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14
OPERATION OF THE MOUNTING
R.A. and Dec. Damper Knobs
The R.A. and Dec. damper knobs are not intended as axis locks. They should be tightened with light finger pressure so that
a slight resistance can be felt when pushing an unclutched axis by hand. This really adds to the "feel" at the end of the
scope with the drives adjusted correctly.
The purpose of the damper knob is to add a bit of friction to the shaft so that gusty winds do not move the axes in their
bearings. If there is the slightest amount of backlash between worm and worm wheel, a wind load could theoretically move
the axis back and forth by that backlash amount. Also, in the absence of backlash, there is always a very tiny clearance
(.0002") between the shafts and the mating parts. The damper knobs force the shaft to make full contact in 3 places to
eliminate the associated play.
R.A. and Dec. Clutch Knobs
1. What do they do?
The four R.A. and four Dec. clutch knobs depicted in Diagram 2 have the function of connecting the R.A. and Dec.
axes to their respective drive worm wheel gears. Their function is progressive, from no tension (axes free to move
- as required during correct balancing of the telescope) to a completely "locked up" state.
2. How can you find out what they really do?
As shipped, all 1200 mounts have all four R.A. and Dec. clutch knobs firmly hand tightened. This will give you a
good idea of the maximum tightness (clutch action) that can be achieved by hand effort alone. At this point, you
must bear in mind that for optimum performance all four clutch knobs on each axis (R.A. or Dec.) should be
tightened evenly with the same tension i.e. all four half tight, all four fully tight, etc.
In order to feel the effect of the clutch knobs, you may wish to partially assemble your mount. Fit together the R.A.
and Dec. assemblies plus mounting plate and counterweight shaft. Do not put scope and counterweights on at
this stage. With the above assembly (with the clutch knobs firmly hand tightened - "as shipped"), you can feel the
amount of force needed to move each axis by hand. Grab each end of the telescope mounting plate and move it
with a backward and forward movement of the Dec. axis. You will feel considerable resistance to this motion.
Perform the same operation on the R.A. axis by moving the counterweight shaft backward and forward. With a
well balanced telescope, the above tightness of the clutch knobs will be sufficient for all normal conditions of use.
Now if you proceed to mount up and balance your telescope you can "feel" what this resistance in R.A. and Dec.
(movement backwards and forwards) is like when you make these motions from the eyepiece end of your
telescope as you would during normal use when slewing (pushing) by hand to acquire an astronomical object
within the field of view of your finder or scope.
3. How tight can the clutch be and can you do any damage by pushing against them?
The maximum tightness of this clutch system is 1/3 turn (with a 5/32 allen key) further in than the tension you can
achieve with the knobs by hand. You will see that each clutch knob has a 5/32 hex socket for tightening with an
allen key. With this extra 1/3 turn on each clutch knob, the axis (axes) will be considered completely "locked up"
and you should not attempt to push your scope by hand against this "locked up" resistance, or undue stress will
be placed on the worm wheel/worm and bearings.
However, if you are undertaking a very long astrophoto exposure, it is advisable to increase the pressure on each
clutch knob (with the 5/32 key) by about 1/8 turn on Dec. and 1/8th turn on R.A. You may safely slew the scope by
hand with this tension, however you will notice considerably more effort is required to achieve movement. This is
the absolute maximum tension that can be used for hand slewing. As a general rule, if you have a big scope (7" or
8" refractor) with all the accessories, you will need more clutch tension than a 5" or 6" scope.
Balancing Your Telescope
For proper operation, the telescope must be adequately counterbalanced. Start by balancing the tube assembly.
1. Tighten the 4 R.A. axis clutch knobs.
2. Loosen the 4 Dec. axis clutch knobs (about 3/4 to 1 turn) so that the telescope moves freely about the declination
axis (be careful because if your telescope is significantly out of balance, it may swing rapidly in the out-of-balance
direction!)