Elevator counterweight frame fabrication: fit and weld limits

A counterweight frame that measures inside tolerance on the bench can still bind on the guide rails halfway up the shaft. The frame is not a precision part. It is a locating bracket for 1,200 to 1,600 kg of filler plates, and its two controlling features are the guide shoe faces and the tie-rod holes. Elevator counterweight frame fabrication goes wrong when those faces are built from the outside of the frame instead of from the rail gauge, because a 3 mm error at the skin becomes a 3 mm error at the shoe and the shaft has nowhere to absorb it.

What follows is the sequence a design engineer should follow before releasing the drawing: what the frame carries, which dimensions decide installation, where welding moves the geometry, how the shaft environment changes the coating call, and what the first article should record. The same logic applies to a car sling. The sling has more brackets and a door interface, but the datum chain from rail centreline to mounting face is identical. The rest of the lift package is indexed in the elevator components hub.

What mass does a counterweight frame have to carry?

The counterweight balances the car plus roughly half the rated load, so the frame is sized by a weight stack rather than by bending load. For a 1,000 kg rated lift with an 800 kg car and a 50% balance factor, counterweight mass is 800 + 0.5 x 1,000 = 1,300 kg. At 25 kg per cast filler plate that is 52 plates. If the drawing shows a stack of 40 plates, the frame is 300 kg short of balance, and the machine runs with a higher current and a hotter brake coil for the life of the installation.

Two decisions follow from that number. Frame height is set by stack height plus tie-rod pitch, not by car height. And side-plate gauge is a weight decision before it is a strength decision: 2.0-2.5 mm CRCA is normally enough for the sides because the plates sit on tie rods and the base carries them vertically, while 4 mm sides add dead weight the machine accelerates on every trip and typically buy nothing.

The load path that matters runs from the rope or belt anchorage to the guide shoes. On most designs the termination sits on a head plate or on a separate anchorage bracket bolted to the frame head. Whoever owns that bracket should own its hole pattern too, ideally cut in the same operation as the head plate. A hand-drilled anchorage after coating is a routine source of a 2 mm offset that nobody notices until the ropes are tensioned and the frame hangs out of level.

Which dimensions decide whether the frame fits the shaft?

Rail gauge and guide shoe position decide fit, and everything else is secondary. Put the rail gauge, the rail head width and the running clearance on the drawing, then dimension the shoe mounting faces from the rail centreline datum rather than from the outer skin. A fabricator working to overall width can be inside plus or minus 0.5 mm on the skin and still put both shoes 1.5 mm out of position, because the skin includes bend allowance, plate thickness and the weld cap.

The second control is the tie-rod and filler-retention hole pattern, which sets the diagonal, and the diagonal is the cheapest check that the frame is square. On a 900 x 2,400 mm frame the diagonal measures 2,563 mm, and a 3 mm difference between the two diagonals corresponds to only 0.10 degrees of out-of-square. That sensitivity is useful, but it also means the reading must be repeatable: the same two corners, the same hook or laser reference, the frame at shop temperature, and no weld bead or burr under the tape.

The third control is bottom clearance and the buffer strike plate. The frame bottom must clear the pit floor across the whole travel with the buffer compressed, and the strike plate has to be square to the guide shoes rather than to the frame skin. If the design puts the strike plate on a bent flange, the brake's angular tolerance - typically plus or minus 0.5 to 1 degree depending on tool and gauge - can put a 250 mm flange 4 mm out of parallel. Face-mount the plate on a cut bracket, or tolerance the angle explicitly.

Tolerances and process limits for a counterweight frame

The values below are the ranges a lift OEM drawing normally calls for. The right-hand column is what the plant holds without a special agreement.

Why does the frame go out of square after welding?

Fillet welds shrink as they cool, and a frame welded on one side first pulls toward that side. On a 2,400 mm upright, two continuous 3 mm fillets on the same face will move the head by a millimetre or two and twist the shoe bracket further, because the bracket sits at the end of the longest lever in the assembly. The weld is sound and the frame is scrap, which is why weld distortion in frames is a sequence problem rather than a welding-parameter problem.

The countermeasure is restraint and order, not a smaller weld. Fix the uprights, head and base in a fixture that locates on the tie-rod bores, weld the two sides alternately in 150-200 mm backstep runs, keep the frame clamped until it reaches room temperature, and weld the shoe brackets last while they are still pinned to the fixture. A bracket welded after the frame leaves the fixture tells you nothing about the frame that will ship.

