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11.1 Linear Guideways

Linear guideways

The varied areas of application require different characteristics of linear guideways and recirculating units.

Various parameters and considerations are critical for product selection. These are described in detail below.

Cage Length K ⇄ Number of Rolling Elements R_A

Bi-directional conversion between K and R_A

Formula a or b
Cage length
mm
Cage division
mm
Distance from cage start to first rolling element
mm

Stroke H / Guideway Length L Ratio Checker

Stroke / Guideway Length Ratio Checker

Stroke
mm
Guideway length
mm

Relationship between stroke H and length of the guideway L

Relationship between stroke H and length of the guideway L

If the stroke is below 400 mm

If the stroke is below 400 mm

H / L ≤ 0.7

If the stroke is above 400 mm

If the stroke is above 400 mm

H / L ≤ 1
L Length of the linear guideway in mm
Guideway length parameter
H Possible Stroke in mm
Stroke parameter

Calculating the cage length K

Calculating the cage length K

K ≤ L - H₁

If the stroke is symmetrical

If the stroke is symmetrical

H = H₁ + H₂ = H₁₂

If the stroke is asymmetrical

If the stroke is asymmetrical

H = H₁ + H₁
H > H₁ + H₂
H₁₂ = H₁ + H₂
KCage length in mm
Cage length
LLength of the linear guideway in mm
Guideway length
HPossible Stroke in mm
Possible stroke
H₁Large partial stroke in mm = H/2
Large partial stroke
H₂Small partial stroke in mm = H/2
Small partial stroke
H₁₂Effective partial stroke in mm
Effective partial stroke
Important: The stroke must be limited by means of stops on the table and not by the cages. The stops should preferably be fitted along the axis of symmetry of the guideways to avoid additional forces acting on the linear guideways.

Calculating the number of rolling elements (R_A) per cage

Calculating the number of rolling elements (R_A) per cage

a) For cage types: KBN, AA-RF, AC, AK, EE, SHW, HW

For cage types KBN, AA-RF, AC, AK, EE, SHW, HW

Cage type a
K = (RA - 1) · t + 2 · w ⇒ RA = (K - 2 · w) / t + 1

or

RA = Kt / t + 1

b) For cage type: KBS

For cage type KBS

Cage type b
K = (RA - 2) · t + tz + 2 · w ⇒ RA = [K - (2 · w + tz)] / t + 2

or

RA = (Kt - tz) / t + 2
KCage length in mm
Cage length
tCage division in mm
Cage division
RATotal available rolling element per cage
Total rolling elements per cage
KtLoad-bearing length in mm
Load-bearing length
wDistance from cage start to the middle of the first rolling element in mm
Distance to first rolling element
tzLength of the middle section for the KBS cage
Middle section length (KBS)

The relationship between the cage length K and the average guideway spacing Q

The relationship between the cage length K and the average guideway spacing Q

K / Q ≥ 1
Relationship between cage length and guideway spacing
KCage length in mm
Cage length
QAverage linear guideway spacing in mm
Average guideway spacing

The maximum permissible installation ratio in the case of overrunning cages

The maximum permissible installation ratio in the case of overrunning cages

Overrunning cage illustration

Overrunning cages are expedient if a short table is to be moved on a long guideway track. In each case the short rail for the guideway must have a rounded run-in (special version EG, see chapter 7.3) so that the overrunning cage causes as little pulsation as possible.

Not every cage is suitable for this application. The maximum cage overrun depends on the position of the rails and on the cage material.

Maximum permitted installation ratios L : L₁

Maximum permitted installation ratios L to L₁:

for fixed guideways
Fixed guideway installation		 1 : 2
for laid on guideways
Laid-on guideway installation		 1 : 4

Installation variants for linear guideways

Installation variants for linear guideways

There are four installation variants for linear guideways. The various linear guideways can be also used with wipers in the form of end pieces (a₁)*. In these four cases, the following length ratios result:

Variant 1

Linear guideway with:
  • Equal length rails
  • Symmetric / asymmetric stroke
Variant 1 configuration

a) Without end screws, end pieces, and end pieces with wipers

Without end screws, end pieces, and end pieces with wipers

K ≤ L - H₁
Ltot = L + H₁ + H₂

b) For end screws, end pieces, and end pieces with wipers**

For end screws, end pieces, and end pieces with wipers**

K = L - H₁
Ltot = L + H₁ + H₂ + 2 · a₁

Variant 2

Linear guideway with:
  • Equal length rails
  • Unidirectional stroke
Variant 2 configuration

a) Without end screws, end pieces, and end pieces with wipers

Without end screws, end pieces, and end pieces with wipers

K ≤ L - H₁
Ltot = L + H₁

b) For end screws, end pieces, and end pieces with wipers**

For end screws, end pieces, and end pieces with wipers**

K ≤ L - H₁ - a₁
Ltot = L + H₁ + a₁
With this design, the linear guideways must be staggered to one another by the amount a₁.

Variant 3

Linear guideway with:
  • Unequal length rails
  • Symmetric / asymmetric stroke
  • Short rails attached
Variant 3 configuration

a) Without end screws, end pieces, and end pieces with wipers

Without end screws, end pieces, and end pieces with wipers

K ≤ L - H₁
Ltot = L + H₁ + H₂

b) For end screws, end pieces, and end pieces with wipers**

For end screws, end pieces, and end pieces with wipers**

K ≤ L - H₁ - 2 · a₁
Ltot = L + H₁ + H₂

Variant 4

Linear guideway with:
  • Unequal length rails
  • Symmetric / asymmetric stroke
  • Long rails attached
Variant 4 configuration

a) Without end screws, end pieces, and end pieces with wipers

Without end screws, end pieces, and end pieces with wipers

K ≤ L - H1
Ltot = L + H1 + H2 (when L ≥ L1 - H12)
Ltot = L1 (when L ≥ L1 - H12)

b) For end screws, end pieces, and end pieces with wipers**

For end screws, end pieces, and end pieces with wipers**

K ≤ L - H1 - a1
Ltot = L + H1 + H2 + 2 · a1 (when L ≥ L1 - H12)
Ltot = L1 (when L ≥ L1 - H12)

Parameters

KCage length in mm
Cage length
HPossible stroke in mm
Possible stroke
H₁Large partial stroke in mm = H/2
Large partial stroke
H₂Small partial stroke in mm ≤ H/2
Small partial stroke
totEffective partial stroke in mm
Effective partial stroke
LLength in mm
Guideway length
L₁Length in mm
Long-rail length
LtotTotal length in mm
Total length
anThickness of the end piece in mm
End piece thickness

* a₁ end screws, end pieces, and end pieces with wipers, see chapter 5

** Wipers can influence the run characteristics of the linear guideways

ESC