Process Deep-Dive · Reverse-Engineered Reproduction
Recasting a broken elevator cable reel
A spoked cast-iron cable reel cracked at the hub and took an elevator out of service. With no spare and no drawing, we reverse-engineered the wheel from the broken original and poured a replacement in gray iron.
The process, step by step
From a cracked spoke to a running elevator
The reel failed where a spoke meets the hub — a classic gray-iron fracture. We used the broken wheel itself as the design source, rebuilt it in CAD, and poured a replacement from a printed sand mold.
The failure: a cracked spoke
The reel came in broken at the hub. Gray iron is strong but brittle — it fails catastrophically rather than bending. With no spare and no drawing, the broken wheel itself becomes the design source.
Read the part
We measure and digitize the wheel — the spiral cable groove, the six spokes, the hub bore — capturing the geometry that has to be reproduced exactly to fit the existing machine.
Rebuild the raw casting in CAD
The reel and its mold package — cope, drag and core — are modeled in 3D with draft and gating added for a wheel this size. Trimming weight wouldn’t save much here: on a large part it’s the mold size, not the metal, that carries the cost.
Print the mold & set the core
The drag is printed in resin-bonded sand with the central core that forms the hub bore. No pattern to cut — the printed mold comes straight off the model.
Close & pour
The mold is assembled, dried, and poured with induction-melted gray iron at verified carbon and silicon chemistry.
Shake out
The reel breaks out of the sand still dark with adhered burnt binder and gating attached — the deep helical cable groove and six-spoke hub already crisp.
The replacement reel
A raw gray-iron casting, ready to clean up and finish-machine the bore — a drop-in replacement cast from a part that arrived in pieces.
Material
Gray iron, to ASTM A48
This reel is gray iron, Class 30 — the right balance of strength and machinability for a sheave that carries cable in compression. We pour the full A48 class range, certified to the same chemistry tolerances we hold for industrial production.
| Grade | Min. tensile (psi) | Hardness (HB) | Typical use |
|---|---|---|---|
| Class 20 | 20,000 | 141 (max) | Intricate, low-stress castings |
| Class 25 | 25,000 | 174 | General-purpose work |
| Class 30 | 30,000 | 201 | Sheaves, wheels, housings — this reel |
| Class 35 | 35,000 | 212 | Higher-strength service |
| Class 40 | 40,000 | 235 | Heavy-duty, wear-resistant |
Gray iron fails catastrophically rather than bending, so it is never used structurally to hold a landing and steps — but a reel loaded in compression is an ideal use. Where steel-like ductility is needed we pour ductile iron to ASTM A536 instead.
Reproducing a machinery part from a broken original
- The broken part is the pattern — a complete original — even in pieces — carries every dimension we need; no drawing required.
- Mold size drives cost — on a large wheel, removing metal barely helps — the big mold carries the processing cost.
- Add draft & round the corners — vertical faces get draft to draw clean; sharp reliefs are broken to kill hot spots.
- Allow 1% shrink — the casting comes out ~1% smaller than the pattern — sized in at the model stage.
- Machine the fits last — the hub bore and any mating faces are cast close, then finish-machined to the existing shaft.
- Gating & risering are ours — we feed the heavy hub and rim sections so they solidify sound.
Figures
The full sequence