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Old 10th January 2006, 11:42 AM   #1
diyAudio Member
Join Date: Dec 2005
Location: essex
Default quick question about platters and belts

If i make what im thinking of the belt will run around the diameter of the platter. Is there an optimum height compared to the bearing?
It would seem a good idea to me to have the belt at the same level as the ball.
Im making a bearing, the type with a tube around a rod, with the ball on top of the rod and the tube in the platter.
Hope this all makes sense, im not very good at describing these things as designing tt's is new to me.
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Old 10th January 2006, 01:18 PM   #2
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK

you seem to be describing an inverted bearing.

Generally accepted that the ball bearing point of contact should
be as high as possible, i.e. the C of G of the platter is below this
point and consequently "stabilises" the platter position.

Compared to a normal bearing where the C of G is far above
the thrust contact point and no "stabilisation" is possible.

I can see the arguement that the drive should be applied in the plane
of the inverted contact point, however if this compromises the height
of the contact point to do it, then I think height should take precedence.

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Old 11th January 2006, 12:47 PM   #3
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Location: essex
thanx, once ive settled on a design ill see what everyone thinks before i build a prototype.
I also now know how to desribe my bearing design too
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Old 11th January 2006, 03:07 PM   #4
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Location: essex
theres an idea i cant get out of my head, but is it a good one?
I was going to use this inverted bearing, with a heavy platter with the CoG below the ball. Probably laminated wood platter
I was then going add 3 spikes about 2 inch in from the edge, say 1/4 inch high.
On top of this i was thinking of adding an acrylic or similar platter say 1/5 - 1 inch thick with the center pin on it.
I wanted to do this to isolate the top platter, and keep contact with the record far away from any possible vibrations at the center caused by the bearing.
Hopefully these vibrations wont be there and im trying to fix a problem that doesnt exist, but it all helps.

Also, can someone explain the eccentric center pin workings, to center eccentric records?
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Old 16th January 2006, 01:08 AM   #5
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Location: Thailand
If it's the one they (used) to use on the Rokson Xerxes (spelling?) you essentially have a thin "needle" say, 1/16" dia where you'd normally expect to find the centre pin. For every day use, a broader sleeve fits over the top of this and looks just the same as any other conventional locator. When you encounter an eccentric record, remove the sleeve & manually position until you're satisfied with the results. If you have anything as adherant as a felt mat or better on top of your platter, the disk won't move. If you want a disk-acrylic contact, thread the needle (sorry!) and make a clamp.

Cheers - Fez
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