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Old 14th January 2012, 04:51 AM   #11
Nanook is offline Nanook  Canada
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Default torque...

Mark, I was thinking about the inherent torque of a motor without taking into consideration based on any possible gear ratio.
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Old 14th March 2012, 12:00 AM   #12
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Has anyone had success with a similar implementation on a rim drive? The outside of my platter is 13" and weighs about 25lbs.
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Old 25th April 2012, 08:21 PM   #13
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I got a quote from Choir Audio for a 2" platter polished and their bearing for $1300.

If you can use acrylic, 8audio.com has a platter for just over $200 with $80 shipping.
I bought an attenuator from them and the quality was good. Haven't purchased a platter, but strongely considering it.

BTW- the Choir Audio DIY parts are no more. They only make custom platters or you can buy their table.
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Old 25th April 2012, 09:15 PM   #14
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I've looked at the 8audio platter and bearing. I didn't think the bearing housing and spindle were anywhere near long enough to offer decent sideways support.
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Old 26th April 2012, 03:16 PM   #15
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Quote:
I didn't think the bearing housing and spindle were anywhere near long enough to offer decent sideways support
I'm trying to understand what you mean by "sideways support", and I can only assume you mean the way the belt pulls around the side of the platter toward the motor. If the bearing is a slip fit, how could it be a problem?

I was going to either have two motors (not likely) or use something like a "fly wheel" so the belt touches both side equally when rotating the platter.
See attachment. Not drawn to scale.

In either case, a new bearing is easier to turn on a lathe than a platter.
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File Type: jpg lpbearing2.jpg (260.4 KB, 926 views)
File Type: jpg platterconfig.jpg (29.5 KB, 886 views)
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Old 10th May 2012, 05:35 PM   #16
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The platter arrived in the mail today. Well packed. Looks very nice.

I am told the platter is concentric to 1/1000th. The bearing is bigger and heavier than I thought it would be.

I picked up their 700g record weight. Also very nice.

Now for the hard part...
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File Type: jpg acrylic_platter_1.JPG (404.0 KB, 835 views)
File Type: jpg acrylic_platter2.JPG (93.9 KB, 798 views)
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Old 11th May 2012, 02:04 PM   #17
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most of the plater is above the centre point of the bearing, it's less than ideal in terms of side loading.
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Old 11th May 2012, 02:52 PM   #18
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Quote:
most of the plater is above the centre point of the bearing
I noticed that, but it's fine for what it is. The bearing plate goes in about 1/8 the depth of the platter. I would have liked to seen it go 1/2 way, like the Choir platter. That platter is $1000 more. For that money, I would just buy a VPI Traveler. This is fine for a DIY build.

Once spinning, it just keeps going. It's not warps and I'm happy about that fact.
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Old 11th May 2012, 03:24 PM   #19
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You know, this had me thinking (dangerous, I know!) about the issue of side loading etc. A top heavy platter above the center point could create more side pressure on the bearing but this may be less of an issue when the turntable is running. Think of a spinning top or a gyroscope, when they spin they stay in a more balanced vertical stance. May be somewhat the same with a turntable platter in motion.

Now I know that gyros and tops spin at much higher speed than a turntable platter, but perhaps the forces at play are still an influence with slower turning tt platter speeds but relatively high mass of the platter.

Normally we would want reduced side pressures during play to reduce vibration and rumble. If this is the case, then what would be important is that the spindle and platter assembly are perfectly concentric and balanced.

Hmmm, just a thought.
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Old 12th May 2012, 01:08 AM   #20
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Any spinning object subjected to a force which attempts to tip the axis of spin (eg a torque applied orthogonally to the axis of spin) reacts to that force by precessing. Precession casues the contact point of the spindle in the bearing to revolve constantly.

The frequency and the force of the precession are easily calculable if you know the velocity and inertia of the spinning object and the deflection torque. In the case of TT platters it's a very slow but very powerful force.
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