On 13 Oct 2005 11:08:49 -0700, "Dave" wrote:

I recently picked up two nice older indicators on Ebay; one analog, one
digital. It seems that older indicators tend to go fairly cheaply
(especially true if they are not Starrett or Mitutoyo or another big
name). My question is this -- what common problems might be found with
such older units and what cautions should apply to cleaning them up?
Thanks!
I like older Mitutoyo 1" travel indicators. I haven't bought a new one
for a long time but if they're still made the same then the older ones
are good. Indicators branded "Westhoff" used to be made by Mitutoyo.
They may still be. The Mitutoyo test indicators should be avoided.
Things to look for when buying a used travel indicator:
Check the fit of the moving rod. There should be no discernable
side play.
Check to see if thickened oil is making it drag.
The sleeves the rod runs in, which are attached to the body of the
indicator, can be knocked out of alignment. This will prevent the rod
from moving without drag. They can be pushed back into alignment. If
this is done too many times they will get loose. So grab the indicator
body and apply gentle pressure to the sleeve and see if the rod starts
to drag.
Check for smooth travel of the rod. Look for grit in the gear teeth
on the rod and the gear that rides on the rod. These teeth should not
be visible without removing the back of the indicator. So there should
be no way for chips to get in there. But they do. Osmosis or
something. You know, less chips inside, more chips outside, so the
chip pressure is higher outside and they pass through the indicator
case in an attempt to equalize the chip pressure.
Inside is a thin, short, rod with a spring attached that is pressed
into the moving rod. They can become loose. This can be fixed with the
careful use of loctite.
Someone may have taken apart the indicator and not put it back
together with the backlash removed. The gear train is spring loaded
such that the gear that rides against the rod is always trying to push
the rod out. This is how the lash is removed. The indicator can be put
together without the proper loading of the gear train.
Finally, the hands may not be tight on their shafts. Check this by
first setting the indicator to zero and then tapping the tip of the
indicator sharply with your finger. Don't go overboard though. The
hand should return to zero. It's harder to see if the little hand is
loose but they almost never get loose. But the big hands do. So if the
big hand is a little loose it will lose or gain motion in the same
direction so that it will get farther and farther away from zero. If
it's really loose it will end up on either side of zero depending on
how hard you tap the indicator.
Well, lunch is over and I can't think of anything else.
ERS