Elevator floor sill manufacturing: forming, welding, finish

Elevator floor sill manufacturing turns on a single feature: a 5 mm groove that has to stay straight to 0.3 mm over 1,200 mm after two bends and a pair of welds, with the top face finishing within a millimetre of a floor screed that someone else is pouring.

The sill is the one lift part every passenger touches with a foot. It decides whether the door glides or grinds, and it is usually the first item on a snag list after handover. The drawing looks simple: a stainless channel with a groove down the middle.

The sill appears twice in a lift. The car sill travels with the car and carries the door on its track; the landing sill is fixed at each floor and closes the gap between the landing and the shaft. Both use the same profile, and both are made on the same route: cut, form, weld, finish. Elevator floor sill manufacturing is unforgiving because the tolerance stack runs the full length of the part rather than around a small feature.

What the door gib actually needs

The door leaf hangs from a track at the top and is held at the bottom by a gib that runs in the sill groove. The gib is a nylon or brass block, typically 4 mm thick, that keeps the door from swinging out of plane. Its clearance in the groove sets how much the door can rock.

A 5 mm groove with a 4 mm gib gives 0.5 mm each side. That is enough to absorb track misalignment and not enough for the door to rattle. Open the groove to 6 mm and the door gains 1 mm of play, which reads as a loose door in a quiet car. Close it to 4.5 mm and the first season of dust and grit turns the groove into a brake.

Two dimensions of the groove are critical, and neither is usually toleranced on a first drawing. Groove width must hold 5.0 ±0.2 mm over the full length. Groove edge straightness must hold 0.3 mm over 1,200 mm, measured along each side of the groove. The second one is what fails after welding, because a groove cut straight in a flat blank can close or open when the end caps are welded on.

The dimensional budget from floor to groove

The sill-to-floor relationship is the one dimension no factory can hold on its own. The drawing should carry a datum on the sill top face and a note that the installer sets it flush to the finished floor, because the factory dimension is the section, not the building.

How an elevator floor sill is manufactured from sheet

Cutting stainless without putting a scratch in it

Stainless sills are cut on the fibre laser with nitrogen assist, which gives a clean edge with no oxide on the cut face and no need for a grinding operation that would show on a No. 4 finish. The blank is handled on protective film from the moment it leaves the sheet, and it never slides face-down on a bare table.

The cut program leaves the groove as a pierced slot before forming, or cuts the blank for a stepped form, depending on the section. The second route is more common on a formed sill because a pierced slot plus a bend gives a groove with sharp internal corners and a burr at the base, which the gib wears against.

Two bends and a groove

A formed sill is usually three operations: form the nose return, form the back flange, then form the groove with a stepped punch that presses the strip between two shoulders. The order matters. If the groove is formed first, the part loses its flat reference for the nose bend, and the two features end up out of parallel by 0.3–0.5 mm.

Bending stainless needs a larger inside radius than mild steel to avoid cracking. A 1.5 mm SS 304 sheet at 350 MPa yield will crack at a bend radius below about 1.5 mm against the rolling direction; 1.2 mm sheet is more forgiving. The sill profile usually lands at 2–3 mm inside radius, which is safe and still tight enough for a 40–60 mm section height.

Springback on stainless runs 3–5° over a 90° bend, so the brake needs a compensated angle rather than an air bend at nominal. A sill that comes out at 87° will not sit flat on the landing and will read as a step at the nose.

Welding the ends without pulling the profile

The end caps close the section and give the sill something to bolt through. They are the only welds on a stainless sill, and they are short: 3–5 mm fillets at three edges, TIG, with a heat sink behind the joint.

A heat sink is not optional on 1.5 mm stainless. Without one, the end cap weld pulls 0.3 mm of bow into the last 100 mm of the sill, and the installer finds the ends rock on the landing plate. A copper or aluminium backing bar clamped behind the joint absorbs the heat and keeps the distortion inside the 0.3 mm straightness budget.

On MS sills the end caps are welded by MIG at 4 mm fillet, and the sill is straightened on a press after cooling. Straightening is a judgement call, not a specification — a sill that has been pressed back into line may carry residual stress that shows up as a bow after coating at 180–200 °C.

Finishing and protection

Stainless sills get no coating. They get a passivation after welding to restore the chromium oxide layer at the weld and the heat tint, then a No. 4 hairline finish applied in one direction along the length, then film.

The hairline direction is a specification detail that gets missed. A finish applied across the sill catches the light differently from one applied along it, and two sills from different batches in the same lift lobby will look mismatched. The drawing should state the grain direction and, for visible work, that all sills in a project come from one finishing batch.

