Clearance - Bearings - Technical
The clearance or radial play of a bearing is equal to the total radial displacement, in the median plane perpendicular to the bearing axis of the inner ring in relation to the outer ring, under the effect of a small measuring force.
Exagerated depiction of various levels of Radial Play. The starting amount is also adjusted by other factors such as housing tolerances, loads and temperature.
Because of the complexity of measurement and taking into consideration manufacturing tolerances, radial play is always indicated between two limits. Normal clearance for miniature bearings is considered to be 5 to 15 um (.0002 to .0006").
MBA bearings are usually further broken down into sub groups using the precision miniature bearing clearance scale MC1 to MC6. Refer to the chart below.
Clearance (play) is not one of the criteria of bearing quality but if badly chosen or unfavourably influenced during mounting, it can adversely affect the operation and even reduce the working life of a bearing.
Miniature bearing clearances (MC1 to MC6) are not the same as large bearing clearances (C1 to C5 and CN). Miniature clearances more accurately grade bearings under 10mm bore.
MC3 IS NOT C3.
To confuse the issue, bearing manufacturers that don't specialise in the miniature market often don't use miniature clearance designations because the clearances to which they manufacture are not precisely controlled.
A miniature bearing without a clearance designation is usually made to a large clearance range. For example, 624-2RS or 624-ZZ bearings with no clearance designation could have an internal clearance anywhere within the range 5 to 20 microns. It's quite a wide range which is usually ok for everyday applications.
Precision miniature bearing clearances are broken down into more precise groups. MC3 and MC4 can both be considered "standard". MC3 clearance range is 5 to 10 microns and MC4 is 8 to 13 microns. In precision applications, selecting the correct clearance can be critical, but in everyday applications both MC3 and MC4 bearings can be supplied as standard. They are both within the specifications of "standard clearance", just more precisely graded.
MBA also have a designation MC34 to indicate that a bearing falls within the range of MC3 to MC4, 5 to 13 microns. It's just a broader range that still falls within the definition of "standard".
Further, clearances that don't conform to the MC1 to MC6 scales can be organised in special manufacturing batches.
The table below lists standard miniature clearances. Additional special clearances which don't fall into the below ranges will be designated with CX-Y where "X" is the lowest acceptable clearance and "Y" is the largest acceptable clearance in microns. For example a bearing with a clearance of C8-23 has a wide range from 8 to 23 microns, whilst a bearing with a clearance of C10-15 has a tightly controlled clearance of no less than 10 microns and no more than 15 microns.
Miniature Bearings (Less than 10mm bore size)
This table shows the basic radial clearances available for miniature bearings and applications for these clearances. Dimensions shown in microns um 0.001mm and (10000ths of an inch 0.0001").
|MC1||MC12||Tight||0 (0)||5 (2)||Radially loaded low backlash gear systems. Very low speed.|
|MC2||3 (1)||8 (3)|
|MC3||MC34||Standard||5 (2)||10 (4)||Tape Guides, Synchros, Servo Motors, Low Speed Electric Motors and Gear Trains. Gyro Gimbals (Horizontal Axis).|
|MC4||8 (3)||13 (5)|
|MC5||MC56||Loose||13 (5)||20 (8)||High speed Electric Motors and Tape Guides. Provides some compensation for axial loading. Gyro Gimbals (Vertical Axis).|
|MC6||20 (8)||28 (11)|
Bearings 10mm bore size and over
This table shows the basic radial clearances available for bearings over and including 10mm bore size. Dimensions shown in microns um 0.001mm.
|Bore Size Range|
|Min / Max Clearance|
|ISO/MBA Code||Description||10mm Only||Over 10mm to 18mm||Over 18mm to 24mm||Over 24mm to 30mm||Over 30mm to 40mm||Over 40mm to 50mm|
|C2||Tight||0 to 7||0 to 9||0 to 10||1 to 11||1 to 11||1 to 11|
|CN (standard)||Standard||2 to 13||3 to 18||5 to 20||5 to 20||6 to 20||6 to 23|
|C3||Loose||8 to 23||11 to 25||13 to 28||13 to 28||15 to 33||18 to 36|
|C4||14 to 29||18 to 33||20 to 36||23 to 41||28 to 46||30 to 51|
|C5||20 to 37||25 to 45||28 to 48||30 to 53||40 to 64||45 to 73|
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Extra information for Technical - Bearings
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