[ATM] How dark is dark?

[Don Clement]

Someone wrote  (in jest) offlist "So you should get a gigantic tap (as in
tap and die) and thread the inside
of the telescope tube.

;^) "





Actually I single point thread using the lathe. Right hand internal
threading is done using the reverse helix method where headstock is rotated
in reverse and travel is to the tailstock using a left hand insert holder
with internal left-hand inserts. This method allows to manually thead right
up to a shoulder at high speed.  The proper anvil is chosen for the
particular helix angle (a function of pitch and diameter) of the thread. The
anvil tilts the threading insert  so there is ample side clearance for
chips.



  I also make my own taps. Shown is a 5/16"-11tpi double-helix tap
http://i72.photobucket.com/albums/i163/miltons_stuff/doubleStartTap.jpg
that I made and use for tapping the leadscrew nuts for my focuser.



Where impractical to single point thread in lathe, I have found that lining
the sides with black felt works well. (100% cotton felt from Belgium is
best ). Felt has thousands of tiny hairs, which work similar to stacking
razors.



Don Clement

Running Springs, California