On Apr 26, 7:37*am, Davoud wrote:
I have installed a RoboFocus on my FSQ-106ED in a manner that is
different to what I have seen before, and, I think, considerably
sturdier than most other methods. The method I used may be applicable
to other refractors as well.

Are you brave enough to drill some holes in your 'scope!? :)

Please see http://www.primordial-light.com/fsq-robofocus.html.

Davoud

A beautifully illustrated modification but I would have started with a
much smaller drill and worked upwards in diameter. (not necessarily
drilling very deep with each drill in turn because smaller drills are
far more prone to "wander" in deep holes)

It is very difficult indeed to start a drill (of the size shown)
accurately in a centre-punched dimple. The width of the chisel point
of the drill is much greater in that size than the width of the
punched dimple you are using to try and start the drill accurately.

Pencil marking is also fraught with difficulty when working to fine
limits in metal. The width of a pencil mark is often too wide for fine
marking out. A scriber (using very short lines to avoid cosmetic
damage) is safer. The marks can be examined with a magnifying glass
before centre punching and drilling even begin. "Measure twice (or
several times) cut only once."

" Spotting" through the holes of the object being attached can be a
much safer option if the item can be clamped very accurately (and
immovably) in place first. A sharpened steel rod (known as a transfer
punch) which fits the fixing holes perfectly without any slop (at all)
can be used as an accurate centre punch to mark the metal below. The
point on the rod would have to be reasonably concentric (or the
marking punch rotated) to ensure accuracy. This is also possible by
filing or using an angle grinder while the rod is spun in an electric
drill on a drill stand. Once marked with a sharp point by the
transfer punch the small dimple must be further improved with a proper
centre punch. This is to achieve a flatter 90 degree total angle
dimple suitable for starting a drill.

Sighting through the holes of the object to be attached is a good idea
before work starts to ensure one is not drilling in the wrong place.
The spots left by the punch can be checked for exact concentricity
with the fixing holes by laying the object exactly over its intended
position.

Actually drilling through the fixing holes (of an object to be
attached) is likely to be much less accurate than using a transfer
punch. The drill tries to move sideways under cutting loads even if
the drill starts as an accurate fit in the fixing holes. The hole in
the base metal will also be considerably oversized if you want to
thread the holes in the base metal. There will be no metal left to
take a thread if you drill with the same sized drill which matches the
fixing holes. The hole in the base metal must be considerably smaller
to give you some metal left to cut a thread.

You are certainly a very brave chap for attacking such expensive gear.
Even if the end result was highly desirable and proved successful.