No Original Girth Gear Drawing? What You Need to Order a Replacement

The mill is still running, but its girth gear is worn. Your maintenance team has photographs, a few old inspection reports, and perhaps a drawing that shows the gear in the assembly. What you do not have is a complete manufacturing drawing.

This is a familiar situation in older cement and mining plants. Equipment changes owners, documents go missing, and the original supplier may no longer support the machine. It does not necessarily mean a replacement girth gear is impossible to make. It does mean that someone must establish and verify the missing information before production starts.

A replacement can sometimes be developed from an existing gear, a segment, the mating pinion, and field measurements. But a photograph or outside diameter alone is not enough to release a manufacturing drawing.

This article explains what to collect, what needs to be measured at site, and where buyers should insist on a technical review rather than accept an early assumption.

Yile Machinery manufactures custom girth gears and pinions for mills, rotary kilns, and other heavy equipment. If your documentation is incomplete, we can review the information you have and identify what else is needed to assess a replacement project.

Can a Girth Gear Be Made Without the OEM Drawing?

Often, yes—but “without the OEM drawing” does not mean “without a verified drawing.”

Before manufacturing, the supplier and buyer still need an agreed technical basis covering:

• Tooth geometry

• Gear body and segment construction

• Mounting dimensions

• Material and heat treatment

• Inspection requirements

• Compatibility with the existing pinion

The missing OEM drawing may be replaced by a new drawing prepared from measured and confirmed information. Until the critical dimensions have been checked and that drawing has been approved, the project is still at the assessment stage.

The first question for the plant is therefore not “Can you copy this gear?” It is “What evidence do we have for each critical dimension?”

Start with the Documents You Already Have

Before arranging new measurements, look through the plant's existing records. Useful information is often spread across maintenance, procurement, and engineering files.

Look for:

• General arrangement and assembly drawings

• Old spare-parts lists and purchase orders

• Previous quotations from the OEM

• Material certificates

• Gear and pinion inspection reports

• Alignment records

• Installation or shutdown photographs

• Equipment nameplates

• Records of repairs or modifications

An old drawing is useful even if it is incomplete. Mark what has been checked against the machine and what has not. A dimension taken from a decades-old document should not automatically be treated as the dimension of the equipment today; mounting surfaces and support structures may have changed during previous repairs.

Measure the Gear—and the Interface It Fits

A replacement gear must do two jobs. Its teeth must mesh with the pinion, and its body must fit the machine.

For the existing girth gear, the measurement plan may need to cover:

The mounting interface deserves as much attention as the teeth. A gear that has been cut correctly but does not fit the existing bolt pattern cannot be installed during the planned shutdown.

Where access is limited, agree on a field measurement plan before the outage. Some dimensions can be obtained while the gear remains installed; others may only be confirmed after guards, fasteners, or a damaged segment are removed. All site work should follow the plant's isolation and lifting procedures.

Do Not Copy Worn Teeth as If They Were New

An old gear is evidence of its original design, but it is also evidence of years of wear.

Tooth tips may be chipped. Flanks may have lost material. One edge may be worn more heavily than the other. If those worn surfaces are copied directly, the replacement could be manufactured with the wrong tooth form.

The engineer preparing the new drawing must distinguish between:

• Original design geometry

• Manufacturing variation

• Service wear

• Damage from misalignment or overload

• Previous repair work

That is why tooth count and outside diameter alone cannot reliably define every tooth parameter. Measurements should be checked against the mating pinion, any surviving records, and the geometry expected for the drive.

If the old gear has failed prematurely, it is also worth asking why. Reproducing a damaged design without reviewing the pinion, alignment, lubrication, and mounting conditions may reproduce the same failure.

The Existing Pinion Is a Valuable Source of Information

When the girth gear drawing is missing, the pinion drawing—or the pinion itself—can help confirm the gear set's geometry. It should be included in the technical review even if you intend to replace only the girth gear.

Provide or measure, where possible:

• Pinion tooth count

• Tooth geometry and face width

• Material and hardness records

• Shaft and bearing arrangement

• Tooth wear and damage

• Existing contact pattern

The pinion's condition affects the replacement decision. A new girth gear may not give satisfactory service against a heavily worn or damaged pinion. The buyer and manufacturer should agree early whether the pinion will be reused, repaired, or replaced.

Yile Machinery's gears and pinions range covers custom parts for heavy-duty drives. If both components are under review, sending their information together is more useful than requesting two unrelated quotations.

Is a Damaged Segment Enough to Make a Replacement?

A segment can be extremely helpful. It may give the manufacturer access to tooth, joint, material, and mounting features that are difficult to measure on an installed gear.

It may not tell the whole story.

