Measuring a door lock gearbox is essential for finding a suitable replacement or identifying the correct part for repair. The 'size' of a door lock gearbox typically refers to specific measurements that determine its compatibility with the door and other lock components like handles and cylinders.
Key Measurements for Door Lock Gearboxes
To accurately measure a door lock gearbox, you need to take several specific dimensions. These measurements ensure the new gearbox aligns correctly with the door cutouts, the handle spindle, and the locking cylinder.
Here are the critical measurements, incorporating the details from the provided references:
STEP 1: FIRST MEASUREMENTS
- A - Handle/Spindle Centre (PZ Size): This is the distance from the centre of the keyhole (or cylinder) to the centre of the handle/spindle. This measurement is often referred to as the "PZ" size and is a fundamental dimension for compatibility.
STEP 2: MORE MEASUREMENTS
- F - Faceplate Width: This measurement is the horizontal width of the faceplate that sits flush to the edge of the door.
Additional Common Measurements
While the provided references focus on the PZ size and faceplate width, other measurements are standard when identifying a door lock gearbox:
- Backset: The distance from the leading edge of the faceplate to the centre of the handle spindle or the centre of the keyhole/cylinder. This is a very important measurement, alongside the PZ.
- Overall Length: The total length of the faceplate from top to bottom.
- Screw Centres: The distance between the screw holes on the faceplate or within the gearbox body used for fixing it to the door.
- Case Height and Depth: The dimensions of the main gearbox body that fits inside the door pocket.
Why Accurate Measurements Matter
Getting these measurements right is crucial because door gearboxes are not universally sized. Different manufacturers and types of locks (like UPVC door locks, multipoint locks, sashlocks, etc.) use varying dimensions. Using the correct measurements ensures:
- The handle spindle aligns with the gearbox.
- The lock cylinder aligns with the keyhole centre.
- The faceplate fits correctly on the door edge.
- The gearbox body fits within the routed pocket in the door.
How to Take the Measurements
Here's a simple guide:
- Remove the Gearbox: If possible, remove the gearbox from the door. This makes measuring much easier and more accurate. Unscrew the faceplate and slide the gearbox out of the door's edge.
- Measure PZ Size: Use a ruler or tape measure. Place the zero point at the centre of the handle spindle square and measure straight down to the centre of the circular part of the cylinder hole.
- Measure Backset: Measure from the edge of the faceplate (the part that touches the door edge) to the centre of the handle spindle or cylinder hole.
- Measure Faceplate Width: Measure the horizontal width of the metal strip (the faceplate).
- Measure Other Dimensions: Measure overall faceplate length, screw hole distances, and the height and depth of the main gearbox case as needed.
Example Measurements
Let's consider a common scenario for a UPVC door lock gearbox:
- PZ Size: 92mm (The distance from the handle spindle centre to the cylinder centre).
- Backset: 35mm or 45mm (Distance from the faceplate edge to the spindle/cylinder centre).
- Faceplate Width: 16mm or 20mm.
Finding a gearbox with these exact measurements (PZ, backset, and faceplate width being the most critical) is usually necessary for a direct replacement.
