Meade LX200GPS 8" (Fork arm adjustment)
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The individual arms need to be matched to the machining of the RA base to which the attach.
It is most likely that the RA axis, which is determined by the machining of the RA bearing carriers, is not aligned to the fork arm mounting face. This needs to be corrected. The error has to be measured with the fork arms attached to the RA assembly. Then with the arms removed to enable the angle of the mounting face to be adjusted.
The required angle is determined for each fork arm individually, such that when assembled the arms are parallel to each other and to the RA axis.
Prior to the OTA being fitted the arms should be out of parallel with each other. This is necessary to apply a preload to the DEC bearings. The amount of pinch on the OTA should be determined for each individual case. If the DEC bearings have been shimmed to give zero end float plus preload, then the OTA pinch is not of great importance and a nominal 0.020" (0.5mm) pinch is recommended.
However if the bearings are not shimmed on both forks, then a preload pinch, equal to the weight of the OTA plus accessories, must be applied if Polar Alignment is to be used.
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All photographs a copyright of Conrad Maloney (CRCM Networks, United Kingdom)