Cold straightening is acceptable on bare steel within the drawing's flatness call, but it leaves residual stress that reappears as a bowed upright after a season in a warm shaft. If the design needs a straightening allowance, say so and set the limit; a fabricator asked to make the frame straight will use whatever force it takes and charge for the result one way or another.

How should a counterweight frame be coated for a lift shaft?

A shaft is a mild corrosion environment with condensation, and a machine-room-less installation above a car park or inside an industrial building is worse. ISO 12944-2 classifies those as C3 medium and C4 high corrosivity, and the category belongs on the drawing because it decides whether one powder coat is sufficient or a zinc-rich primer is needed beneath it.

Ganesh runs a seven-tank pretreatment line, an electrostatic powder booth and a curing oven, then checks film thickness with a DFT gauge and adhesion with a cross-hatch test. Laser-cut edges take powder poorly when dross or oxide is left in place, so pretreatment has to remove it before the conversion coating forms. Edge condition is therefore a laser specification item as much as a paint item, which is why pretreatment and cutting are reviewed together on lift parts.

Masking is a drawing item, not a painter's judgement. Shoe running faces, tie-rod threads, earth studs and any face that receives a bolted joint should be paint-free. When the shaft is damp and the coating is the only barrier, a 15 micrometre shortfall on a masked edge is where the first rust bloom appears, usually inside the first year.

What should the first article inspection record?

Record the datum, not only the dimension. A first-article report for a counterweight frame should carry rail gauge, shoe-face position from the rail datum, tie-rod bore position, both diagonals before and after coating, overall height and width, weld size at the shoe bracket, DFT at three points and the cross-hatch result. PPAP and first article inspection are both available, and the report is worth more when the sample and the production frames come off the same fixture. Welded assembly tolerances sets out how to express those limits without over-constraining a weldment.

Record the filler stack as well: internal clear width at three heights. A frame can be square and still be 2 mm tight at mid-height because a weld pulled the side plate inward, and the plates then get hammered in on site. A fabricated checking fixture made in the in-house tool room, keyed to the filler plate width, catches that before dispatch.

What Ganesh runs for counterweight and car frames?

Ganesh has supplied counterweight frames, car frames and slings to TKE and Eros Elevators, alongside the guide rail brackets, fishplates, cabin panels, floor sills and controller enclosures that make up the rest of the lift package. Blanks arrive from a fibre laser or a 250 T punch, the 200 T five-axis brake forms them on a 4,450 mm bed, and welding happens in one of three CLOOS robotic MIG cells or at a manual station. Seven-tank pretreatment and powder coating follow, then assembly. Welding fixtures, checking fixtures and press tools come from the in-house tool room. The plants hold ISO 9001:2015 and ISO 14001:2015, and an effluent treatment plant is part of the manufacturing site.

The frame families are listed on the elevator sheet metal parts page, including the bracket and panel variants that ship with the same release.

What to put on the counterweight frame drawing?

1. Rail gauge, rail head width and running clearance, with shoe faces dimensioned from the rail centreline.
2. Balance factor, counterweight mass, filler plate size and pitch, and internal clear width at three heights.
3. Tie-rod bore diameter, position and hole-to-edge distance.
4. Weld size and finish at the shoe bracket, plus whether the frame ships as one weldment or in bolted sections.
5. Ownership of the rope or belt anchorage bracket, and who cuts its hole pattern.
6. Corrosivity category and coating system, with masking listed by feature.
7. Both diagonals, with the datum corners marked and the measurement method stated.
8. Annual quantity, release pattern, and whether the welded fixture is a one-off or a recurring tool.

The RFQ checklist covers the remaining drawing fields. For the welding detail on this part family, read welded elevator counterweight frames; for hole and edge limits on the sections, read laser-cut elevator frame sections.

When is a counterweight frame not a fabricated part?

Some designs use a cast iron counterweight or a solid block with no frame at all, and those are foundry items. Above roughly 6 mm of plate the frame competes with a structural weldment shop rather than a sheet metal line, and a hot-dip galvanised finish has to be arranged as a separate process if the shaft is unheated and coastal. Guide shoes, safety gear, rope terminations and buffers are bought-out components in every case.

Ganesh supplies the frame steelwork to the OEM drawing and does not certify the lift, the traction machine or the safety gear. CE marking under the EU lift directive or BIS conformity for an Indian installation stays with the lift OEM, which is also the party that signs off the shaft survey. If a drawing assumes the frame can be adjusted on site to correct rail gauge, the datum has already moved to the wrong place.