SECTION 5 - ROTATION MECHANISMS
A. Types. There are several types of rotation mechanisms found on Fresnel
lenses--carriage (chariot) wheels, ball bearing, and mercury-float types. Even
within these categories, they are not all alike, depending on the manufacturer
and the year they were constructed. As with any industry, every year a new
model came out and design improvements were made. NOTE: Power shall
be secured when servicing the drive mechanism to prevent personnel and
cleaning materials from being caught or crushed by the mechanism.
1. The carriage type of rotation mechanism (Figure 5-1) consists of large
bronze wheels riding on an upper and lower bearing surface known as a
road. In conjunction with the large wheels are small guide wheels around
the shaft of the pedestal assisting in the stability of the rotating lens by
preventing an orbiting motion of the lens. The wheels are all attached to
steel shafts by a pin or nut, and several washers were installed for radial
alignment of the wheels. The wheels have oil ports where a small amount
of clock oil can be inserted on a quarterly or more frequent basis. An
alternative to clock oil is non-detergent 30W motor oil. It is very important
to keep the road clean and free of debris so the rollers can rotate freely
and prevent them from being wedged and dragged around the road
causing flat spots. Excess oil should be cleaned off the roads and wheels
as it will attract dust and dirt that will increase wear on the mechanism.
Guide
Wheels or
Rollers
Figure 5-1. Carriage Mechanism
2. Ball-bearing rotation mechanisms (Figure 5-2) usually have a dust guard
installed and are easily maintained. As mentioned above, light oil is
required for lubrication purposes but care is required when lubricating
because the ball bearings ride in a machined grove called a "road". The
groove in the road also acts as the reservoir for the lubricant and if
overfilled will force out oil, making a mess and a safety hazard when it
runs onto the floor. Check the aid file to determine if specific oil is
5-1
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