Ball
Slides
Load
Ratings and Life Estimates
The rated load capacity of Isotech ball slides
may be a mass load on a horizontal slide, or a force load normal
to mounting surface in any position. The rated load must be centered
and distributed over the slide, and the base must be fully supported
on a flat mounting surface so that the ball slide does not act
as a beam subject to concentrated or distributed bending forces.
Loads supported by protruding arms reduce accuracy and load capacity
by acting as levers or ratio arms, and should be avoided even
when load forces are small.
When used
at the rated load capacity and moderate speeds, a life of 10 million
inches of travel can be expected. The expected life at one half
the rated load is 100 million inches.
Friction
and Lubrication
The coefficient of friction is lower for linear
ball bearings than for rotary bearings, where the peripheral track
is shorter on the inner race than on the outer race, causing the
ball to skid on one or the other. The balls run exactly equal
distances on the pair of tracks in linear bearings, permitting
the balls to run without friction, wear, or skidding at any preload.
The typical coefficient of friction for Isotech ball slides is
.003.
Isotech ball
slides are lightly lubricated during assembly, and are self-cleaning
in normal service. Additional lubrication is required for speeds
above 1800 inches/min, and is advisable at lower speeds where
high loads are applied in continuous duty app lications.
Mounting
and Accuracy
The mounting surfaces of the ball slide are machined
flat and smooth, and parallel to each other and the line of motion.
They must be mounted on smooth, flat supports that will not deflect
under load. Especially with long slides of small cross section,
binding may be caused by distortion of the bottom member when
mounted on irregular surfaces. If so, round shims or spacers may
be placed over the mounting screws to raise the slide above the
surface asperities. Bedding in epoxy resin is also recommended.
The specified
accuracy for all standard Isotech ball slides is .0005 inch/inch
of travel. This is measured by comparison of the line of travel
to a master straight edge, using a gage or indicator mounted on
the slide.
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