Re: 12" cones....
You have missed the point completely
The precession of the top is the product of its rotational velocity, its moment of inertia and the torque created by gravity (the COG of the top is displaced from its support centre). Since we are talking about TT platters at constant velocity we need only consider the moment of inertia and the torque.
By attaching a string to the top you are cancelling the torque thus removing the precession.
In the TT system this does not occur because there is always a torque due to the VTF of the stylus
Accordingly, it is only the "stiffness" of the bearing which prevents precession. The stiffness of a hydrostatically lubricated bearing is a function of the film strength and film thickness of the lubricant and the bearing tolerances.
Nanook said:
You have missed the point completely
The precession of the top is the product of its rotational velocity, its moment of inertia and the torque created by gravity (the COG of the top is displaced from its support centre). Since we are talking about TT platters at constant velocity we need only consider the moment of inertia and the torque.
By attaching a string to the top you are cancelling the torque thus removing the precession.
In the TT system this does not occur because there is always a torque due to the VTF of the stylus
Accordingly, it is only the "stiffness" of the bearing which prevents precession. The stiffness of a hydrostatically lubricated bearing is a function of the film strength and film thickness of the lubricant and the bearing tolerances.
vinylkid58 said:
Why can't you use the Haas mill mentioned in post #11, acrylic isn't hard to machine.
Jeff
It's not that simple. I could have gotten a piece of Acrylic for much cheaper than the aluminum. The problem is heat. The vinyl will not machine well with normal machine bits plus it not my shop. My neighbor owns the shop and he frowned at machining plastic.
I know very little about UHMWPP but I would expect it to behave like other UHMW polyolefins and be light, slippery and not very rigid, so it will have a lower acoustic impedance than vinyl.
Of the materials you've mentioned so far Corian seems to have the most interesting properties. Corian is basically a mineral filled acrylic, it's between vinyl and aluminium in density and in stiffness (though its stiffness is much closer to vinyl than aluminium).
Of the materials you've mentioned so far Corian seems to have the most interesting properties. Corian is basically a mineral filled acrylic, it's between vinyl and aluminium in density and in stiffness (though its stiffness is much closer to vinyl than aluminium).
agree or disagree...
Mark, I wasn't offended at all because, I believe the point was/is a mutual understanding/education. As long as comments aren't: "you're ....." I consider them to be non-offensive in anyway. I did try to email you directly, but you don't accept emails via diyAudio, nor on your website. I try not to allow myself to get too centered on "bickering", as it doesn't seem to do anyting but annoy others.
Regardless, I still agree with the Audiomecca bearing concept, to reduce the lateral load on the bearing, or bushing wall.
And please read the comment regarding the inverted bearing vs the Teres bearing...
"Bearing
As we studied Scheu's inverted bearing design, it became readily apparent that the reason for this architecture was to reduce lateral thrust on the bearing surfaces. Conventional (upward opening) turntable bearings are less dynamically stable (they tend to teeter-totter like a top on its point) and create larger side loads on the bearing sleeves and so are more prone to a "wow" type of distortion by allowing (a microscopic) teetering and wobble of the platter. In addition the pull of the drive belt is well above the bearing causing additional side loading of the bearing.
Thomas Sheu's approach was to place the inverted bearing in the platter thereby placing the platter center of gravity at or below the bearing midpoint. This also made it possible to align the pull of the belt with the center of the bearing. This is clearly a superior approach that would result in better dynamic stability. However, the inverted bearing does not allow the use of an oil sump which provides consistent lubrication and a high degree of viscous damping.
The Teres bearing design is a traditional upward opening bearing. However, as in the Sheu design the majority of the bearing is placed inside of the platter. This provides the same dynamic stability as the Sheu bearing and also allows for the use of an oil sump along with it's inherent benefits"
so it seems that the Teres guys thought about it, but made a decision. At least they considered it.
I'll look at the mathematics and Vector analysis to agree or disagree with Mark.
stew
Mark, I wasn't offended at all because, I believe the point was/is a mutual understanding/education. As long as comments aren't: "you're ....." I consider them to be non-offensive in anyway. I did try to email you directly, but you don't accept emails via diyAudio, nor on your website. I try not to allow myself to get too centered on "bickering", as it doesn't seem to do anyting but annoy others.
Regardless, I still agree with the Audiomecca bearing concept, to reduce the lateral load on the bearing, or bushing wall.
And please read the comment regarding the inverted bearing vs the Teres bearing...
