Drilling a 35 mm Concealed Hinge Cup Hole: A Step-by-Step Guide
Drilling for a standard concealed hinge requires a 35 mm Forstner bit and an exact drilling depth typically between 11.5 mm and 13 mm to recess the hinge flush and cleanly into the cabinet door.
Fitting hinges to cabinet fronts requires utmost precision. A deviation of just a few millimetres when drilling can cause the door to bind, leave uneven gap reveals, or prevent it from mounting to the cabinet carcass altogether. Routing or drilling the cup hole is the most critical step when building furniture or replacing damaged fittings. This guide covers the entire process of preparation, drilling, and mounting with a focus on technical accuracy and proven workshop methods.
Technical Fundamentals: The C-Dimension and Cup Diameter
Before touching any tools, the exact positions on the cabinet door must be determined. The standard diameter for a regular concealed hinge is 35 mm. Smaller 26 mm variants are almost exclusively used for very light or narrow framed doors.
The most crucial parameter when positioning is the C-dimension (also known as the cup distance or edge distance). The C-dimension defines the distance between the outer edge of the cabinet door and the outer edge of the 35 mm hole. Depending on the hinge type, the required door gap, and the thickness of the cross mounting plate, this value typically varies between 3 mm and 7 mm.
To mark the centre point for drilling, use the following formula: Drilling centre point = C-dimension + 17.5 mm (half the cup diameter)
For example, if the manufacturer specifies a C-dimension of 4 mm, the centre point of the hole must be marked exactly 21.5 mm from the door edge.
Required Tools and Materials
The right setup is essential for clean drilling in chipboard, MDF, or solid wood. Blunt drill bits or working freehand will inevitably lead to tear-out or drilled-through door fronts.
- Forstner bit (35 mm diameter) with a centre point and scoring rims
- Pillar drill or powerful cordless drill driver (ideally used with a drill stand)
- Depth stop for the drill bit
- Try square or combination square
- Folding rule and sharp pencil (HB or H grade)
- Centre punch or a bradawl
- Wood drill bit (2 mm or 2.5 mm diameter) for pilot-drilling the fixing screws
- Matching concealed hinges / cabinet hinges
- Chipboard screws (typically 3.5 x 16 mm, PZ or TX drive)
Step-by-Step: Drilling the 35 mm Concealed Hinge Cup Hole
The following guide assumes a standard cabinet door (thickness 16 mm - 19 mm) fitted with 35 mm concealed hinges.
1. Define the Height Position of the Hinges
First, define the distance of the hinges from the top and bottom edges of the door. A proven standard in cabinetmaking is a distance of 100 mm to 120 mm from the respective edge to the centre of the hinge arm. For doors over 900 mm in height or with heavy weight (e.g. mirrored fronts), a third hinge must be positioned centrally between the two outer hinges. Mark these horizontal height lines on the inside of the door.
2. Mark the Drilling Centre Point (Apply the C-Dimension)
Measure inward from the side edge of the door (the hinge side) using your calculated measurement. If your C-dimension is 4 mm, mark a point exactly 21.5 mm from the edge along the previously drawn height line. Repeat this for all planned hinges.
3. Mark with a Centre Punch
Position the centre punch precisely on the marked crosshairs and tap it lightly with a hammer. This small indentation guides the centre point of the Forstner bit into position and prevents it from slipping on smooth melamine-faced boards when starting the drill.
4. Set the Depth Stop
The typical drilling depth for a 35 mm concealed hinge is between 11.5 mm and 13.0 mm. On a standard cabinet front with a 16 mm thickness, this leaves a minimal remaining thickness of around 3 mm to 4 mm. A precise depth stop serves as essential mechanical protection for your cabinet front. Adjust the stop on the drill stand or directly on the bit so that the cutters penetrate a maximum of 12.5 mm deep into the material.
5. Drill the Cup Hole
Clamp the door securely to your workbench. Place the Forstner bit into the punched indentation. Operate at a moderate speed (approx. 1000 - 1500 rpm) with steady pressure. Periodically withdraw the bit slightly to clear wood chips from the hole. Stop immediately once the depth stop contacts the timber. Vacuum the hole clean and check that the hinge cup sits completely flush.
6. Align and Secure the Hinge
Insert the hinge into the drilled cup hole. Place a square against the side door edge and align the hinge arm at an exact 90-degree angle to it. If the hinge is twisted, it cannot be clipped onto the mounting plate later. Mark the two fixing holes on either side of the cup. Pre-drill these with a 2 mm wood drill bit to a depth of around 10 mm. Secure the concealed hinge using the appropriate screws.
Choosing the Correct Hinge Crank / Overlay Type
The hole in the door is always identical, but the door position relative to the cabinet side is defined by the crank of the hinge arm. Choosing the right fitting depends on your cabinet construction.
