Shugart 800-8 media centering problem

[Jay Jaeger]

On 8/15/2015 1:35 PM, tony duell wrote:

> 
>> Not so on these drives.  On the Shugart SA-800 series, the spindle
>> (driven by a belt from a motor) has a MALE cone on the end, and the
>> clamp, from above goes around it (female if you like).
> 
> I have just pulled the case on one of my HP9885s, which uses an SA801 
> chassis and HP electronics. The spindle clamping mechanism is as you
> describe. I took the cover plate off the clamp arm and looked at the 
> (female) cone, etc.
> 
> The cone is in 2 parts, with a bearing between them, the outer housing 
> doesn't rotate in normal operation. There is also a spring ring round the 
> outside of the nylon fingers. BUT I don't see how any of this has anything
> to do with centering. If the disk is pushed down onto the male spindle end 
> (and yes, the disk guides do move with clamp arm) it will centre. So all that
> really affects things is the metal spinde.
> 
> I suppose gross errors in how the clamp comes down could do it, but 
> unless the clamp arm is hanging on one pivot only, or something, I don't 
> think that's it.

I tend to agree.  The nylon piece does pivot just a little, and, after
all, the clamp does come down on the inside part of the drive just a bit
before the outer/front side of the drive.

> 
> It virtually has to be a problem with the male cone end. I think you
> need to measure that carefully and compare the measurements with
> a good drive, look for burrs and wear. Remember that 10 thou is not
> much. 

I'd have to buy something to measure with (not a big problem).

No burrs.  Already checked for that, and polished the upper conical part
(above the vertical part where diameter becomes critical).  That was
part of my first guess that maybe the media was hanging up on the cone
somewhere on the way down.

Wear is certainly possible, but as I pointed out in an earlier message,
the media isn't supposed to slip during use, so there ought not to be
all that much wear on the spindle cone.

> 
> What if, due to some problem with the spindle cone, it clamps on one side
> before the other? That could cause the disk to skew round and loose centering 
> I think. 

Certainly one of my thoughts along the way.  But, the spindle cone does
not rock or anything like that.  And, I switched the clamping part out
with another drive - neither was affected by the swap.

> 
> -tony
>