Worm support metalwork: PA spacer sleeve and top bearing cap.

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The new worm housing required a 10mm spacing between the wormwheel boss and the top PA bearing. So I decided to use some of my latest, scrap aluminium bar to make a stepped sleeve to enclose the top bearing. This would provide a solid 10mm spacer and hide the potentially rusty, steel bearing sleeve. It would also make the short gap above the top bearing look more like a much larger PA shaft.

First I bored the bar right through to 50mm diameter to match the polar axis shaft. Then I reversed the blank in the internal jaws of the 3-jaw chuck to bore the 62mm clearance diameter for the bearing. Then I turned away the excess material until the worm perfectly matched the height of the wormwheel above the main support plate.



Then back to the internal jaws to turn the outside of the sleeve smooth and take off all the sharp, turned edges.

The image shows the sleeve in place on the polar axis below the wormwheel boss. Since the sleeve rotates with the wormwheel there is no need to provide a low friction bearing between them.

All slews will be via the AWR drive system with the  clutch effectively almost solid. The clutch has now shifted from relying on the radial nylon plugs in the wormwheel boss. The 7" diameter disk of PTFE between the cylinder and the 11" wormwheel will be loaded by the OTA and Declination assembly. If friction proves to be too high I shall have to increase the load on the lower PA bearing. Or make a pressure plate to allow a screw to push the PA shaft upwards for clutch pressure adjustment.

Click on any image for an enlargement.

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