- Full overlay (standard overlay): The cabinet door covers almost the entire cabinet side wall. The hinge arm is straight (0 mm crank). Full overlay concealed hinges are used here.
- Half overlay (twin overlay): Two doors share a single central cabinet divider. Each door covers only half the front edge of the partition (approx. 8 mm). The hinge arm is slightly cranked (usually 9.5 mm). Use half overlay concealed hinges for this setup.
- Inset: The door does not sit proud of the carcass but sits completely flush within the cabinet side walls. The hinge arm features a pronounced crank (usually 16 mm). Inset concealed hinges are used here.
In addition to the overlay type, the opening angle is an important factor. Standard doors usually utilise 110-degree concealed hinges / cabinet hinges. For corner cabinets or bespoke installations, angles such as 45 degrees, 90 degrees, or 165 degrees are required. For angled cabinets, 45-degree concealed hinges / cabinet hinges are typically used.
Furthermore, integrated damping has become standard across modern furniture fittings. Soft close concealed hinges / cabinet hinges cushion the momentum of the closing door and pull it shut silently over the final centimetres via an integrated hydraulic damper.
Mounting the Cross Plate to the Cabinet Carcass
Once the hinge is secured in the door, its counterpart—the mounting plate—must be fixed to the inside of the cabinet carcass. This generally follows System 32, the international cabinetmaking standard.
The front fixing hole for the mounting plate is standardly located 37 mm from the front edge of the cabinet. The distance between the two screw holes on the mounting plate is exactly 32 mm. The vertical position of these holes must match the height of the hinge arms on the door. It is ideal to use Euro screws (5 mm diameter) in pre-drilled 5 mm holes, as these provide significantly higher pull-out resistance in chipboard than standard wood screws.
Adjustment: Setting the 3D Door Reveals
A major benefit of concealed hinges is their three-dimensional adjustment capability after installation. If the door hangs unevenly or the reveals are misaligned, they can be corrected using three screws on the hinge arm:
- Depth adjustment: The rear screw on the hinge arm secures the position on the mounting plate. Loosening this screw allows the door to move roughly 2 mm to 3 mm forwards or backwards, adjusting the gap between the door and the front edge of the carcass.
- Side / Lateral adjustment: The front screw (often an eccentric cam screw) moves the door left or right. This aligns the lateral gap and ensures the door hangs parallel to the outer edge of the cabinet.
- Height adjustment: The cross mounting plate features slotted holes or its own cam screw. This allows the entire door to be raised or lowered by approximately 2 mm.
Common Mistakes During Hinge Installation
Tear-out around the cup hole This occurs if the Forstner bit is blunt or if too much pressure is applied at too low a rotational speed. On melamine-faced panels, the scoring spurs of the bit must cleanly cut through the hard decorative surface before the main cutting edge removes the core material.
Screws spinning loose in the chipboard If the fixing screws next to the cup are overtightened, the thread strips in the soft chipboard core. In this case, drill the hole out to 5 mm and insert a threaded wood insert or a plastic dowel. Alternatively, specialised hinge repair plates can be screwed over the damaged area to provide a solid base.
Door binds against the cabinet when opening If the door catches the carcass side when opening, either the wrong C-dimension was drilled or the side adjustment on the hinge arm is set too tight. An incorrect mounting plate thickness can also cause this issue. Check the manufacturer technical data to confirm which mounting plate spacing (typically 0 mm, 1.5 mm, or 3 mm) is required for your selected C-dimension.
FAQ – Frequently Asked Questions About Concealed Hinge Drilling
Which drill bit is required for a standard concealed hinge? A 35 mm Forstner bit or machine drill bit is strictly required. Standard twist drill bits do not exist in this size for handheld use and cannot produce a flat-bottomed hole.
How deep does a 35 mm hinge cup hole need to be? The standard depth is between 11.5 mm and 13.0 mm. The hinge cup must sit completely flat inside the recess. The exact depth depends on the specific hinge model and manufacturer.
Can I enlarge a 26 mm cup hole to 35 mm? This is nearly impossible to do freehand because the 35 mm Forstner bit lacks a centre point to guide its tip, causing it to run off course. The solution is to glue a matching wooden plug flush into the 26 mm hole and re-drill the 35 mm hole once the glue has fully cured.
What does "soft-close" mean for cabinet hinges? Soft-close refers to an integrated damping mechanism. A small hydraulic cylinder inside the hinge cup or arm slows down the closing motion from an angle of roughly 30 degrees and pulls the door shut smoothly and silently.
How many hinges do I need per door? As a general rule: for doors up to 900 mm in height and 4 kg to 6 kg in weight, 2 hinges are sufficient. Up to 1600 mm and 12 kg to 17 kg, 3 hinges are required. Heavy tall cabinet doors up to 2000 mm should be fitted with 4 to 5 hinges to prevent the door front from warping.