MS sills go through the seven-tank pretreatment and powder booth, with DFT at 70–90 µm. The traffic edge — the nose and the groove shoulders — takes the most wear, and a thin coat there fails first. Masking the groove before coating is usually worth it, because powder build-up inside the groove reduces the width that the gib needs.

The car sill and the landing sill are not the same part

They share a profile and they do different jobs, and treating one drawing as the other is a common source of rework.

The car sill carries the door track load through the gib and takes the full weight of anyone stepping in. It is fixed to the car platform frame, usually with a return that drops over the platform edge, and its underside is visible from the shaft. The landing sill is fixed into the wall pocket at each floor, sits between two finished floor surfaces, and has to accommodate the landing door lock and the roller pick-up. Its ends are often cut at an angle to suit the wall thickness.

That difference shows up in the drawing fields. The car sill needs the platform frame fixing pitch and the door track position; the landing sill needs the wall pocket depth, the floor build-up and the lock cut-out. A single drawing issued for both will be right for one floor and wrong for every other.

The floor interface is where the tolerance is lost

The sill is set by the lift installer against a finished floor that is poured or tiled after the shaft is complete. The factory can hold the section to ±0.5 mm and still deliver a 3 mm step, because the floor moved.

Two details reduce the argument. First, put a machined or formed datum notch on the sill end that the installer can strike a line from, rather than relying on the top face, which is the surface being matched. Second, specify the acceptable step in the contract: ±1 mm is achievable with a screed that is set out from the sill; ±3 mm is what happens when the floor is laid first and the sill is packed to suit.

Where the floor is a raised access floor, the sill needs a deeper section to bridge the void and a support bracket at each end. That is a different part, not a packing detail.

Inspection before dispatch

The sill is a long, thin part, so inspection is about straightness more than size. Three checks cover it.

Lay the sill on a surface plate and measure the gap under the nose at the centre and at both ends. More than 0.5 mm and the sill will rock on a flat landing plate.

Run a plug gauge of 4.8 mm and a no-go gauge of 5.2 mm through the groove at five points along the length. A sill that passes at the ends and fails at the centre has a welding distortion problem, not a forming problem.

Check the squareness of the ends to the groove within 0.5 mm over the section height. An end that is 1 mm out of square pulls the sill sideways when it is bolted, and the door track no longer lines up with the groove.

For MS sills, add DFT at five points, a cross-hatch adhesion test on a coupon from the same batch, and a visual check that no powder has bridged the groove.

What Ganesh runs for lift entrance parts

Sills, door panels, car frames, counterweight frames and guide rail brackets are supplied to TKE and Eros Elevators from elevator parts. Stainless is cut on the 12 kW fibre laser, formed on the 200 T, 5-axis press brake with its 4,450 mm bed and Delem control, and the end caps are welded at the manual stations, with fixtures for the repeated lengths built in our own tool room. MS sills run the same cut-and-form route and then the seven-tank pretreatment line and the 18 ft × 14 ft powder booth, with DFT and cross-hatch checks recorded. The sheet metal RFQ checklist lists the fields an entrance-part enquiry needs, including the groove size, the finish direction and the fixing method.

Surface handling on stainless is covered in bending stainless steel without surface damage, and long-part straightness in bending long panels without distortion. The frame work that sits behind the sill is described in welded elevator counterweight frames. All lift component guides are collected under elevator and lift components.

What the lift drawing has to settle

1. Door opening width, sill overall length, and the wall pocket depth at each end.
2. Section profile with the groove width, depth, position from the nose and the straightness tolerance.
3. Material, grade, thickness and the surface finish, including grain direction.
4. End cap detail, fixing hole pattern and the datum they are positioned from.
5. Weld specification: which joints are welded, the process and the quality level.
6. Door clearance at the sill and whether a brush or rubber strip is fitted.
7. Coating specification for MS sills, with the groove masking requirement.
8. Packing and film, and whether the sills are delivered per floor or per lift.

When a formed sill is the wrong route

Below about 300 sills a year in one profile, extrusion is not worth a die and a formed sill is the right answer. Above that, an aluminium extrusion with a machined groove gives a more consistent groove and a lighter part, and a formed steel sill stops competing on cost. We form sheet; we do not extrude.

A formed sill is also the wrong answer for a curved or inclined entrance. A circular landing needs a curved sill with a varying section, which is a cast or a machined part, not a brake-formed one.

And where the sill has to be replaced in service without removing the door, the design needs a split or a slide-in detail that a one-piece formed sill cannot give. Say so on the drawing rather than discovering it during a modernisation.

Send the sill drawing with the door opening, groove detail and floor finish. Request a quote