Drive belt tensioner.

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My belt and braces construction must provide incredibly solid support for the worm by any normal standards. It seems to have taken some time to get this far but the journey was interesting. With several detours until the scrap metal, 70mm square, box section turned up on cue.

I think the result looks quite purposeful. An end cap on the motor sleeve might finish it off neatly. I have yet to discover if the motor needs more ventilation in use. The motor power socket entry slot reveals most of one side of the motor. Only time will tell if the motor needs more air to circulate around it. A computer fan in the end plate is another option.

I tried reducing the diameter of a scrap of 10mm alloy to see what size was needed for belt tensioning. An extended bolt for the nearest motor fixing will provide a suitable pivot. It is possible to buy new timing belts with 1 tooth less. This would avoid the need for a tensioner but make pulley fitting [with the belt in place] more difficult. It is probably kinder to the belt to fit a tension roller.

Then I discovered that it is far easier to withdraw the worm on its shaft from the housing. Only pushing it back through the pulley once the belt and pulleys are properly arranged. It is almost effortless to assemble it this way. See image right for a trial pulley. The urethane bush not quite large enough to properly tension the belt. I shall have turn something in the lathe tomorrow. It wants to be somewhere in size between the alu. disk and the rubber bush. Pushing the belt on the free side is a better indicator of tension than on the tensioner side.

The lesson for today is that belt tension is only measurable once the system is assembled. Trying to stretch the belt by adding pulleys during assembly doesn't work. Withdrawing the worm shaft to add the large pulley works wonders. The tension applied by the original alu. disk was fine. I don't think a rimmed pulley is necessary in so short a drive. The image shows the RA drive and wormwheel assembled on the mounting.

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Now I have to do much the same, all over again, for the Declination drive system. Though the worm housing is somewhat narrower and uses a smaller 8.5" wormwheel.

Click on any image for an enlargement.

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