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Technical Memo

Reconditioning Large Gears

It is possible to recondition gears, even after years of wear. This Process is particularly beneficial today because of the significant Investment Level and long Lead Times for Gears.


Reconditioning results in lower cost. By Reconditioning your gear the center section and hub is conserved, saving thousands and thousands of dollars.

Deliveries are significantly less than that of a new gear.

HMC's Reconditioned Drive Solutions

HMC has many years of experience in reconditioning gears; particularly large coarse pitch gears used in mining, grinding, and other ball mill applications. The procedures and manufacturing processes we have developed offer a "Reconditioned Drive Solution".

It is our goal to provide gearing solutions that will meet or exceed our customer's circumstances at as reduced an investment level as possible.

The following procedures and processes evolving through years of experience are tried and tested.

Evaluating candidate for reconditioning

The gears are thoroughly cleaned.

Following cleaning, the gears receive a full inspection, to determine the integrity of the gear blank for reconditioning. This inspection includes:

  • Full dimensional inspection. Quality reconditioning involves more than just re-cutting the teeth. Dimensions out of tolerance and requiring rework are assessed.

  • The entire gear blank is checked for cracks by Magnetic Particle Testing. This procedure identifies surface cracks that must be detected and repaired prior to any re-machining efforts.

  • When there is suspicion of sub-surface troubles the blank is further tested ultrasonically to locate subsurface disparities. Although all materials have subsurface irregularities, the ASTM (American Society for Testing Metals) and AGMA (American Gear Manufacturer’s Association) have established limits as to the number and size of irregularities for a given area. The actual number is compared to the allowable to determine if the parameters meet the minimum requirements of these specifications.

  • Following testing for material integrity the rim thickness, tooth thickness, tooth size, and wear to the teeth are measured to estimate whether or not the gear blank is a candidate for reconditioning. Essentially, is there is material enough for generating a new tooth?

  • Calculations derived from AGMA Standards are then performed by an engineer to determine if the Re-cut Tooth will have adequate capacity.

  • Loading and Mounting Center Distances must be supplied by customer.

  • Since the reconditioning of a large gears often times involves reducing the outside diameter of the gear to allow undamaged material to become available for the new teeth to ensure proper meshing actions, an "oversized" pinion is required. Engineering performs the necessary calculations to determine the parameters for the Mating Pinion.

Following these inspections and engineering requirements a report describing the issues discovered during inspection, the required work scope, recommended correction actions, and pricing for the above, is forwarded to the customer.

The Reconditioning Process after Customer Approval:

Regardless of whether weld repairs are required the Gear will undergo a Pre-reconditioning Stress-Relieve the gear prior to any machining operations.

Any Joint Hardware is replaced with all new hardware

Mounting and mating surfaces are trued; the bore, the faces of the hub and rim, any joint flanges or splice plate-mounting surfaces. This assures a quality fit along with machined reference surfaces required for the gear reconditioning processes as well as reassembly and alignment of the gear.

The OD is turned (if applicable)

The teeth are re-cut according to the new specification.

Re-cut gear accuracies can often be better than that of the original gear resulting in improved alignment

The new profile and runout measurements are recorded as a permanent record. Copies are available to the customer if requested.

A Thorough Inspection of the Gear is then performed

One of HMC's Professional Cosmetologists then preps the Gear

The Reconditioned Gear is then Professionally Painted and Crated

When Modified Pinions are part of the Work Scope for a Reconditioned Drive Solution they will be manufactured from quality materials and hardness that is compatible to the gear, while receiving all of the above described services applicable.

The pinion will be scheduled for completion to meet a delivery comparable to the gear.

It is important for the Customer to understand the interchangeability options that may exist with their reconditioned gear and new, oversized pinion (if applicable).

Will my Reconditioned Gear work with pinions I currently own?

Reconditioning of large gears usually eliminates the possibility of using existing spare pinions owned by the customer. After the Gear OD is turned and the teeth are re-cut the geometry of the gear mesh is changed enough to impede original spares from functioning satisfactorily. Although they might outwardly seem to fit and mesh they will under power immediately operate with considerable vibration and noise and cause greatly accelerated wear and damage to the gear with continued operation.

The original condition of the worn gear determines the amount of stock HMC has to remove from the used gear to bring it back into good working order. The amount of stock be removed is what will determine if it will function satisfactorily with an originally design pinion.

When adjustable center distances are part of the Customer's Machinery there will be occasions when the Reconditioned Gear may be acceptable to operate with an original spare pinion or the HMC Oversized Pinion may be acceptable to operate with an original design gear. However these issues must be considered, discussed, and approved in writing by HMC.

When a Reconditioned Gear has been properly installed and aligned against an HMC Designed Oversized Pinion and properly Lubricated and Maintained the Gear Set should offer the Customer several years of service.

Initial Budgetary Quote

Although we attempt to consider and anticipate all of the your requirements when estimating a Reconditioned Gear certain aspects you may require cannot be determined until your gear is at our facilities and fully cleaned, and fully inspected. For this reason, out initial quotation of your Reconditioned Gear Set is "Budgetary". If and when our anticipated work scope for your Gear changes we will contact you with the details, prior to proceeding.

Let Us Help you

We will help you decide if reconditioning is an option or not. Our 24/7 Manufacturing Infrastructure is always available to you and only a phone or e-mail message away. Please contact us any time we can be of assistance to you on any matter; (Technical Information, Replacement Parts - (Normal or Rush)!

HMC Gears • 3010 S. Old US Hwy. 41 • Princeton, IN • 47670 • 866-990-9462

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