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...if I roll my finger over it, should I feel it roll or should it feel 'stuck'?'Cause I'm experiencing some bearing noise, and someone suggested I check it; I just have, and it seems to be stuck—it doesn't roll, at least not freely.
Thanks!
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Many TTs have been designed such that the veritical support of the axial (rotation) bearing is provided by simply placing a hardened ball of some kind in the bottom of the well in which in the shaft sits. My old R-O-K K-33-H had a steel ball you just droped down the hole, put in some oil, and then inserted the TT shaft/axle. There are some intrinsic problems with this.First, the TT shaft has a rotation axis defined by its bearings. Generally this is well defined, because you don't want the TT to wander or wobble as it rotates. Unless the well in which tht ball sits is made to very high tolerance or has some very clever self-centering mechanism, it is likely that the ball's center will not lie exactly along the shaft's rotation axis. This means that the high point of the ball will not rest on the bottom of the shaft where the axis passes through it, but slightly off center. This means that the point of contact will not stay fixed on the end of the shaft, but will slide around in a small circle. I would assume that even if the ball could roll, forces would be such that the ball would stay fixed and the bottom of the shaft would slip on the ball as the contact point describes a small circle, but the ball could roll if it weren't fixed in place. How bad this is depends on the smoothness of that sliding contact, but I would think the ideal way thing would be to avoid it and have the shaft rotation axis pass exactly through the ball center.
One way to achieve what I say above is to attach the ball (or portion there-of to the bottom of the shaft and carefully machine the shaft or make things so that the ball is centered very accurately on the shaft. Then the the shat is supported by a flat plate at the bottom of the shaft well, and that part is much simpler. I have come up with some other designs for thrust bearings should I ever get ther urge to build a TT, but I think I would stay away from a simple ball dropped down a well for the reasons above. How bad this actually is in practice is another matter. I have some magnetic thrust bearing designs as well, but I haven't fully explored the eddy current questions.
When it comes to the overall machining on the Rek O Kut, it is far more precise than any other mass produced turntable I have measured. The run out on the main bearing was less than 0.0007 inches. The run out on the platter which is 11 inches was under 0.0020 after 35 years of use. Try measuring any of the other common turntables on the market and see if they are even close.Add to that, the main bearing well is cast iron which is vastly superior to steel, brass, or bronze in terms of resonance control.
The ball bearing is captured by a tapered area machined in the center of the bearing well.
It is at least as accurate as a captured ball system and probably easier to maintain over the decades. Simply replace the ball every few years and replace the oil as necessary.
By simply polishing the thrust plate, and utilizing a silicone nitride ball I am several orders quieter than my old Linn or Thorens turn tables. I can clearly hear the musicians flip the pages, shuffle their feet, and place their bows on the stand. I have heard this same level of precision on a 40k dollar Basis set up. This is seriously fun low level detail.
Measure any turntable you care to evaluate and tell me what you read.
The ball centered in the bearing well is under very high load. It will not rumble. If you doubt this, simply measure the thing with a scope. Many of the Rondine Rek O Kuts listed rumble as -67db (idler models) to -78db (belt driven models). This equals or supasses more than a handful of well respected turntables on the marketplace today.
They achieved this rumble level without polishing the main bearing or thrust plate. Just with fine machining and nothing more. This is quite an accomplishment. The machining on the Rek O Kut is thoroughly first class. Polish the damn thing and you will think you are listening to a world class top level vinyl set up at a CES show.
I built that ROK TT from a kit and was very impressed by its design. I still remember more than 45 years later the day I poured some oil down into the well, put in the ball, and lowered in the shaft. The fit was obviously very well machined. I was never able to detect any rumble from the TT, but had a lot of acoustic feedback on loud music mainly because I was ingnorant in those days on how to support a TT and my AR 3 speakers could put out a lot of bass. I followed it with the "new" AR TT, which I thought was flimsy in comparsion, but it cured the feedback problem.
Had I known Thorens es (Thorii?) were so fiddly, I'd have gotten something else.
smoothly, when you push it with your finger. Not loosely, but easily.
"The Blues ain't about makin' yourself feel better; it's about makin' other people feel worse!" -- Bleedin' Gums Murphy
I'm not familiar with the ball at the end of the TD-125 spindle, but I'm curious as to why it needs to roll. The reason I ask this is because the ball in my turntable spindle does not roll. It is there just to provide a rounded contact surface with the thrust plate.I used to own a TD-126 and it didn't have a ball, I don't believe. The spindle shaft was rounded on the bottom and I guess it simply road against the thrust plate, but I never looked into the bearing well to see if there was a ball down there.
Anyway, I'm just curious. I'm not suggesting the ball shouldn't roll; I'm just asking why it should roll if it is simply the contact ball for the thrust plate.
OK, I hadn't thought of all that. My thorens bearing was movable before i replaced the ball, since I could rotate a wear spot out of the action. But it wasn't so free that it would roll on its own. So even if it's stuck I suppose it would ride on the thrustplate and turn just fine.Speaking of thrustplates, mine (I think) didn't have one since it was a TD-160 with a 150/125 bearing. I got one from Joel B. -- wow!
"The Blues ain't about makin' yourself feel better; it's about makin' other people feel worse!" -- Bleedin' Gums Murphy
Re: "I'm not suggesting it should roll". I am. As you note, the object of using a ball end is to provide a small, centred contact area. It seems to me that if the ball has enough clearance to roll it will move in response to precession forces on the platter and this will increase rumble.
Your post said;Re: "I'm not suggesting it should roll". I am.
This seems to say that "I am... saying it should roll".
My error, I meant to quote John "I'm not suggesting it shouldn't roll" but I misquoted. Sorry about the confusion.Just to be clear, I am suggesting that the ball should be fixed. It should not roll. As I see it, any relative motion of the ball and the spindle will increase rumble.
Yes I understood that that was the case and in my opinion this is preferable to the loose ball approach used by Thorens. The bearing I designed for my idler wheel replacement also has a fixed ball. I haven't been able to try it because the machinist hasn't done it yet.
I suppose it would be fine for it to roll, but in actual application it probably wouldn't because the freer contact point would be at the thrust plate which is a chromed surface. That is the case with the Linn LP12 and the TD150, both of which use a captive ball system. The TD16x series turntables use a polished point, like you described, because there was no need for the ball, assuming an alternate method could be made as accurately. Thorens evidentially felt that they could make such a point with a radius accuracy to match the ball without compromise. Besides, it probably saved some time and money. That's what I believe, anyway.
I have some old Linn literature which shows a cross section of the LP12 bearing and spindle, and the spindle tapers to a polished point. I don't know about the Thorens.
Look at my post below. I caught the mistake three minutes before you did, so I don't look quite so dumb! ;)
Well...My turntable uses an inverted bearing with a zirconium ball sitting captive on a shaft the is inserted into the bearing bushing of the platter that contains a synthetic ruby pressure plate. The ball does not roll or rotate. It simply provides a hard rounded surface to contact the synthetic ruby pressure plate at the point of rotation.
I said that the Linn has a captive ball, but I need to double check that.
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