Re: ATM Help with ALICE !

[Bob Scholtz <rscholtz@iquest.net>]

> > John Akers wrote:
> > >
> > > -- [ From: John Akers * EMC.Ver #2.5.02 ] --
> > >
> > > Chaps ! I'm building an 8" f 6 scope based on the scope like Alice. I'm
> > > using aluminium  box sections, for the main uprights (19mm box 2mm thick)
> > > which slide very snugly into 30 cm long guides which are fixed inside the
> > > mirror box, and on the focusing board (these are 25mm section box 3mm thick)
> > > .the method of securing the uprights is with spring loaded studs as seen in
> > > adjustable crutches and lever actuated cams(from aluminium sliding windows)
> > > to clamp the urights firm.
> > > The total length of each upright is about 4 ft and with 1 ft( 30 cm) at top
> > > and bottom inside the larger boxes it leaves 2 ft in the middle. Will there
> > > be too much flexion on the uprights in view of this being only a double
> > > upright system?
> > >  Any advice? Thanks  John Akers  email jakers@cyllene.uwa.edu.au
> >
> > John,
> >
> > My brother-in-law built Alice, and I can guarantee you that all aspects
> > of the design were carefully thought out.  Your question on the use of
> > 19mm on a side square aluminum tubing prompts the following response.
> >
> > First I would not use square tubing! It will be difficult to get the fit
> > in the channel that will limit movement.  The original Alice can be
> > assembled and disassembled without the need to recollimate most of the
> > time, and if collimation is off it is just a tweak.  Ron used 1 1/4 inch
> > (about 32 mm) round tubing which pulls into the channels tightly and
> > there is only one way the tubes can fit the channels.
> >
> > Secondly, the 19mm per side is way too small.  What I would suggest is
> > to find an Engineering handbook and look up the moment of inertia for a
> > round cross section and calculate the deflection for some load (say 5
> > lbs) and then, using the moment of inertia for a square cross section
> > calculate the size required to achieve the same stiffness.  I think the
> > answer will drive you to the round cross section.  If you want help with
> > this calculation let me know.
> >
> > If you follow the original design you will end up with a very sweet
> > scope.  Good luck!
> >
> > --
> > Bob
> >
> > rscholtz@iquest.net