to a holding force of approximately 1 kg. A typical chipboard (19 mm thick) weighs around 13 kg per square metre. For a flap measuring 600 mm x 400 mm, this results in an area of 0.24 m². The weight of the bare panel is therefore roughly 3.1 kg. Adding a solid metal handle of 0.4 kg brings the front weight to 3.5 kg. In this scenario, a stay with 50 N or 60 N would be the right choice. From a carcass width of 600 mm upwards, it is strictly recommended to install two fittings (left and right) to prevent the front from warping. In this case, divide the total required force by two.

Fitting Preparation

For a professional installation, you will require the following tools and materials:

Tools Required

• Cordless drill/driver with torque control
• Wood drill bit (Ø 2 mm or 3 mm)
• Screwdriver or matching bit (usually Pozidriv PZ or Torx TX)
• Tape measure or folding rule
• Set square
• Pencil or bradawl

Materials

• The matching Flap Fittings (stay, brackets for carcass and front)
• Wood screws (countersunk, typically 3.5 x 15 mm or 4 x 16 mm)
• Separate hinges if required (a flap fitting does not usually replace the top concealed cup hinge that holds the flap to the carcass)

Time required: Allow approximately 20 to 30 minutes per cabinet flap for measuring and fitting.

Step-by-Step Guide: Fitting a Flap Stay

The following steps outline the classic installation of a gas strut for an upward-opening flap. For mechanical cable-pull systems or braking stays for downward-opening bar compartments, the specific mounting dimensions differ – consult the manufacturer's enclosed data sheet for these.

Step 1: Marking Mounting Dimensions on the Carcass

The correct positioning of the mounting brackets determines the subsequent opening angle of the flap. Decide whether the flap should open at a 90° angle or further (e.g. 110°).

Measure downwards from the top inner edge of the carcass. For an opening angle of 90°, the drilling dimension for the carcass bracket is often around 250 mm - 270 mm (depending on cylinder length). Next, measure backwards from the front inner carcass edge (usually 15 mm - 20 mm). Mark this intersection point precisely with a bradawl.

Step 2: Marking Mounting Dimensions on the Front

Now mark the position on the inside of the flap. Measure downwards from the edge where the hinges sit (top edge of the flap). This measurement is typically 90 mm - 100 mm. The distance to the lateral outer edge of the flap must correspond exactly with the position of the carcass bracket, ensuring the stay runs parallel to the side panel without binding.

Step 3: Pre-drilling

To avoid chipping the melamine coating or splitting the MDF, all marked points should be pilot-drilled. Use a wood drill bit with a 2 mm or 3 mm diameter. Drill no deeper than 10 mm. If necessary, use a depth stop on the drill to avoid accidentally piercing through the front.

Step 4: Mounting the Fixing Brackets

Now screw on the round or oval fixing plates. Start on the carcass side. Ensure that the pin onto which the strut will later be clipped faces the correct direction (usually inwards towards the cabinet interior according to manufacturer drawings). Next, fix the bracket to the front. Use your cordless driver on a low torque setting to avoid stripping the screws in the chipboard.

Step 5: Inserting the Stay

Fitting the cylinder itself is generally tool-free. Push the head of the strut onto the ball stud of the fitted carcass bracket until it audibly clicks into place. Pay attention to orientation: the thick cylinder section is typically attached to the carcass, with the thinner piston rod fitted to the front. Repeat the process on the front bracket.

Visual tip: For open shelving or glass fronts, the aesthetic of the hardware matters. Coordinate the cylinder colour with the furniture design. A Gas Strut in Silver matches modern, technical kitchens, whilst a Gas Strut in Black looks discreet against dark wood decors. For white carcasses, a Gas Strut in White is ideal.

Step 6: Functional Check and Adjustment

Open and close the flap several times. Movement should be smooth. The flap must open effortlessly, swing up automatically in the upper range, and hold securely in its end position. When closing, the flap must not slam down unchecked. For mechanical friction systems, you can now adjust the friction via an adjustment screw on the joint so that the front remains stationary at any desired angle. Gas struts cannot have their force adjusted retrospectively.

Common Installation Mistakes

• Incorrect kinematics due to measuring errors: If the drilling dimensions deviate by even a few millimetres from the data sheet, the opening angle changes drastically. The flap will either fail to open wide enough, or the strut will prevent the front from closing completely.
• Forgetting the hinges: A flap stay guides movement and carries weight, but it does not replace the top hinge. Without a suitable concealed cup hinge (ideally without an integrated self-closing mechanism, which could work against the strut), a flap cannot be installed.
• Single-sided fitting on wide fronts: Fitting only one stay on a front width exceeding 600 mm causes the material to twist upon closing. The front will no longer sit flush against the carcass on one side.

FAQ – Frequently Asked Questions

Can I use a standard stay for a downward-opening flap? No. For bar cabinets or bureau flaps opening downwards, you require dedicated drop-flap stays. These feature inverse kinematics: they brake the descent of the front and hold it horizontally (often at a 90° angle) to relieve strain on the bottom hinges. A standard overhead wall-cabinet strut would continuously force the flap downwards.

How do I release a clipped strut for removal? Most ball joints feature a small metal spring clip at the strut head. Slide a flat-head screwdriver underneath this clip and pry it upwards gently. This expands the retaining mechanism, allowing the cylinder to be pulled off the ball stud.

My flap slams shut loudly even though the strut is new. Why is this? A gas strut is primarily engineered to push the flap upwards and keep it open. It is not a dedicated soft-close furniture damper for the closing stroke. If the flap slams shut, you will need either hinges with integrated soft-close damping or separate buffer stops (rubber pads or drill-in door dampers) inserted into the front carcass edge.

What does the stroke mean on a stay? The stroke describes the travel distance in millimetres that the piston rod can extend out of the cylinder. It therefore defines the operating range of the fitting. A longer stroke is required for taller overhead cabinets to achieve the necessary opening angle.