When the original drawing of a slewing bearing is lost, a replacement can still be manufactured from careful measurements of the worn ring. Outer diameter, bore, ring height, bolt hole pattern, and gear data (if the ring has teeth) are normally enough for a manufacturer to reverse-match the geometry, issue a drawing for approval, and machine a dimensionally matched replacement. The practical question in this situation is not "which catalogue part fits" but "which supplier can reverse-match the geometry from the worn ring, issue a drawing for approval, and then keep producing that ring whenever the machine - or another machine of the same model - needs one".

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1. A missing drawing is not a dead end: a slewing ring is a geometric part, so a worn one can be measured on the bench or in the machine and reproduced from those dimensions - no proprietary design data required.

2. Six measurements carry most of the information: outer diameter, bore, ring height, bolt hole count and hole diameter, bolt circle diameter (PCD), and gear parameters if the ring is toothed.

3. Photos are part of the specification: mounting surfaces, wear marks, seals, and any legible nameplate or part number help a supplier confirm the geometry and spot damage that measurement alone will not show.

4. The first ring becomes the reference for the rest: once a replacement ring is approved and running, the same measured geometry covers every other machine of that model - so one measurement job supports the first ring and every ring ordered after it.

5. Verify metrology before you pay a deposit: in-house coordinate measuring machine inspection and a live video walkthrough of the production line are the two simplest ways to check that a no-drawing order will fit when it arrives.

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It comes up more often than most buyers expect. Machine tools, cranes, excavators, and rotary tables stay in service for 10, 15, sometimes more than 20 years. The slewing bearing that supports a rotary table, a slewing platform, or a turntable develops play, noise, or excess backlash - and by then the paperwork is gone. It was never handed over with the machine, the machine has changed owners two or three times, or the original equipment manufacturer no longer supports that model.

For a maintenance team this looks like a dead end: the machine is mechanically sound, the drive still works, the structure is fine - and the only thing standing between the plant and a working machine is one component nobody has documentation for. Waiting for an obsolete OEM spare can take months, if it is available at all.

What usually breaks the deadlock is measuring the worn part. A slewing bearing - even a fully customised one - is a geometric component: its function depends on matching dimensions, not on proprietary design knowledge. Measure it accurately and the geometry can be reproduced, which is how most excavator swing bearing repair and machine tool replacement jobs are actually solved in practice.

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The list is shorter than most buyers expect. A tape measure, calipers, a depth gauge, and a phone camera usually cover it. Laser or coordinate measurement is welcome, but it is rarely required at the quotation stage.

The measurement set that matters: OD, bore, section heights, bolt hole count and diameter, bolt circle diameter (PCD), chord length, and gear data. Sketch it on paper if that is faster - suppliers who do this work regularly read field notes every week.

You do not need to produce a formal drawing of your own. Send the numbers with clear photos and say which values are rough and which are exact. If the machine make and model are known - for example a widely used hydraulic excavator or a standard vertical machining centre - include the model and the position of the ring as well: in many cases the original part number can be identified from that, which shortens the whole process considerably.

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Once outer diameter, bore, height, bolt pattern, and gear data are confirmed, a manufacturer can work in three steps:

This is closer to reverse-matching an existing geometry than to designing something new. The critical dimensions are already fixed by the machine: the replacement has to seat on the same mounting face and pick up the same bolt circle as the ring it replaces. A drawing would document that geometry - measuring simply recovers it.

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Replacement work starts with one worn ring, but it rarely ends there. Once a measurement-based ring has been manufactured and approved, that drawing becomes the reference for the part: the next time the same machine needs a ring - or another machine of the same model on site needs one - production runs against a geometry that is already confirmed, instead of measuring from scratch again.

That is worth planning rather than reacting to. If several machines of the same model are in service, the measurement and approval work is paid for once and then spread across every ring ordered after it. Batch quantities also give a workshop more room to schedule production properly - material, heat treatment, and grinding planned as a run rather than squeezed in around a breakdown.

