Runout vs. Flatness and Dial test indicators

From: Don Maslin <donm_at_cts.com>
Date: Sun Nov 16 22:24:34 2003

On Sun, 16 Nov 2003, 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.

If it did, the readings would likely be erratic. More likely,
that 'lever' that you referred in a prior message is to retract
the ball from the surface while the disk is rotated by hand.

                                                - don
Received on Sun Nov 16 2003 - 22:24:34 GMT