Runout vs. Flatness and Dial test indicators

From: Don Maslin <donm_at_cts.com>
Date: Sun Nov 16 23:11:07 2003

On Sun, 16 Nov 2003, Jay West wrote:

> Andrew wrote...
> >(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.
> Yup, they say to make sure it is in the outer 1/4 inch of the media surface.
> However, they also specify to make sure it is not on the "extreme edge" or
> what I mean is, it must be in from the chamfered area. The picture doesn't
> quite do it justice :) Sure, there's never going to be any data there, but I
> would worry about microscopic particles coming off the platter where the
> ball rests (the media is coated to the very edge, no uncoated area visible)
> and flying particles of oxide are definitely not a good thing. But, it
> appears that is ok for this operation, and the way they specify to do it.

Do the illustrations indicate whether the dial indicator is in the
same general position (other than what part of the disk the ball
is contacting) for both runout and flatness? If so, my
supposition of lifting the ball from the surface is likely wrong.
I would then surmise that it actually converted the motion of the
ball from normal dial indicator to what we used to call a
'wiggler', IIRC, where lateral movements were shown as
displacements on the dial.

                                                - don

> > 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
> Just to the left of the heads actually, mirror image from the card cage.
>
> > The dial indicator had a little
> > switch to change from measuring runout and flatness.
> Yeah, now see, that's the part I can't figure out. Exactly what does that
> switch accomplish? I know one position is for measuring runout and one for
> flatness, but what does it actually cause to happen? The lever tony refers
> to is the joint in the guage, what I was referring to is this "switch" on
> the guage. Could it be that the older dial indicator wasn't auto reversing
> while newer ones are, hence, the switch?
>
> More specifically, I'm sure I'll never find the original HP dial indicator
> and holder bracket. So, I'm hoping to use "any old" dial test indicator (I
> know these terms aren't interchangeable). Harbor freight has a cheap one.
> The trick is the mounting bracket. As long as the dial indicator from harbor
> freight could be attached to the drive in a stationary way, I would think it
> would work for either test and that the HP dial indicator wasn't a "special"
> one.
>
> So Andrew, any idea why the dial test indicator on harbor freights website
> wouldn't work or easily be made to work?
>
> > It was a special dial indicator. I did a google search and I think it's
> Thanks much!!
>
> Jay
>
>
Received on Sun Nov 16 2003 - 23:11:07 GMT