Timber skids (planks) are placed longitudinally
under heavy loads to distribute the weight over a
greater area. (See fig. 6-35.) The angle of the skids
must be kept low to prevent the load from drifting or
getting out of control. Skids can be greased only when
horizontal movement is involved. Extreme care must
be exercised. In most circumstances greasing is
inherently dangerous, as it can cause the load to drift
sideways suddenly, causing injuries to personnel and
damage to equipment.
Hardwood or pipe rollers can be used in
conjunction with plank skids for moving heavy loads
into position. Planks are placed under the rollers to
provide a smooth continuous surface to enable them
to roll easily. The rollers must be smooth and round to
aid in the ease of movement and long enough to pass
completely under the load. The load should be
supported by longitudinal wooden members to
provide a smooth upper surface for the rollers to roll
on. The skids placed underneath must form continuous
support. Normal practice is to place four to six rollers
under the load to be moved. Several rollers are to be
placed in front of the load and the load is then slowly
rolled onto these rollers. As the load passes the rollers
that are left clear of the load they are then picked up
and moved in front of the load. This creates a
continuous path of rollers. Turns can be made using
rollers; but, first the front rollers must be inclined
slightly in the direction of the turn and the rear of the
rollers in the opposite direction. This inclination of the
rollers can be made by striking them sharply with a
sledge hammer. Rollers can be fabricated and set on
axles in side beams as a semipermanent conveyor for
lighter loads. Permanent metal roller conveyors are
available (fig. 6-36) and are normally fabricated in
sections which can be joined together.
BLOCKING AND CRIBBING
Block timbers are commonly used to provide a
foundation for heavy loads or jacks. Cribbing must be
used when a heavy weight must be supported at a
height greater than blocking can provide. Cribbing is
made up by aligning timber in tiers that run in alternate
directions (fig. 6-37). Blocking and cribbing is often
necessary as a safety measure to keep an object
stationary to prevent accidents and injury to personnel
working near these heavy objects.
When selecting blocking as a foundation for jacks,
ensure it is sound and large enough to support the load
safely. It must be free from grease and thoroughly dry.
Figure 6-36.Permanent metal roller conveyor.
Figure 6-37.Examples of the use of cribbing.
Additionally, it must be placed firmly on the ground
with the load (pressure) distributed evenly.
A firm and level foundation is a paramount
requirement where cribbing is used. Also, equally as