RE: arsclist RE: 78 Rpm Record Spindle Holes

["Audio101" <audio101@xxxxxxxxxxxxxx>]

Thank you for your insight! I just spoke with my machinist and I think
we have a solution!
 After examining how much of the spindle protrudes through the platter
and mat, I think we can machine PART of the spindle flat and undersized.
This would be lower then the bottom of the record surface, but protrude
enough to slip a sleeve over for normal record use! I think this might
be the best answer. This would work best with stock record mats, or mats
that are slightly thicker. But the thin felt type mats won't work for
this.


Dave

-----Original Message-----
> I am wondering how far off the center hole can be on a
> record?

Good question... 

I thought about the merits of an undersized spindle, but I decided that
a 
spindle with a removable top portion, that is, the part that protrudes
above
the turntable mat, would be the better idea.  The plane of the turntable
mat
is usually what the arm alignments are measured against, not counting
the 
thickness variations of the records being played.  This is one reason
why 
is not a good idea to build up the mat thickness when you encounter an
off
center disc (which most are to one degree or another!).
A maximum thickness LP pressing (from a major producer, say RCA Victor)
of 
the 60's would be the standard used for arm adjustment, and the thin LPs
of
the later years productions would fall a small fraction lower, which I
doubt
would affect play to any audible degree.

As far as centering is concerned, you will adjust it by moving the
record
to either side of the high point after placing it roughly over the 
approximate center location.  (Anyone who can't hit approximately center

without a center pin in place, really needs to examine what they are 
drinking or smoking!)

I do this a little more precisely with a groove microscope that is on my

transfer turntable, but often, eye-balling it seems to get it into 
"close-enough" territory for most people.  A record weight holds
everything
in place.

Look here to see it:-
http://www.audio-restoration.com/MVC-383F.JPG
Technics SP-15 turntable showing custom low resonance base, SME 3012-R
arm 
and Spencer/A-O groove microscope.  The silver thing at the 11 oclock 
position, to the right of the microscope pivot, is a record weight.

> What is every bodies experiences? Can they be more the 1/16" off
> center, if so, by how much?
If you adopt the above, the maximum degree of disc eccentricity becomes
a 
non-issue, although allowing for a 1/16" eccentric with a removable
sleeve 
out to the standard spindle size would cover most bases  For the very 
few that don't make it, a built up mat would suffice, or bore the center

hole of the offending disc with a tapered reamer as a last resort.



... Graham Newton

-- 
Audio Restoration by Graham Newton, http://www.audio-restoration.com
World class professional services applied to phonograph and tape
recordings for consumers and re-releases, featuring CEDAR processes.
-
For subscription instructions, see the ARSC home page
http://www.arsc-audio.org/arsclist.html
Copyright of individual posting is owned by the author of the posting
and
permission to re-transmit or publish a post must be secured
from the author of the post.

-
For subscription instructions, see the ARSC home page
http://www.arsc-audio.org/arsclist.html
Copyright of individual posting is owned by the author of the posting and
permission to re-transmit or publish a post must be secured
from the author of the post.