One More Fix

[Tom Droege <tdroege@veriomail.com>]

Sigh!  It seems there is always one more thing to make better.  This 
morning I woke up at 4 AM thinking about how to fix the focus drive on 
MICHAEL.  One camera focuses OK, the other has a sticky trombone drive and 
this tilts the camera.  Any musical experts out there on trombones?  Note 
that you "drive" a real trombone from one side and it works just 
fine.  When I think about it, I bet this is a tricky thing to make.  Does 
anyone know if a slide from one trombone will fit on another?  I bet it is 
not so easy to switch.  I bet they are custom fitted at the 
factory.  Mechanical slides like milling machine tables are designed so 
that the ways do not have to be exactly parallel.  One normally avoids 4 
bearing designs - as mine is.   A real trombone has continuous bearings on 
each side.  They really have to be exactly parallel to the tolerance of the 
slide fit.

The problem is that the Mark IV design is pushed from one side.  The 
trombone wants to tilt.  This causes the bearing rods to move closer 
together, which binds the bearings.  The more the push the more the tilt 
and the bearings stick tighter causing a really unstable situation.  I 
glued the slide rods in the support bars to attempt to reduce the 
tilt.  This worked in one case on MICHAEL and greatly reduced the tilt.  On 
the other, the now tighter situation bound even more.  I note that a real 
trombone has a brace between the tubes on the slide about half way down 
where you hold on to it.  This makes the slide much more rigid, and 
prevents the problem that I have.  There is no place (now) in my design to 
add such a stiffener.   Well, nothing is impossible, but it would be really 
ugly since the lens occupies the space between the slides.   What I need is 
a plumber.  When they were putting in my addition, the plumbing for the 
waste pipe appeared to be impossible.  The plumbers attitude was "We just 
do what it takes".  So the soil pipe comes out of one foundation and into 
the other.  Ugly, but it works.

Sigh!  I have a possible solution which allows pushing from the middle 
which I will try today.

Tom Droege