Part types / Large flanges, rings and slew bearings
Machining for Large Flanges, Rings and Slew Bearings
Diameter greater than length, and usually heavier than it looks on the drawing.
A ring, flange or bearing race is defined more by its diameter than by its length, which is what points the work at a vertical turning lathe rather than a horizontal one. The part sits on a rotating table with its own weight going straight down into the table rather than sideways into a chuck, which is why these machines can turn parts that would overload a comparable horizontal lathe.
Bolt circles, sealing faces and mating flatness usually matter more than the raw diameter tolerance. A flange that is round to the drawing but not flat where a gasket sits, or whose bolt holes do not line up with the mating part, fails on assembly even though every individual dimension checked out.
What decides the tolerance
The features that carry most of the risk on this part type, before you get to the machine that cuts it.
- Flatness on sealing facesWhere a gasket or O-ring seals, usually toleranced tighter than the rest of the part.
- Bolt circle positionHole pattern diameter and spacing that has to match a mating flange from a different supplier.
- Concentricity to a bore or spigotA register diameter that centres the part against its mate before the bolts are even tightened.
- Raceway geometry on slew bearingsBall or roller path form and hardness, usually specified by the bearing designer rather than left to the machinist.
- Table load, not chuck loadThe deciding factor for whether the part suits a vertical lathe, since weight goes down into the table rather than sideways.
Where this work usually goes
Typical envelopes and table loads for each machine class are on the machine class reference.
Vertical turning lathe
The default route once diameter clearly exceeds length, often with a live milling head fitted to add bolt holes without a second setup.
Horizontal boring mill
Where a ring is part of a larger fabrication and cannot be chucked as a standalone turned part.
Materials
Forged alloy steel for highly loaded rings and slew bearing races, cast steel or ductile iron for lower duty flanges and housings, and stainless grades where the flange is in a sealing or hygienic service.
Before you send the RFQ
- State finished weight and diameter together. Table capacity is rated in both, and one without the other is not enough to place the work.
- Give the bolt circle diameter and hole count against a named standard where one applies, not just a drawing dimension.
- Flag which face is the sealing face, since that is usually where the tightest flatness callout belongs.
- For a slew bearing race, confirm whether raceway hardening and grinding are in scope or handled by a separate specialist.
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