Sky & Telescope - May 2021 - 72

ASTRONOMER'S WORKBENCH by Jerry Oltion

The Trolley Dob
This mount is about as simple as it gets.

mer and former physics teacher David
Newton became the proud owner of a
10-inch Sky-Watcher OTA. The original
owner kept the equatorial mount, leaving Dave with the scope still clamped
in its tube rings. As he considered his
options, Dave remembers thinking, " I
wanted to do something slightly different than the typical boxy Dobsonian
mount. In particular, I wanted to make
use of those handy tube rings if possible. My aim was portability. I wanted to
find out what the lightweight limit was
for a small, effective, rigid Dob mount. "
An old wooden bed frame became
available at about the same time, which
led to the obvious question: What
could he build with a bunch of long,
slender slats?
Dave says, " As the two tube rings
were attached to the dovetail bar by
two ¼-20 bolts, I made the assumption that the bolts would still take the
weight of the tube if placed on either
side and could therefore be used as the
altitude bearings. "
That led to a simple pair of triangles
reaching up from the base. In considering that base, Dave realized that if he
used the scope on a hard surface there
was no real need for a ground board.
So, he put three rollers underneath the
platform, aimed so they would roll most
easily in a circle. The rollers are called
" trolley wheels, " so of course Dave calls
the mount his " Trolley Dob. "
The upright arms started out relatively tall in order to put the eyepiece at
a comfortable standing height, but the
mount had quite a bit of flex, so Dave
cut it down and added cross-bracing.
That reduced the settling time to a
respectable one second or less and puts
the scope at a comfortable height to use
while seated.
72

M AY 2 0 2 1 * S K Y & T E L E S C O P E

X David Newton's
10-inch scope
awaits nightfall atop
its minimalist Trolley
Dob mount.

You might
think that with
its cross-braces
way down at the
bottom, those
long arms would
sway back and
forth even in
their shorter
incarnation,
but the tube isn't actually free-floating
on top. It's pinned tightly to the frame
with its tube ring and mounting bolts,
together acting as a rigid cross brace in
its own right.
Since the entire scope pivots in altitude on only those two ¼-inch bolts,
Dave needed to add friction to that
axis. He tried Teflon washers at fi rst,
but they were way too slippery. He then
tested steel washers of various diameters before fi nally settling on 120-grit
emery paper. That provided just the

The parts are as
simple as the
finished product.

right amount of friction, which he can
easily fi ne-tune by turning the knobs
(custom made by Georgia Stamps) that
tighten or loosen the bolts. He can
remedy any imbalance in the scope
by simply sliding the OTA up or down
within its single tube ring.
The mount's base was initially
rectangular, but Dave soon learned that
he was catching the corners on things
- especially his shins! - so he rounded
the front end, which not only eliminated the shin-banging problem, but as

DAVID NE W TON (2)

LAST SPRING, UK amateur astrono-



Sky & Telescope - May 2021

Table of Contents for the Digital Edition of Sky & Telescope - May 2021

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