"Bearing
As we studied Scheu's inverted bearing design, it became readily apparent that the reason for this architecture was to reduce lateral thrust on the bearing surfaces. Conventional (upward opening) turntable bearings are less dynamically stable (they tend to teeter-totter like a top on its point) and create larger side loads on the bearing sleeves and so are more prone to a "wow" type of distortion by allowing (a microscopic) teetering and wobble of the platter. In addition the pull of the drive belt is well above the bearing causing additional side loading of the bearing.
Thomas Sheu's approach was to place the inverted bearing in the platter thereby placing the platter center of gravity at or below the bearing midpoint. This also made it possible to align the pull of the belt with the center of the bearing. This is clearly a superior approach that would result in better dynamic stability. However, the inverted bearing does not allow the use of an oil sump which provides consistent lubrication and a high degree of viscous damping.
The Teres bearing design is a traditional upward opening bearing. However, as in the Sheu design the majority of the bearing is placed inside of the platter. This provides the same dynamic stability as the Sheu bearing and also allows for the use of an oil sump along with it's inherent benefits"
so it seems that the Teres guys thought about it, but made a decision. At least they considered it.
I'll look at the mathematics and Vector analysis to agree or disagree with Mark.
stew
Platter stability
What Cris Brady's platter/bearing design is trying to achieve is placing the platter CofG closer to the bearing midpoint, i.e. geometrical center of the journal bearing. This is the only way to minimize adverse effect of the belt tension and platter rocking. It is completely irrelevant, where the ball is located (conventional or inverted bearing).
Teres design moves the bearing center closer to the platter CofG, but the ultimate goal (both of them are in the same point) is still not achived. I just want to note, that it is not feasible for single-material platter. If you want to keep reasonable platter thickness, you have to make the lower part of the platter much heavier, than the upper part (or use short bearing - no go). Put your ballast under waterline, just as shipbuilders do.
I'm currently working on wooden top and lead shot loaded Alu bottom platter, which has the bearing center, platter CofG and belt plane perfectly coinscided.
Cheers,
Michael
What Cris Brady's platter/bearing design is trying to achieve is placing the platter CofG closer to the bearing midpoint, i.e. geometrical center of the journal bearing. This is the only way to minimize adverse effect of the belt tension and platter rocking. It is completely irrelevant, where the ball is located (conventional or inverted bearing).
Teres design moves the bearing center closer to the platter CofG, but the ultimate goal (both of them are in the same point) is still not achived. I just want to note, that it is not feasible for single-material platter. If you want to keep reasonable platter thickness, you have to make the lower part of the platter much heavier, than the upper part (or use short bearing - no go). Put your ballast under waterline, just as shipbuilders do.
I'm currently working on wooden top and lead shot loaded Alu bottom platter, which has the bearing center, platter CofG and belt plane perfectly coinscided.
Cheers,
Michael
Attachments
Since you got the Teres bearing, you should work from your bearing up. Use the KISS principle. There is so much documentation on the Teres. The bearing is the heart of your TT. They have a recommended lube. The lube will work best with certain range loads and temps. Too heavy/light a platter will cause you problems. The aluminum will suck the heat out of the bearing. But, that should be within the range of the lube. Then again, worth checking out. Just in case there is a "magic" temp or weight. IIRC they use arcylic and Cocobolo. Bearing break-in is crucial, I'd find out what the Teres guys do. The lead shot should be loaded from the bottom of the platter, just like the Teres. Did I say you should make a Teres?
. Other than that, I don't know nuttin', don't have a Teres.
BTW, thanks for the beautiful job on the plates.
. Other than that, I don't know nuttin', don't have a Teres.BTW, thanks for the beautiful job on the plates.
woodturner-fran said:
Thats pretty much what I did do. I am a novice and going into this did a bunch of research. I felt real comfortable with aluminum because the Redpoint bearing is very similar to the Teres bearing and almost interchangeable with the Teres bearing. The reason I chose to model mine after Redpoint is because of the similarities between the Teres and Redpoint. As a matter of fact Peter Clark the Redpoint Turntable Designer was a participant in the original Teres Build. Another reason I chose to model mine after Redpoint is because I have no experience building a suspension so I decided on a High Mass design. I would bet that the Teres Platter has the shot loaded from the bottom is because they want a flat and solid surface for the vinyl to contact instead of having unsightly screw-in plugs face the top. I hope to have multiple arms and by using multiple well damped arm pods, I can easily achieve that. Once the table is built, I can also experiment with different platter designs with too much trouble because the rest of the table does not have to change.
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