Flat Mending Plate 39x28mm Zinc Plated K4112a

The K4112a Flat Mending Plate In Sixteen Photographed Positions

Sixteen frames and not one bend. That is the whole point of the flat mending plate: a corner bracket wraps an angle, a plate lies flat across a joint that has no angle in it. The photographs show the same plate in rows, in pairs, at an angle, close enough to count the holes, and once with the figures printed on it. Between them they describe a part that is simple to the point of being easy to underestimate, and the reason it is worth a page of its own is that it fails where flat plates always fail: at the screw, in thin material, when the plate is asked to do a corner's job.

The plate is 1.0 mm zinc plated steel, rectangular, with four holes set in from the corners. On the annotated frame the plate measures 39 mm along its long edge and 28 mm across, with the holes pitched 15 mm apart across the width and 25 mm apart along the length. The plating is the yellow-green passivation that shows a rainbow where the light catches the edge of a hole, which is the finish most furniture plates are bought in because it protects the cut edges as well as the faces.

What A Flat Plate Does That A Bracket Cannot

A flat plate has no angle to match, so it does not care how square the joint is. That sounds like a small advantage and in practice it is the reason plates exist: a cabinet that has racked, a drawer bottom that has split along a groove, a table apron that has opened at a glue line, a flat pack panel whose cam fitting has torn out, all of these are joints where a bracket has nothing to grip and a plate has everything. The plate bridges the damage on the flat face, which is usually the only sound material left.

The second advantage is height. A plate lies within about a millimetre of the surface it is screwed to, so it fits where a bracket would foul: behind a drawer, under a shelf, inside a carcass against a back panel, in the gap between two panels that have to come together flush. On a repair job that gap is often the difference between a fix that is invisible and one that is not.

The Figures On The Frame

One frame carries the numbers: 39 mm along the long edge, 28 mm across the short edge, 15 mm between the holes across the width, 25 mm between them along the length, and 1.0 mm for the plate. Those five numbers are the whole of what the photographs state, and everything else a specification would want, the hole diameter, the edge distance, the flatness, the tolerance on the plate thickness, is a drawing matter rather than a photographic one.

The hole pitch matters more than the outline. Fifteen millimetres across and twenty-five along is a pitch chosen for a plate this size, and it decides what the plate can bridge: a split that runs between the two rows of holes will be pulled closed by the screws, and a split that runs under a row will be held but not closed. When a repair is being planned, offer the plate up dry and look at where the holes land before anything is driven, because a plate screwed into a split has made the split longer.

Screws, Thickness And What To Watch

On a 1.0 mm plate the screw choice does most of the work. The head needs to be wide enough to bear on the plate without dishing it, which means a pan or washer head rather than a small countersunk one. The shank needs to pass the hole without cutting a thread, because a hole that has been threaded will never hold the screw it was drilled for. And the length needs to bite into sound material without breaking the far face, which on furniture board is a narrow window and on a veneered panel is a decision about whether the repair will show on the other side.

Two habits keep plates in service. Pilot drill first, always, even in soft board: a plate that is screwed without a pilot will pull itself out of position as the screw bites. And drive in a cross pattern, one screw in each corner in turn, so the plate settles flat instead of cocking on the first screw and standing proud at the last.

Where The Plate Belongs

Edge joints are the classic use: two panels meeting edge to edge, a plate across the joint on the hidden face, four screws, joint held while the glue goes off. Splits are the second: a panel that has cracked along a groove or a fixing, bridged on the sound face, the crack pulled closed by the screw pair that straddles it. Failure repairs are the third and the most common in service: a cam fitting that has torn out of particleboard leaves a hole too big for any fitting, and a plate covers the hole and finds sound material around it, which is exactly what a repair plate is for.

There is a fourth use that is not a repair at all. A plate makes a joint that can be taken apart and put back, because the plate carries the load through screws rather than glue. Knock down furniture, exhibition stands and stage scenery all use flat plates for that reason: the joint comes apart with a screwdriver and goes back together square, which a glued or cam locked joint will not do twice.

Flat Plate Or Corner Bracket

The two parts are often stocked in the same drawer and used for the wrong jobs. A corner bracket holds two panels at ninety degrees and stops a corner opening; it needs a corner to sit in. A flat plate holds two surfaces in the same plane and stops a joint sliding apart; it needs flat material either side of the joint. Use a bracket where there is no corner and it stands off the face; use a plate where a corner needs holding and the joint will still open, because a plate cannot resist a change of angle.

