Page 9 of catalogue Linear bearings of PM Bearings B.V.

Calculation of Cage Length "K" Cages travel at half the speed of moving linear bearing track and through half the distance...ie: the stroke of the cage equals half the stroke of the moving bearing member, or the slide top: K=H/2. But with a normal "frictionless" slidingtable, the upper member can move equal distances to either side of the centre. K=A-H/2 (ie: cage length= guideway length - half of the max. stroke) The relationship between the cage length and the distance between the guideways (x); K/x ≥ 1

Load Capacity "C" by using Balls The normal linear bearing construction incorporates two pairs of guideways (of equal length) with two shorter ball cages, one between each pair of guideways. Note: all the balls in the cages are load bearing. Ctotal=Z x Cball = (no. of balls) x (load rating per ball). Example: cage K3 x 23JJ; Z=23; Cballs=30 N per ball. Ctotal=23 x 2 x 30=1380 N. Calculation of Number of Rollers "Z" Z= K:t ... whereby : K= cage length t= pitch between rolling elements Example K= 200 mm (length of cage) t= 5 mm (for 3mm dia-rollers or –balls) Z= 200:5 = 40 rollers or balls.

a

A

a

H/2 A H/4 K H/4
x

a

H

A

a

Atot = A+H+2a

Cage Designation: Examples (assuming that the appropriate load calculations have been done) R3 x 40AA; roller size=3 mm; 40 rollers; horizontal movement. R6 x 18DD; roller size=6 mm; 18 rollers; vertical movement. K3 x 20JJ; ball size= 3mm; 20 balls; vertical movement. R1.5x 6KZR; roller size=1.5 mm; 6 rollers; vertical movement. Note: for roller/ ball size ≥ 6 mm, please specify the roller/ball-pitch required. Table Loadratings balls/rollers (mat. 100Cr6)

K= Cage length H= Stroke/travel A= Guideway length Atot= Overall length

x= a=

Guideways distance (average) Endscrews

Load Capacity "C" by using Rollers Standard constructions with rollers: two roller cages, each interposed between a pair of linear bearing guideways of equal length, both longer than the cage. (ie: 4 bearing track-rails, in all). Ctotal=Z x Croller x 1⁄2 (no. of load-bearing rolling elements) x ( roller load rating) x 1⁄2. Normally only half of the total number of rollers will be load bearing; the other half resists possible lift-off forces. (there is one exception: all rollers will be load bearing if a pair of rails is installed horizontal, but one above the other, with the V-guideway of the lower rail facing up and that of the upper rail facing down; ie: in the direction of the applied load, assumed here to be vertical). Example: assuming a normal horizontal installation, with two roller cages R3x22AA; Z=22 and Croller=136 N/roller. Ctotal= (22 x 2 x 136) : 2= 2992 N.

Size (mm) 1.5 2 3 4 6 9 12 15 Note
1 2

Loadratings Balls Europe1 10 21 30 48 78 150 260 420

per ball/roller (N) Rollers Japan2 Europe1 Japan2 21.6 52 118 39.2 86 206 87.3 136 461 155 265 911 353 540 2240 784 1350 4410 1420 2560 7450 2160 4500 12000

: Based on European industrial standards : Based on Japanese industrial standards

Loadratings for crossed rollerways are listed in the Tables for ready-to-install sets.

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