Copyright Jack Russell 2012
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The AstroBaby tutorials are an amazing piece of work, but I believe you can improve on these procedures in a two key areas to make the mount perform optimally.
First of all, the worm bearing tension, set by those horrid threaded slotted circlips, should be set before you fit the worm housings to the mount. Fit the pulley-side end cap fully, then spin the worm by hand and tighten the adjustable circlip with your circlip pliers until you feel it just start to generate resistance as the worm rotates. At this point you will have no float, but the worm rotation should still be smooth, without binding.
If you leave these loose until after rebuild, you will then have 2 variables affecting backlash - worm/ring gear engagement and worm bearing end float, not helpful.
The worm to ring gear meshing is not easy to set perfectly. Juggling those two hex set screws takes time, and sometimes a bit of trial and error.
First off, try to make sure that the entire worm housing is square. Compare the 4 sides of the housing with those of the main body of the mount and try to get this straight as you initially tighten the set screws. Adjust the 2 set screws to start with to deliberately achieve about a small amount of backlash in the axis you are adjusting. At this point make sure the 4 bolts securing the worm housing are just secure but not tight.
Then, slip a short piece of 10mm hose over the end of the worm which sticks out proud of the circlip (I used a tie-wrap to make it grip properly). At this point you should be able to spin the worm easily by rotating the hose (your motors should not be fitted yet of course).
Gradually increase the engagement adjusting both small set screws (one to tighten, one which fights it) until the hose slips on the worm (rather than turning it). At this point the worm is binding on the ring gear. Then back off the set screw which pulls the worm housing, and therefore the worm, onto the ring gear, by about 1/16 of a turn.
Now see if you can turn the worm again. Keep adjusting until you can spin the worm with the hose without binding. You should then have the least backlash possible without binding of the gears. Keep tension on both set screws, so that tightening or backing off one by just a fraction generates slight movement of the housing (and worm).
If you still have gears in your mount - Unlucky. Changing the worm engagement means moving the worm housing, which means changing the mesh between the transfer gear and the one on the worm. This may then mean you have to reset your motor pinion engagement.
The best thing about the belt conversion is that you can now adjust worm to ring engagement without creating binding in your motor pinion/transfer gear train, and tension the belt without affecting worm engagement.
I’ll add some pictures soon to show this a bit better, but hopefully the text will be fairly self explanatory.
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