Buyers often say “mill me a gear.” On a real shop floor that can mean three different processes. Knowing the difference helps you specify the right process, compare quotes fairly, and avoid soft accuracy promises. Anand Gears runs hobbing and thread milling for product and for gear cutting job work — this article stays process-focused, not capacity-sheet focused.
Gear hobbing (generating process)
A hob is a cutter that looks like a worm with gashes for cutting edges. The hob and blank rotate in a timed ratio while the hob feeds across the face. The involute (or worm-wheel profile) is generated by the relative motion, not stamped by a single tooth-shaped tool.
- Common for spur, helical, and worm wheels in industrial production.
- Strong for repeat batches once the setup (index, lead, depth) is proven.
- Accuracy depends on machine condition, hob quality, blank prep, and fixturing — not on magic numbers printed in marketing.
Form milling (tooth-by-tooth milling)
Form milling uses a cutter ground to the tooth space shape. The blank is indexed after each space. It is flexible for one-offs and odd tooth counts when a suitable hob is not on the shelf, but cycle time rises with tooth count and indexing errors can accumulate if the index setup is weak.
- Useful for prototypes, repair gears, and non-standard profiles.
- Less ideal as the default for large production runs of standard spur/helical teeth.
- Surface finish and spacing quality track operator and machine care closely.
Thread milling for worms
Industrial worm shafts are usually not hobbed the way a spur gear is. They are thread-milled (and sometimes ground after heat treatment on high-duty work). Lead, multi-start geometry, and journal steps are controlled on a thread-milling setup. The mating worm wheel is then hobbed with a hob compatible with that worm geometry. That is why a matched worm set from one shop is easier to trust than a worm from vendor A and a wheel from vendor B.
Accuracy and batch-size implications
- One-off / repair — form milling or reverse-engineered hobbing from sample; expect setup time to dominate the quote.
- Small pilot batch — hobbing if a hob exists; worth investing setup for consistency across the batch.
- Repeat production — hobbing (wheels/spur/helical) + thread milling (worms) with fixed process sheets and first-article checks.
Hardening, grinding, and shaving are separate finishing paths used when duty demands them — ask whether the quote is “cut only” or “cut + heat treat + finish.”
What buyers should ask a job-work vendor
- Which process will you use — hobbing, form milling, or thread milling?
- Do you work from drawing, sample, or both? (Dimensions in mm.)
- How will first-article inspection be reported (tooth count, OD, span/MOP if applicable, journal sizes)?
- Is heat treatment included? Who owns grinding if required?
- For worm sets: will worm and wheel ship as a matched pair?
- Can you also machine the housing/flange, or is this teeth-only?
How Anand Gears fits
Our shop combines gear hobbing, worm thread milling, CNC turning, and HMC/VMC housing work under one roof. That stack is what OEM job work and complete gearboxes both use. Send drawings or samples via the job work page or contact.
Related: Gear Cutting Job Work · Worm Gear Sets & Spares · Contact