Precision Bearings: Precision Grade and Tolerance

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One of the factors you will definitely want to take into account when purchasing ball bearings is the issue of precision. There are two types of precision for Ball Bearings. One is dimensional accuracy and the other is rotational accuracy. Dimensional accuracy for bearings is a measure of the error between the actual dimensions of the bearings (bore diameter, outer diameter, inner ring width, outer ring width) and the target value for these dimensions. Rotational accuracy, or runout, measures the degree of eccentricity of a bearing, and can be measured for side, axial, or radial runout of the inner or outer ring. A higher level of radial runout, for example, means more vibration at higher speeds for that bearing. The standards that control both are written by JIS and ABMA. NMB uses JIS B1514 /ISO 492, ABMA Standard 12-2 and Standard 20. The following symbols are used in this catalog:  
The bearings are classified into certain precision grades. The tolerances for each grade are found in JIS and ANSI/ABMA. Minebea’s products are based on JIS B 1514-1,-3, ANSI/ABMA Std.12.2 and ANSI/ABMA Std.20 The symbols used in the specification are as follows.

Symbol

Dimensions

d : Nominal Bore Diameter
D : Nominal Outside Diameter
D1 : Outer ring flange outside diameter, basic
B : Nominal Inner Ring Width
C : Nominal Outer Ring Width
 r : Chamfer Dimension of Inner Ring or Outer Ring

Dimensional Differences

Δds : Dimensional difference of bore diameter
Δdmp : Dimensional difference of mean bore diameter in the plane
(Δdm) : Dimensional difference of mean bore diameter
ΔDs : Dimensional difference of outside diameter
ΔDmp : Dimensional difference of mean outside diameter in the plane
(ΔDm) : Dimensional difference of mean outside diameter
ΔBs : Dimensional difference of inner ring width
ΔCs : Dimensional difference of outer ring width
ΔD1s : Deviation of a single flange outside diameter
ΔC1s : Deviation of a single width of the outer ring flange

Limit Values of Chamfer/Radius Dimension

rs : Chamfer dimension of inner ring or outer ring
rs min : Minimum dimension limit of inner ring and outer ring chamfer
rs max : Maximum dimension limit of inner ring and outer ring chamfer

Inequality of Dimensions

VBs : Inequality of inner ring width
VCs : Inequality of outer ring width
VC1s : Inequality of flanged width

Rotation Precision

Kia (Ki) : Radial runout of inner ring
Sia (Si) : Axial runout of inner ring
Sd (Sdi) : Side runout of inner ring [runout of inner ring reference face with respect to the bore]
Kea (Ke) : Radial runout of outer ring
Sea (Se) : Axial runout of outer ring
SD (SD) : Side runout of outer ring [variation of outside surface generatrix inclination with respect to the outer ring reference face]
SD1 : [variation of outside surface generatrix inclination with respect to the outer ring flange back face]
Seal : Axial runout of outer ring flange back face

Remark (  ) is defined by ANSI/ABMA. Reference [  ] is the expression used in previous JIS. Attention : Above is only for radial ball bearing.

 

Referred from JIS B 1514-1

Tolerance of inner ring d ≦ 18mm

(Unit : μm)
Grade Dimensional difference Radial Runout Perpendicularity Axial runout Dimensional difference of width Inequality of width
Δdmp Δds Kia Sd Sia ΔBs VBs
Upper Bottom Upper Bottom MAX MAX MAX Upper Bottom MAX
Grade 0 0 -8 - - 10 - - 0 - 40*1 -120 12*1 15*2 20
Grade 6 0 -7 - - 5*1 6*2 7 - - 0 - 40*1 -120 12*1 15*2 20
Grade 5 0 -5 - - 4 7 7 0 - 40*2 - 80 5
Grade 4 0 -4 0 -4 2.5 3 3 0 - 40*2 - 80 2.5
Grade 2 0 -2.5 0 -2.5 1.5 1.5 1.5 0 - 40*2 - 80 1.5
*1 the values apply only up to and including d = 2.5mm. *2 the values apply only up to and including d = 10mm.

 

Tolerances of outer ring D ≦ 30mm

(Unit : μm)
Grade Dimensional difference Radial runout Perpendicularity Axial runout Dimensional difference of width Inequality of width
ΔDmp ΔDS Kea SD Sea ΔCs VCs
Upper Bottom Upper Bottom MAX MAX MAX Upper Bottom MAX
Grade 0 0 -8*1 -9 - - 15 - - 0 - 40*2 -120 12*2 15*3 20
Grade 6 0 -7*1 -8 - - 8*1 9 - - 0 - 40*2 -120 12*2 15*3 20
Grade 5 0 -5*1 -6 - - 5*1 6 8 8 0 - 40*3 - 80*4 5
Grade 4 0 -4*1 -5 0 -4*1 -5 3*1 4 4 4 0 - 40*3 - 80*4 2.5
Grade 2 0 -2.5*1 -4 0 -2.5*1 -4 1.5*1 2.5 1.5 1.5*1 2.5 0 - 40*3 - 80*4 1.5
*1 the values apply only up to and including D = 18mm. *2 the values apply only up to and including d = 2.5mm. *3 the values apply only up to and including d = 10mm. *4 the values apply only up to and including d = 18mm.

