Runout vs. Flatness and Dial test indicators

From: Andrew Prince <freddyboomboom_at_comcast.net>
Date: Sun Nov 16 22:20:00 2003

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.
>
Received on Sun Nov 16 2003 - 22:20:00 GMT