Special Bearings - Custom Steel Bearing Units | GMN Bearing USA

Custom Special Bearings

special bearings

Besides high precision spindle bearings and radial deep groove ball bearings GMN produces special bearings, matched bearings with spacers and oil supply rings as well as bearing units ready to install.

These bearings are made either from standard bearing steel 100 Cr6 or from special material like high temperature tool steel or non-corrosive steel AISI 440C.

Standard bearings with different dimensions or outlines are available on request.

The cages of these bearings are produced in accordance to the inner design of the bearing and corresponding to the application either standard materials or special materials like VESPEL, TORLON, aluminum, bronze or NiBe2 are used.

Bearing units

It becomes more and more important to support the customers not only in developing efficient products and system solutions but also in manufacturing sub assemblies. Therefore, GMN extended the production range to offer complete bearing units ready to install.

special bearing

These units develop from the customer¹s knowledge of product requirements and GMN¹s experience in high precision machining.

In addition, GMN can apply on the bearings various coatings like solid lubricants or wear protection layers. Please check with vacuum technology/dry lubrication.

To produce special bearings or bearing units, economic lot sizes are required.



For certain applications, it is impossible to use standard ball bearings. Limited space, special lubrication, guidance, sub-functions often do not allow additional machine parts. Then a standard bearing has to be adapted to a specific application.

The department "Special Bearings" assists in these adaptations. GMN is fully experienced in this section, due to a long co-operation with GMN Spindle Division and universities on special products. The spectrum ranges from different dimensions and outlines of the bearing parts and precision bearings for linear motions to bearings for extreme conditions like high vacuum and temperatures up to 500° C (932° F).

In the same way GMN produces bearings to customer's specification plus associated components like spacers with and without oil feeding, complete bearing units and respective subassemblies.

The special bearings and bearing units (P4, HG, UP, P2) are produced on special machine tools in utmost precision. Because of the present machinery at GMN, the production is limited to the following dimensions.


Today, the limits are as follows
- max. outer diameter 120 mm
- min. inner diameter 5 mm
- max. width 25 mm

Examples & Applications

Precision linear guide

Bearing design:

  • Special design of the outer ring


  • Precision linear guide

Vacuum pump

Bearing design:

  • Special design of the outer ring
  • Special cage design


  • Vacuum pump, oil feeding cage design

Spray gun

Bearing design:

  • Extra wide bearing with shields


  • Spray gun,n= 40.000 rpm

High frequency spindle

Bearing design:

  • Spindle bearing combined with spacer and respective oil feeding rings to increase the spread and to improve oil supply


  • High frequency spindle

nautical gyroscope

GMN high precision special bearings for nautical gyroscopes are approved for low and constant running torque, long life time and utmost reliability.

turbo molecular pump

GMN high precision special bearings for turbo molecular pumps are approved for low noise, high running accuracy and highest reliability.


To obtain the best possible performance of the bearings, installation must be performed very carefully in ultra clean conditions.

Errors during fitting of ball bearings can jeopardize the best design and create high repair and maintenance costs. We would like to give some advise for proper mounting of bearings:

The workshop should be dust free with low humidity, no compressed air or machining is allowed.

Only unpack bearings immediately before installation. If grease is required it should be applied at this time, with a syringe. Do not use fingers or a spatula.

The use of a syringe is recommended to inject the grease right between the balls into the ball/raceway area. Nearly all standard greases are compatible to our rust preventive, so in most cases it is not necessary to wash the bearings prior to greasing. The only exceptions are special greases, based on silicone or fluorocarbon oils or PTFE-thickeners. They require a clean oil free surface to obtain good adhesion of the grease.

Never clean the bearings in ultra sonic devices! Allow the rust preventive to dissolve in a gasoline bath by slowly moving the bearings.

It is recommended to use filtered cleaning gasoline type 100/140 (max. filter 0.45 microns). Drying of the bearings should take place under a dust cover. Bearings should never be dried by blowing with compressed air because of environmental dust and moisture!

Finally the bearings, ready for installation, can be mounted by adequate means. It is of utmost importance to avoid misalignment of the bearings in the seats and that mounting loads never be applied through the balls.

The following pictures illustrate the correct installation:

special bearing correct insallation

The red lines show the line of force while pressing the bearings onto their seats. The sketch on the right shows the mounting forces passing through the balls. This leads to indentations in the raceways hence the bearings run noisy and the service life will be reduced.

bearing correct mounting

This sketch shows the correct mounting of a bearing with a tight bore fit onto the shaft. Mounting forces are conveyed through the inner ring only, balls and races remain free and undamaged.

special bearings

Very few applications call for tight fits on both bearing seats. In this case a bearing can be mounted by pressing both rings simultaneously. As a result, balls and raceways remain undamaged.

Starting operation

Oil lubrication

In general, there are no particular running-in specifications for oil lubed bearings, nevertheless it proved advantageous when

  • lubricant is available prior to start up. Consider length of feed pipes to avoid insufficient lubrication,
  • when performing a short running-in procedure to allow the bearings to settle in their seats.

Grease lubrication

Grease lubrication calls for running-in of the bearings. Even when a reduced grease pack is applied to the bearing, a certain amount of surplus grease causes additional friction. A complete grease film must cover all contact surfaces.

GMN recommends the following procedure for the majority of applications:

  • Starting sequence at 10 per cent of operating speed followed by a stop to allow the bearings to cool off to ambient temperature.
  • Distribution sequence at 50 per cent of operating speed where actual operating temperature slightly exceeds final operating temperature. When the temperature has reached a maximum, the unit is stopped to cool off again to ambient temperature. Test sequence, first operate at nominal speed. If target operating temperature is exceeded, the distribution sequence should be repeated.
  • Length and number of sequences depend on specific properties of the application. Grease reservoirs, limited space, operating speed and environmental media have a strong effect on the distribution of the grease.

How long and how often this procedure is to be repeated depends on the properties of the application. To optimize the running-in process for your specific application, please contact our application engineers.

Click here or call 1.800.323.5725 to Request a quote

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