IV. Mounting

4.6 Mount Base

After the completion the polar axle a mounting for the polar axle needed to be designed. My original design was to mount a roller bearing assembly on two 4' x 5" tubing with the south polar axis bearing recessed in the base. This arrangement did not allow the fork to clear the ground and the tubing proved to be to light for the weight of the fork and polar axis. The entire mount base had to be redesigned.

The final design consisted of two pyramids made of 0.500" aluminum plate. The front face of the pyramids are made of a single piece of 0.500" plate. The front face of the pyramid is angled at 400. The apexes of the pyramids are canted back to accept the north polar axis roller assemblies, Figure 4.6.1a and b. The south polar axis pillow block bearings is bolted to a 0.500" plate.

a  b

Figure 4.6.1. A front and rear view of the mounting base. The roller assemblies where the disk rest and rolls on are mounted on the pyramids with 1/2" stainless bolts. The south polar bearing is supported on a plate that is supported by two gussets.

 The south polar axle bearing plate has two gussets for supporting the load of the polar axle and holding the plate at 400 so that it is parallel to the north plate. The pillow block is self aligning which reduces the need for accuracy in welding the south polar axle bearing plate parallel to the north polar axis rollers, Figure 4.6.2.

Figure 4.6.2. The south polar axis bearing and cap.

 The roller assembly that replaces the north polar bearing consists of 2 self aligning roller assemblies. Each assembly contains 4 trucks of 2 bearing pairs, situated in 2 small rocker assemblies. The 2 small rocker assemblies are mounted in a larger rocker that is mounted to the pyramid base so that the rollers are self aligning, Figure 4.6.3 a  b

Figure 4.6.3. Rocker bearing assemblies on the mount base and south polar axis bearing. The rocker assemblies provide self alignment with the polar axis disk. The disk rolls on a total of 64 bearings.

 Each rocker assembly has 32 bearings. The roller assemblies provide a total of 64 bearings for the 26" disk to roll on. The bearings are automotive alternator bearings that were provided by a local alternator repair shop. The bearings in an alternator are replaced no matter what shape the bearing is in when the alternator is rebuilt. I got a large box of discarded bearings for free. I picked out the good ones for the project.

The mount base is mounted on an "A" frame, Figure 4.6.4a. The base assembly is made so that it can pivot in azimuth around a bearing that is at the front of an "A" frame. Figure 4.6.4b.

a  b

Figure 4.6.4. The mount base on the A frame 4.6.4a.. Figure 4.6.4b shows the front pivot bearing. This bearing is also a pillow block so that the bearing can move as the mount base moves in altitude and azimuth.

 The back of the mount base has a cross slide form a lathe for adjusting the mount in azimuth. I machined off the dovetail portion of the cross slide so that the lathe slide could be bolted to the "A" frame base. An adapter plate was machined so that the altitude adjustment jack and pivot bearing could be mounted to the lathe cross slide, Figure 4.6.5a. The lathe cross slide, the connecting u-joint, and azimuth pivot bearing are shown in figure 4.6.5b. The azimuth pivot bearing allows the altitude jack to pivot when the azimuth cross slide moves. a  b

Figure 4.6.5. A lathe cross slide was modified and used to move the mount base in azimuth, figure 4.6.5a. A small DC motor and gear system is used to connect the motor to the lathe cross slide, figure 4.6.5b.

 A small DC gear head motor drives the mount base in azimuth. The motor is connected to a small four start worm drive. The motor assembly is mounted at an angle relative to the cross slide so that a u-joint is necessary to connect the worm drive to the cross slide. Figure 4.6.6 shows the motor assembly on the A frame.

Figure 4.6.6. The azimuth motion is controlled by a DC motor. A 4 start worm gear is connected to the lathe cross slide by a u-joint. A DC motor drives the telescope in azimuth for polar alignment.

 The altitude adjustment is a screw jack arrangement that is mounted on the rear of the mount base, Figure 4.6.7a. The mount base can be raised and lowered with the screw jack. A motor is mounted through several sets of gears shown in Figure 4.6.7b. a  b

Figure 4.6.7. The mount base is mounted on an "A" frame that allows the entire telescope to be moved in altitude and azimuth for polar alignment.

 The Alt and Az adjustments are both motorized for ease in polar alignment. Two switches are on a long cable so that the alignment can be done at the telescope eyepiece. The telescope is far too heavy for the usual "kicking the tripod" method of alignment. Kicking this mount only results in a busted foot!

The fork and polar axis placed on the mount base, Figure 4.6.8. The welded areas can be seen as bright areas on the fork. (Note that the outer sections of the fork are made of 4 pieces of plate.) The box tubing that was used to fabricate the base can be seen in the fore ground. Caps were welded into the open ends of the box tube for completeness.

Figure 4.6.8. Completed fork mounted on the mount base as seen from the south polar bearing. This is a the first time the fork was set into place on the mount base. The mount base had not been completed.

 The mount base is designed so that it could removed from the "A" frame and mounted in an observatory. If I ever get that fortunate.

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