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Re: Yup its the 75 second cycle

 

Very nice work.
You have nicely demonstrated a faster and more consistent way to polish down the R4 bearing OD.??

As you say, you must always be very careful around any power tools.? We are in a hobby for fun, not for danger.? So care if the hands and eye protection, and a face mask to avoid inhaling dust are important precautions.?

That said, I have used my bargain priced Wen brand drill press to polish ODs down (on brass rods) before, so this is an accessible way of polishing small round items at rather low cost.? The drill press has no explicit cutting tool in it...just a round bearing.??

The only thing doing the cutting is an emery cloth or fine sandpaper.? (I like the 3M "wet or dry" paper because the grit is well embedded in a kind of string waterproof adhesive.? You can wet the paper to keep polishing dust down.? ). The sandpaper can get hot, but it generally won't cut you.??

The notion about extra benefits of allowing the bearing (at least the far bearing away from the gearbox) to self adjust it's angle in the worm block...these are new ideas.? We don't really yet know a "spec" on the best amount of OD slack to use.? Ideally you don't need any slack at all if all the parts are perfectly made.? Most people never see the 76 sec oscillation so never need this extra workmanship.??

A theory for the riddle:
? ? "why is a single Belleville washer under the (OD loose) far end bearing sufficient?? Why don't you need that spring under both bearings? "

An idea:?

Many people preload their RA axis with an intentional East bias. Say a weight on a cord, wrapped so the weight hangs to the East side of the RA axis.? We have discovered that the East bias eliminates a vibration ("chatter") that occurs if you bias to the West instead.??

When you preload the RA axis (ring gear) with an East bias, this forces the worm to move West.? That presses the worm against the West "far" end RA worm bearing center, and leaves the near (near the gearbox) bearing center looser.? So the West far worm bearing becomes the more critical surface for the RA drive: the worm is mostly rotating on that ball bearing race surface, not in the bearing closest to the gearbox.? ?That's why eliminating rumble of that far bearing becomes more critical for low noise sidereal tracking.??

This idea might explain why we see a reduction or elimination of the 76 sec oscillation when we reduce the OD (allowing tilt) and put a Belleville spring behind just the far worm bearing... the spring allows the bearing when tilted to still ride on a "self-leveling" seat.? ?

Otherwise, reduction of the 76 sec oscillation should only be effective some of the time...but it seems to be working all the time.? The East side bias effect could explain this riddle.?

By this reasoning, using a West side bias might create a 76 sec oscillation even with a Belleville spring under the far West bearing? ...there's another experiment to try!? ?

All the best,
Michael


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On Mon, Apr 5, 2021, 10:01 PM John Kmetz <jjkmetz54@...> wrote:
Alan/Michael/all:

Just tried the bearing spinning rig today with success. I placed the assembly in a drill press at 100 RPM and started trying small metal files and types of sandpaper to hone down the bearing. Surprisingly the outer race is fairly hard steel and doesn't shed diameter easily. Finally I used the corner of a sharpening stone, like that used for scissors or straight razors, and that was the trick. Subsequently I polished with 200 then 600 mesh sandpapers. It looks like reducing OD about 0.002" is the point where the bearing will begin to slide freely inside the block (see pics). The outside race also seemed to be virtually round and smooth after this process. Before pulling apart the rig, I sprayed away all the sanding dust with some WD-40 and then some compressed air. Upon finger turning the finished bearing I did not sense any hang up or grittiness inside.

Perhaps this is a new way for reducing the bearing OD to allow the Belville washer to do its thing. I found this a bit easier than turning down by hand. Perhaps a bit more OD reduction might be needed for those who wish some off axis tilt, but too much might start the bearing turning inside the block. But I think polishing down to 0.623" is the place to start. But just a note a caution for those who are not that familiar with moving machinery: the spinning drill assembly could easily cut the skin, or send particles into the unprotected eye. Use precautions.

Hope this info is of use.

John
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