A metal anchor expansion tool works by pulling back the screw of a hollow wall anchor to collapse the legs of the shell and secure it in the plasterboard of the stud wall. How this is achieved depends on the type of metal anchor expansion tool you are using.
While there are several types of metal anchor expansion tool, the only difference in the way they work is determined by whether they use a ratchet mechanism.
Function of non-ratchet type
Metal anchor expansion tools without a ratchet are only capable of fitting small, hollow wall anchors, intended for use on plasterboard of 12.5mm (½”) thickness or less. This is because they have a stroke length of less than 20mm (¾”) (see What metal anchor expansion tool sizes are available?). They can’t pull the screw of the hollow wall anchor back with repeated opening and closing of the handles so must fix the anchor with a single action of the handles being closed.
Once a hole has been drilled in the plasterboard and the hollow wall anchor inserted, the support surface and U-shaped pulling arm are placed between the screw head and flange of the hollow wall anchor.
When the handles are squeezed together, the U-shaped pulling arm is moved backwards, pulling the screw of the hollow wall anchor back. This causes the collapsing legs to fold back against the back of the plasterboard.
Function of ratchet type
Once a hole has been drilled in the plasterboard and the hollow wall anchor inserted, the support surface and U-shaped pulling arm are placed between the screw head and flange of the hollow wall anchor.
The two handles are then squeezed together to pull back the screw within the hollow wall anchor.
The ratchet mechanism keeps the pressure on the screw head as the handles are released, then as the handles are squeezed together again the U-shaped pulling arm and screw are pulled back further. This process is repeated until you feel a resistance caused by the collapsing legs having folded back against the back of the plasterboard.
How does the ratchet mechanism work?
The heads of some metal anchor expansion tools feature a linear ratchet mechanism that comprises three main parts: a pawl, a linear rack and a tension spring. As the handles of the tool are closed and brought together the linear rack is pulled back inside the tool’s head.
The teeth on the linear rack engage with the pawl which prevents the linear rack from moving forward again once the handles are released and opened. The tension spring maintains the contact between the linear rack and the pawl.
Each time the handles are closed together the linear rack gets pulled further back in the tool’s head, which in turn pulls the screw of the hollow wall anchor, folding back its collapsing legs until they meet the back of the plasterboard.
Once the hollow wall anchor has been set and you can’t close the handles any more, pressing the release button or lever disengages the pawl from the linear rack, releasing the tension and so making it easier to remove the tool from the hollow wall anchor and plasterboard.
