Re: Can't remove counterweight shaft

Don Anderson

Stainless steel is a great metal but its down side is its tendency to gall in moving metal to metal part. All things considered, I agree with you the Teflon washer is the cheapest, least complicated and cleanest option and would likely work just fine especially in portable setups.

--- In ap-gto@..., "Joseph Zeglinski" <J.Zeglinski@...> wrote:

Hi Don,

I see your point. However, the Teflon washer would get depressed at ALL
points, eventually. As the RA axle turns during operation, the washer is
depressed, at various times and positions, a full 180 degrees around its
circumference. So, half of a soft Teflon washer may potentially get somewhat
thinner. But, if we are discussing a shaft that is removed regularly, the
rotational position of the "loose Teflon washer" will change with each shaft
attachment, so the washer will eventually undergo a full 360 degree range of
compressions. Thus there should not be a problem of an unevenly compressed
Teflon washer. Those with permanent observatory use, would not require the
washer at all.

To overcome the possibility of uneven Teflon washer wear as you
describe, one other approach I might consider, though it takes a bit more
work at the factory, is to add some "dimples" (maybe 5) to the aluminum
housing ring. Drill and tap 5 holes and insert 5 round head steel pins, or
plugs if you will. The shaft should lock down tight, but bear "upon the
tips" of the 5 pins. This presents a firm "steel upon steel" bearing, with
easier slip than the flat, softer aluminum mating surface of the ring
itself. Stiction is avoided since the surface is no longer flat, and the
contact area is no longer the annulus but rather limited to 5 small points.
The steel bar should then glide easily into or out of contact, and the wear
or indentation is minimized by the hardness of steel pins bearing on the
steel shaft.

In fact, either 5 holes can be drilled and plugged with round pins, as I
described - or alternatively, a 5 hole ring with rearward inserted "steel
ball bearings" could be screwed to the bottom of the aluminum DEC ring. Thus
the shaft would finally bear onto a ring of 5 steel balls. It would not be
difficult to manufacture the retaining ring for those steel balls.

However, this solution, at the risk of ruining one's own aluminum lock
ring, is beyond the skill of most people to implement on their own, and thus
should be left as an AP "optional retrofit" part to exchange in the field
with the existing aluminum base ring (with its factory return, to drill &
tap for other kits). Cost of this retrofit part should not be considerable,
and future mounts could incorporate it directly.

The question remains, however, if this "high point" contact is
sufficient to assure a permanent lock down, or whether with the lack of
stiction, the shaft could begin to unscrew itself (somewhat), if depressed
as in the #2 and #3 positions. In fact those are extreme positions, and the
shaft thread is potentially always under a thread sag condition, at almost
any RA position.

All things considered, a Teflon washer, or a Teflon coated Steel washer
to minimize the possibility of Teflon softening, is the simplest and
cheapest 2 cent solution, worthy of field trials.

Interesting discussion, Don. You have a lot of good thoughts on the matter.


----- Original Message -----
From: "Don" <jockey_ca@...>
To: <ap-gto@...>
Sent: Sunday, April 04, 2010 12:28 AM
Subject: [ap-gto] Re: Can't remove counterweight shaft

Hi Joe
I have thought of the teflon washer option as well and I believe it would
solve the stiction problem. On thing we have to keep in mind though is the
two flat mating surfaces on the shaft and housing adapter are what keeps
the shaft straight. If we add a washer that is too soft and can not stand
up to the lateral loading of the counterweights, one could end up
stretching the threads in the aluminum Dec housing adapter. a Teflon
washer should work if the mount is disassembled after each night. I would
be concerned if the mount is left in one spot especially something like
Park 1 position for an extended period of time one could get creep in the
low side of the washer and unduly stress the adapter threads.
Just a thought

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