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In Reply to: Is the little captive ball at the end of a Thorens TD125 MkI spindle supposed to roll? As in... posted by Damián on April 23, 2007 at 17:18:03:
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
Follow Ups:
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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