#
What is meant by mean diameter?

When forming metal into a curved shape, metal fabricators must always
allow for the centre measurement of the metal remaining constant. This
is called the neutral
axis. The outside surface stretches
and the inside surface contracts.

The neutral axis is better known as the mean
diameter (MD).

### Calculating the mean diameter

Mean diameter = inside diameter + one plate thickness (of the material
used)

MD = ID + T

or

Mean diameter = outside diameter - one plate thickness

MD = OD -T

### Calculating mean circumference

The mean
circumference (MC) is also the cutting length. Use the formula:

MC = MD x .
( =
3.142).

### Example

What length of 10mm mild steel plate is needed to form a cylinder having
an outside diameter (OD) of 650mm?

Calculate the mean diameter

MD = OD - T

=
650 - 10

= 640

Calculate the mean circumference

MC = MD x =

=
640 x 3.142

=
2010.624mm

= 2011mm (rounded off to the nearest mm)

The following diagram shows the cutting length (mean circumference) of
the material.

Therefore a piece of 10mm mild steel plate, 2011mm long is required to
roll up to an outside diameter (OD) of 650mm and inside diameter (ID) of
630mm.