Clutch Operation
Fig.1
CLUTCH OPERATION - The clutch knobs are shown in Fig.1. These do not have to be tightened super tight. Good and snug is all that's required to keep the axis from slipping. During use, when the knob is loose, the Ra or Dec can be rotated even though the worms are still engaged. In fact, unless you move the worm block away from the gear, the worm is always in mesh with the gear.
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Fig.2 |
Fig.3 |
The reason these axes can be rotated with the knob loose is that plastic piece sandwiched in between the upper and lower assemblies. See Fig.2 & Fig.3. The lower assembly is the part that contains the worm and gear. The upper assembly is the part that has the Ra or Dec stuff. With the clutch knob loose, the upper assembly can slip on the plastic piece. The plastic piece acts as a bearing. If it weren't there, you would have aluminum rubbing against aluminum, and that would be bad. The surfaces would eventually gall. When you snug the clutch knob, you are clamping the upper assembly to the lower assembly and when the worm turns the gear the whole assembly rotates.
Let's look at the Ra axis. With the clutch knob loose, the weight of the entire Dec assembly including the telescope assembly, and counterbalance weights imposes a huge load through that plastic bearing. So with the knob loose, and you rotate the assembly, friction at the plastic bearing caused by things like coefficient of friction of the materials, surface finish of the rubbing components, etc., create some drag or resistance to rotation. This is why some people do their balancing with the worm disengaged. With it disengaged, the assembly can rotate on the internal steel bearings which are very free wheeling.