Before relying on a sample segment, confirm:

• Whether it is from the gear currently installed

• Its position and orientation in the assembly

• Whether it has been repaired or modified

• Whether its teeth and joint faces are sufficiently intact to measure

• Whether the other segments are identical

• Whether its mounting dimensions still match the machine

A damaged sample should be treated as one source of evidence, not an unquestionable master part. If the gear has experienced extensive wear or a structural failure, field measurements and other records become even more important.

What Photographs Can—and Cannot—Tell a Manufacturer

Good photographs help establish the gear's construction and the condition of the installation. Include a clear view of:

• The complete drive arrangement

• Gear and pinion mesh

• Segment joints

• Mounting bolts and support structure

• Damaged teeth or cracks

• Part markings and nameplates

Add a scale or a known reference where it is safe and practical to do so. Label the photographs so the manufacturer knows which side, segment, and location each image shows.

Photos are especially useful for planning the next measurement step. They are not a substitute for verified tooth geometry or mounting dimensions. A supplier who gives a final production commitment based only on a handful of images is leaving important questions unanswered.

Agree on the New Drawing Before Production

In a replacement project without OEM documentation, drawing approval is a critical decision point.

The proposed manufacturing drawing should identify:

• Which dimensions came from verified field measurements

• Which data came from old records

• Which features were inferred or reconstructed

• Which details still require buyer confirmation

• Material, heat treatment, and inspection requirements

• The intended mating pinion

Ask the supplier to highlight assumptions instead of hiding them in the drawing. A short list of open technical questions is much easier to resolve before production than a fit problem discovered when the gear arrives.

The purchase order should also state how changes will be handled if a critical site dimension is confirmed only after dismantling begins.

Plan Inspection Around the Actual Risk

Inspection requirements should reflect what is uncertain about the project.

For example, if the main risk is fitting an old shell flange, pay close attention to the mounting-hole layout and interface dimensions. If the tooth specification has been reconstructed, agree on the tooth measurements and reports needed to confirm it. For a segmented gear, define how joints, identification marks, and any specified factory trial assembly will be checked.

Material records, applicable non-destructive testing, hardness results, and dimensional reports should be agreed in the purchase order or inspection and test plan—not requested for the first time before shipment.

Factory inspection confirms the gear against the agreed manufacturing requirements. It does not replace site checks of installed runout, backlash, and tooth contact with the actual pinion.

A Practical Inquiry Checklist

You do not need a perfect package to make an initial inquiry. Send what you have, and clearly mark what is missing.

• Equipment type and model, if known

• Photos of the complete gear-and-pinion drive

• Any old gear or assembly drawings

• Gear tooth count

• Gear outside diameter and face width, if measured

• Number of gear segments

• Segment or damaged-part sample availability

• Mounting-interface information

• Pinion drawing, measurements, or photographs

• Material and inspection records, if available

• Description of current damage and previous repairs

• Planned shutdown and required delivery timing

• Destination country and delivery location

State which figures are measured, which come from documents, and which are only estimates. That simple distinction makes an initial technical review much more productive.

Frequently Asked Questions

Can you quote a girth gear from photographs?

Photographs can support an initial discussion, but they usually do not provide enough information for a firm manufacturing specification. A useful quotation may require verified tooth data, mounting dimensions, segment details, material requirements, and pinion information.

Do we have to stop the mill or kiln to collect measurements?

Not necessarily for every measurement. However, some critical features may be inaccessible while the equipment is assembled or running. Plan measurement access with your maintenance team and do not assume all dimensions can be confirmed without a shutdown.

Can the old gear be used as the only sample?

It can be a major source of information, but wear, damage, and previous repairs may make some of its features unreliable. The proposed drawing should be checked against the pinion, mounting interface, and available records.

Should we replace the pinion as well?

That depends on its condition and compatibility with the new gear. Inspect its teeth, shaft, bearings, and contact history before deciding to reuse it. A worn pinion can shorten the life of a new girth gear.

What if our old drawing does not match the installed machine?

Treat the installed machine as an important source of evidence and investigate the difference. Previous repairs or modifications may have changed the mounting arrangement. Do not release the replacement drawing until critical discrepancies are resolved.

Can Yile Machinery review a project with incomplete drawings?

Yes. Send the available documents, photographs, measurements, and equipment details for an initial review. We can identify which information is sufficient for the next step and which critical points still need confirmation before a manufacturing drawing and production scope can be agreed.

Send Us What You Have

You do not need to reconstruct the entire gear specification before making contact. You do need to be clear about what is known and what remains uncertain.

Send Yile Machinery your old drawings, gear and pinion photographs, available measurements, and a brief description of the machine and its condition. Tell us whether you are planning a future shutdown or responding to a current failure.

We will review the information available for your custom girth gear or pinion project and discuss the next technical steps. You can also browse the Yile Machinery Blog for more articles on heavy-duty industrial components and replacement-part sourcing.