Planning tip: before you place the order, check how many machines of that model are running on site and how many are due for a bearing change. A planned set of rings against one approved drawing is generally a better position to negotiate from than an emergency ring ordered while the machine is already down.

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Because there is no original drawing to fall back on, it is reasonable to want evidence before paying a deposit on a part of this size and cost. Two questions are worth asking any supplier that offers a measurement-based replacement:

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Having this ready before the first inquiry normally compresses several rounds of back-and-forth into one - which is the difference between "the machine is down" and a quotation you can act on.

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At Anhui Yuanfeng Slewing Rings Co., Ltd. we machine, heat treat, grind, and assemble slewing rings in-house in Hefei, China. Our standard range covers diameters from 200 mm to 6,000 mm in single-row four-point contact ball, double-row ball, crossed roller, and three-row roller designs, with internal or external gearing as specified.

Rings are produced from 42CrMo and 50Mn steel, raceways are induction hardened to HRC 55-62, and every unit is measured on a Zeiss CMM with a unique product ID for full traceability. Our minimum order is 1 piece, so a first replacement ring for a machine whose drawing no longer exists is a practical starting point, and standard custom production takes about 40 days. Repeat and batch orders - the same ring for other machines, or a scheduled set for a fleet - are produced against the drawing that has already been approved, which shortens the work on every ring after the first.

If you send your measurements and photos, our engineers will check feasibility, tell you honestly whether the measured geometry can be reproduced, and issue a drawing for your approval before any material is cut. Replacement and custom rings are used in cranes, excavators, machine tool rotary tables, and other special machinery, in gearless, internally toothed, and externally toothed versions.

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Replacing a slewing bearing when the original drawing is gone

Q: Can a replacement slewing bearing be made with no drawing at all?

Yes. The replacement is reverse-matched from measurements of the worn ring: outer diameter, bore, height, bolt hole pattern, and gear data if the ring is toothed. We issue a dimensioned drawing for your approval and manufacture to it. Our minimum order is 1 piece so a first ring is practical, standard production is about 40 days, and further rings for the same model are produced against the same approved drawing.

Q: What if the ring cannot be removed from the machine to measure it?

In most cases the outer diameter, seat, and bolt circle are still reachable on the machine. Measure what is accessible, photograph the rest, and mark which values are approximate - feasibility can still be assessed. A more precise measurement can then be planned for a scheduled downtime window.

Q: How accurate do my measurements need to be?

Measure as carefully as your tools allow and state which figures are rough and which are exact. The first quotation is based on those numbers. The dimensions that decide fit - bolt circle, bore, heights, and gear data - are confirmed on the approval drawing before production starts, so a small error caught at that stage costs nothing.

Q: Can a replacement ring include the original gear teeth?

Yes. Rings can be supplied gearless, internally toothed, or externally toothed. For a geared replacement, send the module, tooth count, pressure angle, and tooth height measured on the worn ring, plus photos of the mating pinion and any visible wear on the teeth.

Q: Why not simply order the part number from the original manufacturer?

Often it is no longer supplied: the model is obsolete, the brand has changed hands, or the spare is only available inside a larger assembly with a lead time measured in months. A measurement-based replacement ring, produced in about 40 days against dimensions you can verify beforehand, is frequently the faster route back to production.

Q: What does a replacement slewing ring cost - and does quantity change it?

Cost depends on diameter, design type (ball, crossed roller, or three-row roller), whether the ring is geared, the accuracy required, and the quantity. The measurement and drawing work is done once, so unit cost improves as the order moves from a first ring to a repeat or batch quantity. Send the measured dimensions, photos, and the machine model - it also helps to say how many machines of that model you run - and our engineers will reply within 24 hours.

Replacing a worn slewing ring on a machine with no paperwork? Leave a message with your measurements and photos - our engineers reply within 24 hours.