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Platter Levelling Issue

I have just purchased a new "bullseye style" bubble level that has graduated markings on it to allow you to determine the degree of misaligned conditions - each marking is supposed to represent 5/1000's of a degree

I initially verified it's accuracy by levelling a flat surface and then rotated the level in the horizontal plane in place - the position of the bubble did not move as I rotated it through 360 degrees.

I then placed the level on the plinth by the base of the arm and levelled the turntable - I believe the mounting method of my arm should ensure the arm is now perpendicular.

I then place the level on my turntable platter and took a readings as I rotated the platter through 360 degrees

Turns out the platter is not quite parallel to the plinth
- I don't think the bearing is damaged, since the degree of misalignment was consistent and always in the same direction as I rotated the platter - so the platter is not quite aligned with the plinth

The margin of error I observed is 10/1000's of a degree according to the gradations on the level

So, until I can rectify this - my questions are...

1. should I ensure the platter is level at the expense of a perpendicular arm

2. should I ensure the arm is perpendicular at the expense of a horizontal platter alignment?

3. Am I being 10-1000's of a degree anal :-)

The arm is an Audiomods Series 3 that has Rega style bearings and from what I have read on the web it is more important for arms with a bearing system like the Rega to be perpendicular

I have read other posts on Agon of a similar nature, but there was no mention as to the degree of misalignment

Any input would be very much appreciated

Many Thanks
williewonka

Showing 2 responses by minkwelder

minkwelder
255 posts
 
I should correct something I said earlier. I said "you'll never get it perfect". That's not entirely true. You could very well get it perfect, but there is no way you'll ever know for certain!

The graduations on your level are most likely intended to indicate how out of level the surface is in some fraction of a degree, but don't concern yourself with that. Just use the markings as a reference to verify that the bubble doesn't move as you rotate the level through 360 degrees, and you've done as well as you can realistically do.
minkwelder
255 posts
 
"...each marking is supposed to represent 5/1000's of a degree."

As a surveyor, I was constantly dealing with error; something that is always there in even the most precision instruments available. So, the first thing to do is accept that you'll never get it perfect.

On surveying instruments, bubbles are generally used for rough leveling, and other mechanisms are used to increase the precision. Without knowing the particulars of the level you used, I have my doubts that it can be read accurately at that level of precision. Rotating your bubble level is the sort of method that is used by surveyors in order to eliminate as much error as possible, so you have done what you can within the limits of the tool you're using.

Now, the question remains; if you have a measurement you can trust, is 10/1000's of a degree something to worry about? In the span of a foot, it amounts to a difference of about 2/1000's of an inch; a little less than the thickness of a standard sheet of printer paper.

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