Three Names For One Plate

Three names bring buyers to this part. Called by what it does, a mending plate. Called by its shape, a flat straight bracket. Called by the trade it serves, a furniture repair plate. All three describe the same rectangle of plated steel with four holes, and none of them states the size, which is why a plate order without dimensions is an order for whatever happens to be in the bin. Put 39 mm by 28 mm on the order and the ambiguity is gone.

Checks On Delivery

Four things to check on a carton of plates. Flatness: lay a plate on a surface plate or a sheet of glass and press one corner, a plate that rocks has been bent and will not sit down. Holes: run a finger inside each hole for a burr, which will stop a screw head seating and tear the plating. Edges: look for shear burr along the long edges, because a plate with a burr will not lie flat on a finished face without marking it. Finish: check the cut edges for bare steel, which is where a plating bath that was running weak shows first.

Then fit one dry. Offer the plate across a scrap joint, mark the holes, drill, and screw it down, then try to move the joint by hand. A plate that lets the joint slide has a pitch too wide for the material, and the answer is a second plate rather than a longer screw.

How A Plate Carries Load

A flat plate carries load in shear, not in bending, and that is why it is thin. The plate is screwed to sound material on both sides of a joint, and the screws transfer the load from one panel into the plate and out into the other panel. The plate itself only has to stay flat and stay put; the screws do the work. This is also why a plate with two holes on one side of a joint and two on the other is enough: the screw pair on each side is what resists rotation, and the plate is the bridge between them.

Understood that way, the failure modes of a plate make sense. A plate pulls out when the screws have nothing sound to bite, so the fix is to move the plate to thicker material or add a second plate across the joint rather than to fit a thicker plate. A plate lets a joint slide when its screws are too close to the joint line, so the fix is a longer plate that puts the screws further out. And a plate buckles when it is asked to hold a corner, because a plate has no stiffness out of its own plane, and nothing about the plate can change that.

Repair Sequence That Works

The sequence that succeeds on a failed joint is short and worth writing down. Clean the joint: old glue, splintered board and the remains of a torn out fitting all have to go, and a plate screwed over rubble is a plate that will be loose by the end of the week. Pull the joint together: clamp it, or screw a temporary batten across it, because a plate can hold a closed joint but cannot close one. Offer the plate dry and mark the holes where the material is sound, not where the plate looks centred. Drill pilots, then drive the screws in a cross pattern, and only then release the clamp.

The last step is the one that gets skipped. With the clamp off, load the joint by hand and watch the plate: any movement at the screw heads means the pilot was too large or the screw is too short, and the answer is a larger screw in the same hole rather than a second plate on top of the first. Two plates stacked on one joint look like a stronger repair and behave like a worse one, because the second plate is only as good as the first screw it shares.

Flat Plates And Finished Faces

A plate on a finished face leaves four screw heads and a bright rectangle, which is acceptable on the underside of a table and not acceptable on a wardrobe door. Three things make a plate less visible. Recess it: cut a shallow rebate the size of the plate so the plate sits flush with the face. Counter bore instead of countersink: a plate has no countersink of its own, and boring the holes for flat heads turns a plate that stands proud into one that disappears. Or put the plate on the hidden face and take the loss in reach, which is why a repair plate is usually fitted from the inside even when the damage is on the outside.

Packing And Counts

Plates are packed to count, and a stack of them should be checked for flatness at the top, the middle and the bottom, because a stack that has been compressed takes a set. Bag by size and label the bag: a 39 mm plate and a longer plate look similar in a bin and a mixed bag will be discovered at the bench. Count by hand for mixed orders, since plates of two sizes weigh close enough that a scale will not separate them.

Ordering The K4112a Plate

The K4112a is supplied as a flat mending plate in 1.0 mm zinc plated steel, 39 mm by 28 mm, four plain holes on a 15 mm and 25 mm pitch, packed to count. Hole diameter, edge distance and flatness tolerance follow the issued drawing.

Send the panel thickness, the joint you are trying to hold and the screw you intend to use, and the plate can be checked against all three before anything ships. If the joint is a corner rather than a flat seam, say so at enquiry: a plate is the wrong part for that job and a bracket is the right one.