Re: Maximum SAFE shimming thickness under a DOVELM162 clamp set ?

Christopher Erickson

Your truss tubes may not be glued but the ones on VYSOS-20 certainly are.
The gray epoxy is clearly-exposed on the ends. All of the truss connectors
have the small set screw that you mentioned as well. I suspect that the
screws were to hold the parts in place while the glue was setting up. The
truss ends may be a good place for you to investigate.

Christopher Erickson
Consulting Engineer
Summit Kinetics
Waikoloa, HI 96738

-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...]
Sent: Friday, September 19, 2014 1:25 PM
To: ap-gto@...
Subject: Re: [ap-gto] Maximum SAFE shimming thickness under a DOVELM162
clamp set ?

Thanks Chris,

...for the added info on the observatory's RC-20. I still suspect UPS
handling of the truss in its shipping container may have caused the DEC
orthogonality problem. The truss sat horizontally, rested on its saddle
plate, the entire truck ride across the entire USA. When it was dropped, the

truss cage could have shifted - the entire secondary and baffle flew off at
some point, and I found it rolling around the crate - for ho knows how long.

So, it was a rough passage. Luckily, Paul Jones rework, was far better than
the original mirror figures. But I suspect a truss stretch, even though I
didn't see any damage. The truss would have to have been travelling very
fast downward, to whip the secondary off its mount.

No matter - all came out perfect in the end.

Since my last post, I managed to bring the original RA meridian flip
coordinate shift down from a horrible 28 arc-minutes to just 0.5
arc-minutes (measured at the equator), but the DEC after a flip is still off

by 5.5 arc-minutes, which is not too shabby, considering where I started
from. I got to this point by adding a couple of measured thickness brass
shims for the DEC orthogonality error - just as Roland said it was - and
probably well over a dozen runs of PemPro polar align wizard, tweaking down
the Az-Alt adjusters by infinitesimal movements.

Thanks again to "Richard Moore", who recently posted his instructions
for easily "slipping in a shim under a scope", without actually taking down
the 14-inch OTA. Adding shims and testing successive thicknesses, was a pure


I wonder, if even that 5 arc-minutes DEC coordinate error might even be
a tiny discrepancy of my actual observatory GPS coordinates. Those provided
by the GPS feature of my Olympus camera (and also Google Maps icon, set to
my driveway), are about 5 arc-minutes different in Latitude from general
tourist website published GPS coordinates, of the downtown city centre -
just 3 km. away. So, which one is closer to being correct - trust the simple

camera, Google, or a government website?

I am going to try to fiddle the setting in the ASCOM driver setup table,

and in the Planetarium program, by these 5-arc-minutes, to see if they
suddenly line up with a patiently well polar aligned AP-900. That would be a

surprise. PemPro polar align wizard should have nothing to do with my
observatory coordinates - even though I see that one of the run screens has
it displayed. Perhaps that is just user information downloaded from the
mount, only for reference. Don't see PA needing my coordinates to do a
proper job - just "redundant" screen information.

So, I am finally satisfied with the now consistent results from the
shimming, and many, many polar alignment runs.
A happy astro-camper at very long last.

You said that the RCOS TRUSS tubes are "glued in place" ? Are you
certain of that?
I suspected it but I see no mention of it anywhere. There is, however, a
very tiny set screw, in every truss pole, pinning it to the boot at each
end. Don't know if it was to initially position each pole as the glue set,
or if it is the ONLY thing holding it in place. Replacing a damaged pole
would be a bear if it had to be chipped out of any glue or epoxy in the


Posted by: "Joseph Zeglinski" <J.Zeglinski@...>

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