Our intention is to help bushing users by providing information from our years of
experience with bushing applications. Due to a wide variety of applications and unique
operating conditions we cannot be responsible for any recommendations made in this
section.
Bearing Construction
One very critical aspect in the design of a machine tool is the proper choice of a
rotary bushing or toolholder. Gatco designs and manufactures rotary bushings and
toolholders for specific operations. During the design phase it is very important to
choose the proper bearing construction for a particular application. As an example, line
bore bushings require a very high degree of accuracy, therefore the bushing needs to
incorporate class 7 or 9 angular contact bearings for precision runout. Milling operations
do not require precision runout, but do require bearing construction that is durable and
will accept heavy radial loads as well as shock loads, normally tapered roller bearing
construction is recommended for this application. As demonstrated in the above examples it
is very important to choose the correct bearing construction for the bushing or toolholder
to be used. If you have questions as to what type of bearing construction is recommended
for your operation contact Gatco’s engineering department.
Seals
The method of sealing a rotary bushing or toolholder is very important. Consideration
must be given to the environment in which the product will be operating. Seal selection is
made based on many factors such as, coolants being used, the material being machined,
whether the chip is coarse or fine and temperature considerations. Also a very important
factor, is choosing the correct sealing element which will hold up and not deteriorate
when certain coolants are used. Quite often due to high speed operation contact seals
cannot be used due to the friction they create, in these cases non contact seals must be
considered.
Alignment
One of the most common causes of pre-mature failure of virtually any bushing or
toolholder is caused by mis-alignment between the spindle or toolholder and the bushing.
Mis-alignment causes excessive radial loads causing friction heat and wear. Although the
anti-friction bearings will accept a tremendous amount of radial load, if the
mis-alignment is to great pre-mature failure will occur.
Lubrication
Satisfactory rotary bushing and toolholder performance is dependent upon good lubricants
and correct lubrication practices. Most rotary bushings and toolholders will not require
re-lubrication because the operation is not severe, but a lube provision is provided for
re-lubrication if necessary. The lubricant performs the following important functions:
| 1) |
Forms a film between the rolling element and
raceways and between the rolling element and the cage or retainer thereby minimizing
friction and wear. |
| 2) |
Protects the bearing surfaces against
corrosion. |
| 3) |
Dissipates heat generated by the bearing when
operating under load. |
| 4) |
Acts as a seal to limit the infiltration of
contamination into the rotary bushing or toolholder. |
| 5) |
Lack of lubrication or excessive lubrication
will cause heat and premature failure of the rotary bushing or toolholder. |
Temperature
The operating temperature of a rotary bushing or toolholder results from the friction
from the bearings, seals and, possibly from extraneous sources as well as heat dissipation
from the adjacent components. Excluding extraneous heat, the operating temperature of a
rolling bearing at medium speed and load is not high because the bearing friction is
small.
In typical machine tool operations temperature
is not a problem due to the slower speeds at which the machine operates. In situations
where high speeds are encountered or increased temperature is anticipated consideration
must be given to lowering the operating temperature. Quite often temperature can be
lowered by incorporating non contact seals or connecting the bushing to an automatic oil
lube system. If temperature rise is encountered contact Gatco’s engineering
department for assistance.
Load Capacity
Rotary bushings and toolholders can accept very high radial loads. Most series can
also accept high thrust loads. Bearing capacities are normally considerably higher
than any load that would be generated in a machine tool application. Refer to the speed
and load tables for limitations. If your operation exceeds the load limitation on a
particular bushing or toolholder contact Gatco’s engineering department.
