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Old 27th February 2019, 02:21 PM   #2781
nocdplz is offline nocdplz
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The belt/belts are also positioned as far below the pivot as practically possible. In this way a small tilt of the platter will result in a larger change in belt tension.

Very interesting Niffy, and really counter intuitive: I thought that a lever arm (distance of the pivot point from belt) multiplies the effects of a non-homogeneous tension (frictions from two idler), but your experience says the opposite This also explains why the solution with three belts can work better.

carlo
addendum
The runout (with the noise) is a big problem, not having a big size lathe. After trying to get a sandstone platter waterjet cut and drilled (not straight, now good as lamp holder) I came to a machined sub platter with 3 register screws: with a dial gauge the runout can be registered under the tenth (tolerance of the sleeve x radius)

Vpi style bearing: I tried with two opposing Teflon V-angles, one up and one down, with the belt forcing the spindle against each other. Result: random friction = irregular rotation. Maybe the surface of Teflon was not smooth enough, or maybe too much: who knows.
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Old 27th February 2019, 02:29 PM   #2782
walterwalter is offline walterwalter  Ukraine
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The sleeve seems to be the part of the bearings that causes the biggest problems, has the largest negative impact on sound quality and is the most difficult and expensive to manufacture.

I got the idea for eliminating the sleeve from the days when I owned a pink triangle anniversary deck. This used an inverted bearing and a Teflon washer in very much the same way as Hiten suggested. I found that removing the washer gave a large improvement in sound quality even though the platter wobbled all over the place. The negative effects of this simple sleeve were still greater than a couple of millimetres of runout. Don't get me wrong, the anniversary is still one of the greatest decks ever made.

Niffy, what is the influence of bearing sleeve on sound, and how would you explain the process?
Walter
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Old 27th February 2019, 05:06 PM   #2783
hottattoo is offline hottattoo  United States
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nocdplz,

I feel your frustration in making your own platter / bearing as it is totally unforgiving for lack of precision tolerances being maintained. Teflon is not a good material ( soft and "tears" ) for the sleeve part of the bearing. Vespel or Torlon (very expensive) are the best sleeve materials, bronze also works well and is traditionally used for this purpose. . The concept of "just spinning a record" seems very simple, until you try to do it yourself in a quiet accurate manner. You can check into possibly obtaining a Rega or similar bearing. There are lots of Rega mods for platters, bearings, tonearms etc. that work very well and are cost effective on the net.

There are also turntable platters / bearings available on ebay. Good luck.
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Old 27th February 2019, 07:00 PM   #2784
niffy is offline niffy  England
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Hi Walter,

A normal turntable bearing, be it inverted or non-inverted, consists of two parts. The first one is the thrust plate . This tends to consist of a ball or round ended rod pressing against a pad that can be flat, concave or even convex, like a second ball. The thrust plate takes the entire weight off the platter and the load is thus vertical. I'm ignoring magnetic and air bearings as these are not "normal" turntable bearings. For any material combination of ball and pad there will be a maximum pressure that can be applied safely. Any turntable using the same materials and platter mass and having the same contact pressure will have the same contact area and pressure distribution across that contact area. For example my turntable with a platter mass just shy of 4kg and hardened steel ball and concave thrust pad has a contact point 0.25mm across. Any turntable with the same mass, using the same materials and keeping the same maximum contact pressure will have the same 0.25mm contact point regardless of the shape of the thrust plate used. The pressure gradient across the contact point is always the same with an elliptical profile. As the platter rotates the contact point of the ball slides over the thrust pad creating a frictional torque. The point of maximum torque is always 82% of the radius of the contact point from the centre and the average at 60%. (I accidentally quoted the average as 80% in a previous post). My bearing has its 4kg mass acting at a point only 0.075mm from the centre of rotation. The coefficient of friction between thrust pad and ball is 0.19.

The second part of the bearing is the sleeve. Most sleeves are made of a combination of steel and bronze and are lubricated with oil. The sleeve doesn't take any of the load required to support the mass of the platter. It has to be produced with a very small gap between the shaft and sleeve in order to run true. This gap is filled with a laminar film of oil. This results in a large drag. Bearing shafts tend to be at least 8mm in diameter and are often as much as 20mm for high mass platters. The friction due to this drag is acting 4-10mm from the centre of rotation, 50-130 times further than for the contact point.

In a normal non-inverted bearing you can expect 93% of the friction to be due to the sleeve. Once you add the side force of the belt this is likely to be 95%. That means only 5% of the total energy dissipated is dissipated by the thrust pad. Even if the sleeve dissipates a smaller proportion of its energy as noise it can still easily produce a lot more noise than the thrust pad simply because it is dissipating so much more in total. The sliding velocity in the sleeve is going to be 50-130 times greater than in the contact point average. Of course you still have to have the thrust pad and its noise.

Similarly variations in torque due to inevitable limitations in manufacturing accuracy are going to be greater in the sleeve than the thrust plate. A 10% inaccuracy in the thrust pad is smaller than a 1% inaccuracy in the sleeve.

