Sky & Telescope - December 2023 - 62

Customization
placed at an awkward angle. It stuck
upward at a 45° angle, which meant that
when the scope wasn't aimed straight up,
Dan had to get above it and look down.
That largely negated the advantage of the
scope's short focal length, so Dan and I
rotated the cage so the focuser was horizontal.
That meant fabricating new truss
mounts, but that turned out to be easily
accomplished with short sections of angle
iron. We had to work up our courage to
drill through the thin box tubing of the
secondary cage ring, but we used small
bolts and left plenty of metal for strength.
And now Dan's focuser sticks out horizontally
no matter where the scope is pointed,
and he doesn't need a ladder.
Dan's scope required several additional modifications - as
he says, " Many of them involving Loctite. " One memorable
night as he was setting up after a long drive over washboardy
gravel roads, his scope's secondary mirror simply fell off in
his hand as he was collimating it. The set screws holding
it in place had all rattled loose! Several other bolts on the
scope had also loosened up, so he fixed them all in place with
thread-locking adhesive.
The rivets on Dan's telescope mirror box scraped against
the side struts of the rocker box, so he put plastic skid plates in
place to keep them from hitting. The altitude-bearing surfaces
also needed to be replaced with Teflon in order to equalize the
force required to move the scope in altitude and azimuth.
Sometimes it's the other way around, and the scope is
stiffer in azimuth than altitude. Fortunately, that's an easy
fix. First try loosening the nut on the pivot bolt that holds
the rocker box to the ground board. If that doesn't fix it,
then take the bolt out and put a stack of washers between
NEEDS IMPROVEMENT The collimation
adjustment screws on this scope are crying out for
a set of Bob's Knobs. You shouldn't need both a
Phillips screwdriver and a hex wrench to collimate
your mirrors.
the two boards. The washers will take
some of the telescope's weight, reducing
the load on the Teflon pads out near the
perimeter, and the scope will move more
freely. You'll have to experiment with
the number and thickness of the washers
until you get just the right feel, but you
can fine-tune until the effort to move the
scope in azimuth matches the effort to
move it in altitude.
Eliminating Tools
Often a scope that's designed to be assembled and disassembled
on-site will come with small bolts that require wrenches.
You can make setup and tear-down much easier by using larger
bolts with more easily gripped heads. My fix is to get a longer
bolt, spin a couple of extra nuts up against the bolt head, and
cover the nuts with a length of rubber hose (available at just
about any hardware store). That lets me tighten and loosen
them with just my fingers - no tools required.
There's a company called Bob's Knobs (bobsknobs.com),
started in 1999 by Bob Morrow, that sells replacement knobs
for the collimation screws in Schmidt-Cassegrain telescopes.
It's the same concept: With Bob's Knobs you can use your
fingers, rather than a hex wrench or a screwdriver, to make the
fine adjustments required for collimation. This modification
isn't just for Schmidt-Cassegrains, either: You can also replace
the collimation screws on the back of Newtonian scopes. Bob
has since branched out with custom knobs for many other
applications, so check his website for ideas as well as materials.
SMOOTH TRACKING Teflon altitude bearings made the scope move
much more smoothly.
62 DECEMBER 2023 * SKY & TELESCOPE
SCRAPE GUIDE Skid plates keep mirror-box rivets from banging into
rocker-box struts.
http://www.bobsknobs.com
Sky & Telescope - December 2023

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