16 Nov
2003
16 Nov
'03
2:20 p.m.
According to the Navy school where they taught us to fix these, the
discussion of the runout and flatness is correct, although I remember
that you had to check the flatness for an entire revolution. But it's
been at least 10 years since I had to replace a fixed platter on one...
The steel ball on the dial indicator was not coated, and (if I remember
correctly) you were supposed to position the ball at extreme edge of the
upper surface, right where the bevel is, and there is a picture in the
service manual showing it. There was a hole specifically placed in the
chassis, back by the card cage I think, that you placed the post
attached to the dial indicator into. The dial indicator had a little
switch to change from measuring runout and flatness.
It was a special dial indicator. I did a google search and I think it's
in tool set A31U11908-1, if you know anyone still in the Navy or with
Grumman... I think the Navy repair manual for the drive might be NA
16-45-2100-43 or AT-828CA-MMC-020.
TTFN
Andrew
On Sun, 2003-11-16 at 19:12, Jay West wrote:
Wizard wrote....
Runout is side to side oscillation (off center)
Think of the stick
on sanding disk not perfectly centered on the rubber base.
Aha! This makes
sense... that's why they would put the ball touching the
"vertical" edge of the platter.
Flatness is how perfect it is (90 deg to the
axle) with very little
or no wobble. Think of a spinning top slowing down and it get wobbly
by the second. Also checks for bow-ness.
I thought so, which leads to...
I agree having that steel ball touching media is
BAD day. :-)
The platter is turned by hand less than one revolution during the
test, it's
not at 3600 rpm when the ball is on it. But it sure LOOKS like they put the
ball right on the media surface. Specifically "Place the ball so that it
rests on the top outer circumferance of the fixed disk within 1/4 inch of
the outer edge". This would be outside the head loading zone... but still.
The manual doesn't mention it, but I wonder if the dial gauge from them is
special because it has a rubber tip or something. Still not good on the
media I wouldn't think. Odd.