Page 106 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Required passover
Passover measurement
1st bend

1
Close a folding rule down to the passover measurement
to obtain the angle for the first bend
Angle required
Passover measurement

600 mm rule
2
Bend tube to the angle required by the folding rule
3
Close folding rule down to twice the passover measurement
to obtain the angle for the second bend
2 × passover
measurement

The City & Guilds Textbook: Plumbing Book 1 Angle for second bend
Required passover 4
Mark for the second bend by measuring
from the inside edge of tube
Passover measurement
1st bend Bending mark
Passover
measurement
1 Straight edge
Close a folding rule down to the passover measurement
to obtain the angle for the first bend
Passover measurement Angle required
5
Re-position tube in the machine so that
mark forms a tangent to the former
600 mm rule
2
Bend tube to the angle required by the folding rule

3
Close folding rule down to twice the passover measurement
to obtain the angle for the second bend

2 × passover
measurement

Angle for second bend

p Figure 2.13 Partial passover bends
4
Mark for the second bend by measuring
from the inside edge of tube
KEY POINT Rippling or throating of tube in machine-
Bending mark
If pressure is exerted made bends
Passover
too far forward of the Straight edge measurement
bending point, then Bending machines are designed to give a 4 diameter bend and so that the
ripples will occur. If former and the bending guide supports the throat and sides of the tube against
the roller is tightened collapse. Ripples will occur in the throat of a bend if the pressure of the roller
too much the pressure on the guide is insufficient or in the wrong place. The correct pressure point
5
point will be too far back is slightly in front of the bending position, where the tube touches the former
Re-position tube in the machine so that
and the tube will be before the actual bending process occurs.
mark forms a tangent to the former
excessively ‘throated’ or
made oval in section. With scissor (handy) benders, rippling occurs with use. This is because the bending
former, being made of aluminium, stretches over time and, because the pressure
KEY TERM roller is fixed, it cannot be tightened or repositioned to give the correct bending
pressure. If ripples appear when using fixed-position ‘handy benders’, the pressure
Throat: the inside face. point can be readjusted by inserting a thin piece of strip steel (the thickness of a

hacksaw blade) between the guide and the roller to cure the problem.

94

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