7/22/2019 Back Marks, Cross Centres and Pitch

1/9

Back marks, Cross centres

and Pitch

Aims and objectives1. To be able to identify where the back mark

measurement is taken from2. To understand the relationship between theback mark length and the flange length of thesection.

3. To be able to identify where the cross centres

measurement is taken from.4. To identify the practical application of the PCDmeasurement and how it is used in conjunctionwith the line of chord calculation

5. To identify a linear pitch.

7/22/2019 Back Marks, Cross Centres and Pitch

2/9

Leg Length(MM)

Hole centreS1 (MM)

25 15

30 2045 25

50 28

60 3575 45

90 50

100 50

Backmark for Equal leg RSA

7/22/2019 Back Marks, Cross Centres and Pitch

3/9

Backmarks for Unequal leg RSA

Leg

length

(MM)

First

hole

centre

S2

Second

Hole

centre

S3

125 45 50150 55 55

200 75 75

7/22/2019 Back Marks, Cross Centres and Pitch

4/9

Leg

Length(MM)

Hole

centreS4

Hole

centreS5

Hole

centreS6

200 55 55 55

Backmarks for Unequal leg RSA

(cont)

7/22/2019 Back Marks, Cross Centres and Pitch

5/9

7/22/2019 Back Marks, Cross Centres and Pitch

6/9

Flange width

(MM)

Cross

CentresS1

102 54

127 70146 70

165 90

178 90

210 140

305 140

7/22/2019 Back Marks, Cross Centres and Pitch

7/9

7/22/2019 Back Marks, Cross Centres and Pitch

8/9

7/22/2019 Back Marks, Cross Centres and Pitch

9/9