4.5 Declination Axles
The declination axles are made of three pieces.
The
inner bearing of the fork is a 4" I. D. ball bearing and the outer
bearing
is 60mm I. D. bearing. This arrangement allowed the use of a less
expensive
outer bearing and provided more room for a tangent arm. The declination
axle required a step form 4" to 60 mm. I turned a piece 4" long piece
of
4" 1/2" wall aluminum tubing so that I had a recess to put a turned
0.500"
disk of aluminum plate to act as a reducer for the 60 mm tubing. The
60mm
tubing is used for the rest of the axle which is about 9" long. The
60mm
tubing is pressed into the 0.500" disk. The three pieces were welded
together
and machined to the proper dimensions for the declination axle
bearings,
Figure 4.5.1.
Figure 4.5.1 The declination axle as seen from inside the telescope fork. The 4" inner bearing can be seen in its bore.The Declination bearing is not sealed. The outer portion of the bearing needed a grease seal to protect the bearing from the environment. Two problems needed to be solved concerning the grease seal, 1) a 4" greases seal is expensive, 2) such a grease seal is thicker than the room that I had. A simple solution presented itself. Many years ago, before modern seals were made felt was used as grease seals. I decided that I could do the same for the dec bearing. I machined a small recess around the bearing bore 1/8" deep. Felt was cut the diameter of the recess with a hole 1/2" smaller in diameter than the shaft. When the felt is slipped over the dec shaft it forms a seal around the shaft, Figure 4.5.2.
Figure 4.5.2, The dec shaft grease seal is made felt. this technique has been used for years to protect bearings from dirt.
The mounting flange and bolts can also been seen in this image.
A small thin ring was machined to hold the felt in place and
cover
the bearing, Figure 4.5.3.
Figure 4.5.3. The felt retainer ring was machined to fit over the felt. A hole of sufficient size was left in the retainer to allow the felt to form a seal around the dec shaft.