It's a difficult thing to pin down what the actual effects on sound quality are of the different components within the bearing. If you remove one component in order to listen to the other the bearing tends to stop working all together. As I previously mentioned the one exception to this was my pink triangle anniversary. Removing the Teflon sleeve resulted in a sound that can best be described as more open. This is despite the runout going to pot which would have had a detrimental effect on VTA, azimuth and wow. The gains were greater than the losses. Of course you couldn't sell a deck with this level of runout (2mm) even if it sounded as good as the pink. (actually you probably can, have you seen the magnetically levitated deck. It must have at least 5mm of runout. But that is sold as a gimmick)

Niffy
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Old 27th February 2019, 08:13 PM   #2785
walterwalter is offline walterwalter  Ukraine
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Niffy, thank you very much. I've never thought about platter bearing from that angle of view. A lot of material to think about...
Walter
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Old 28th February 2019, 07:45 AM   #2786
nocdplz is offline nocdplz
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Hi Hottattoo, my frustrations depend only from my fundamentalist concept of DIY: from scrap, on my own (tools, skill, ideas). That's the challenge for me, not to assemble Frankenstein TTs, or make me do parts by others.
Add to this that I do not like to fool myself, and that the experience made me quite demanding, and you will understand why to abandon the idea of ​​a diy turntable: simply because with a 9x20 Chinese lathe it is almost impossible (vibrations) to get the tolerances - finish necessary for a truly silent bearing.
There are no good or bad materials, imho, only the right materials to be used for the task: for bearings as for platters, plynths and so on. And for different solutions conceived for very different TT concepts.

Hi Walter: the influence of the bearing on the sound has been reported in detail by Niffy's experience+ knowledge. (a lot to learn for me too)
I always thought there were too many variables to be able to understand something, but instead I could say several things about the noise produced by different types of couplings, because I lost some time hearing my different trials with a stethoscope.
Since I like rigid TTs and a rigid disk to platter coupling, I know that the noises of the bearing are the first to reach the cartridge, and it is certainly not an heavy mass that can cut them: you can hear the clang of a train coming, through miles of rails and tons of iron.
carlo

Last edited by nocdplz; 28th February 2019 at 07:50 AM.
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Old 28th February 2019, 08:28 AM   #2787
walterwalter is offline walterwalter  Ukraine
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Niffy, your research, as I've said before, may challenge the whole R@D institution. Understanding the problems in order to eliminate or minimize their effect, IMO is a right way to go. It is not a dominating approach in the hi-end industry, and so, there is a room for DIY-ers activity.
As to my turntables, I'm satisfied with traditional bearings, because their noise and vibrations are of negligibly low level. That's why I've never thought about the elimination of bushing before. Possibly, it is worth trying in my case too.
Carlo, if we could eliminate the motor vibrations and flatter... Some people are back to spring motors of 1920-x years of the last century, and I even thought of trying them myself.
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Old 28th February 2019, 11:12 AM   #2788
niffy is offline niffy  England
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Hi all,

A couple of additional points to my last post.
The use of a sleeve type bearing with its thin film of oil will introduce some degree of damping, probably quite a lot. Whether this is beneficial or not is going to be open to debate. In many instances I have found that the addition of damping to be detrimental, the suspension of the deck for instance. The removal of damping may account for some improvements in sound quality.
With the bearing in my deck the only contact between the platter and the sub-chassis is a single very small point. This may offer better mechanical grounding.
I have not performed any experiments that would allow me to confirm whether these hypotheses are plausible or not.
One thing is certain. It would be impossible to build a traditional style of bearing with the equipment that I own. I'm with Carlo when it comes to wanting to build everything myself. Not being able to make a traditional bearing forced me to design an alternative. In doing so I could address what I thought was the main drawback of traditional bearings. I think my sleeveless design is in many ways superior to what is used in commercial decks.

Niffy
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Old 1st March 2019, 04:16 AM   #2789
niffy is offline niffy  England
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Hi all,

The last paragraph in the previous post isn't quite right. It make it sound like I designed the sleeveless bearing because I couldn't build a sleeved one. I decided on the sleeveless approach because of the result of my experiment on my pink triangle deck and all the subsequent research. That the design I came up with is much more DIY friendly was a bonus.

Niffy
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Old 3rd March 2019, 08:51 AM   #2790
Coolerooney is offline Coolerooney
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Hi all,

Ok got my first Igus stuff in, now going for a Proxxon cut off saw

Dumped the floating platter for now, to much risk in flow overs when manipulating records, rings and the like

One of my tech sparring partners, mr Grimm, has a lot of words about eccentricity- with reason.
So looked at Nakamichiís TT, the tx 1000 centers on 2 axes,
Some nice shots under the hood:
YouTube


the dragon ct, uses 1 pusher to center the platter

YouTube

My question: what system is better and what is enough?- one axis should be enough-even though the measurement and 1axis alignment is a 45 degrees, when object is rotational, it should not matter, right?

Best
Coolerooney
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