Flange outside diameter tolerance

(Unit : μm)
D1 Column 1 Column 2
(mm) ΔD1s
Over Incl. Upper Bottom Upper Bottom
10 +220 -36 0 -36
10 18 +270 -43 0 -43
18 30 +330 -52 0 -52
Remarks : When the flange outside diameter is used for location, column 2 shall apply.

 

Tolerances of flange width and tolerance of rotation precision related to flange

(Unit : μm)
D Grade 0, 6 Grade 5, Grade 4, Grade 2 Grade 0, Grade 6 Grade 5 Grade 4 Grade 2
(mm) ΔC1s VC1s
Over Incl. Upper Bottom Upper Bottom MAX
2.5*1 30 0
-40*2
-120
0 -40*3 -80 12*2 15*3 20 5 2.5 1.5

 

(Unit : μm)
D Grade 5 Grade 4 Grade 2 Grade 5 Grade 4 Grade 2
(mm) SD1 Sea1
Over Incl. MAX MAX
2.5*1 18 18 30 8 8 4 4 1.5 1.5 11 11 7 7 3 4
*1 D = 2.5mm is included in this dimension division. *2 the values apply only up to and including d = 2.5mm. *3 the values apply only up to and including d = 10mm.

 

Referenced from ANSI/ABMA Std.12.2

Inner Ring tolerance d ≦ 18mm

(Unit : μm)
Grade ABEC Δdmp* Δds Ki Sdi Si ΔBs VBs
Upper Bottom Upper Bottom MAX MAX MAX Upper Bottom MAX
3P 0 -5.1 +2.5 -7.6 5.1*1 7.6 - - 0 -127 -
5P 0 -5.1 0 -5.1 3.8 7.6 7.6 0 -25.4 5.1
7P 0 -5.1 0 -5.1 2.5 2.5 2.5 0 -25.4 2.5
9P 0 -2.5 0 -2.5 1.3 1.3 1.3 0 -25.4 1.3
* Basically, grade 3P is provided as Δdm. *1 the values apply only up to and including d = 10mm.

Outer Ring tolerance D ≦ 30mm

(Unit : μm)
Grade ABEC ΔDmp* ΔDs Ke SD Se ΔCs VCs
Open shield/seal
Upper Bottom Upper Bottom Upper Bottom MAX MAX MAX Upper Bottom MAX
3P 0 -7.6 +2.5 -10.2 +5.1 -12.7 10.2 - - 0 -127 -
5P 0 -5.1 0 -5.1 +1 -6.1 5.1 7.6 7.6 0 -25.4 5.1
7P 0 -5.1 0 -5.1 +1 -6.1 3.8 3.8 5.1 0 -25.4 2.5
9P 0 -2.5*1 -3.8 0 -2.5*1 -3.8 - - 1.3*1 2.5 1.3 1.3*1 2.5 0 -25.4 1.3
* Basically, grade 3P is provided as ΔDm. *1 the values apply only up to and including D = 18mm.

 

Referred from ANSI/ABMA Std.20

Inner Ring tolerance d ≦ 18mm

(Unit : μm)
Grade ABEC Δdmp Kia Sia ΔBs VBs
Upper Bottom MAX MAX Upper Bottom MAX
1 0 -8 10 15*1 20 0 0 - 40*1 -120 12*1 15*2 20
*1 the values apply only over and including d = 0.6mm or up to and including d = 10mm. *2 the values apply only up to and including d = 10mm.

Outer Ring tolerance D ≦ 30mm

(Unit : μm)
Grade ABEC ΔDmp Kea Sea ΔCs VCs
Upper Bottom MAX MAX Upper Bottom MAX
1 0 -8*1 -9 15 15*2 20*1 25 0 - 40*3 -120 12*3 15*4 20
*1 the values apply only up to and including D = 18mm. *2 the values apply only up to and including D = 6mm. *3 the values apply only up to and including d = 2.5mm. *4 the values apply only up to and including d = 10mm.

 

Referenced from JIS B 1514-3

Maximum values of chamfer dimension for radial bearings

(Unit : mm)
rs min d rs max
Over Incl. Radial direction Axial direction
0.05 0.08 0.1 0.15 0.2 - - - - - - - - - - 0.1 0.16 0.2 0.3 0.5 0.2 0.3 0.4 0.6 0.8
0.3 - 40 40 - 0.6 0.8 1 1
0.6 - 40 40 - 1 1.3 2 2
1 - 50 50 - 1.5 1.9 3 3

 

Precision Grading: Bearing Corner Radius Bearing Corner Radius