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Old 23rd July 2013, 01:43 PM   #1
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Default Modern bearing engineering, a sad story

Some time ago i became the proud owner of a used Acoustic Signature bearing/platter assembly.

Proud does not necessarily imply happy as the bearing was damaged beyond belief.

Fortunately the seller turned out to be extremely patient and understanding and kind and at the end the monetary loss was quite moderate.

As can be seen from the pics, the bearing probably ran dry for an extended period of time. Not sure how this could have happened as it is sold as a "maintenance free" item with a 10 year warranty.

The design is not too dissimilar to other well known bearings. The Thorens 124 being a good example.

A steel spindle is press fit into an aluminium platter. There is a captive tungsten ball at the end and a tidorfolon bearing surface underneath. An aluminium bearing housing contains two sintered bronze bushings.
Attached Images
File Type: jpg old spindle crop.JPG (560.2 KB, 1226 views)
File Type: jpg bearing housing crop.JPG (858.8 KB, 1178 views)
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Old 23rd July 2013, 02:08 PM   #2
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Like many turntable brands, the quality of engineering on display isn't that good. can the manufacturer even fix it?
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hoping to pick up some things.
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Old 23rd July 2013, 02:17 PM   #3
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So, after some head-scratching and talking to people who know this stuff i decided against diy repairs or attempting to reuse the platter with a different bearing.

The factory in Germany offered to either sell me a new bearing or replace it themselves. The procedure of removing and refitting the bearing did not sound too appealing and so it went back to the factory.


A new spindle was press-fit and a new matching housing was also manufactured. The old spindle apparently got damaged in the process of being removed.

Well, it came back and much to my horror turned out to be nearly as noisy as the old damaged one. When the platter spins noise can easily be heard a meter away. Or two.


The factory assured me the noise will get better after it spins for a while. And it probably will.

Will it become silent enough for use in a high quality turntable? I don't know.

For one, the spindle looks mat, rather than polished. Tool marks are seen all over. The bushings - well, there is a picture provided. Turns out spindle pictures are not easy to take, especially without dedicated lighting but one can still get the idea.

As for the bushings, my understanding is that one should aim for the correct size by design. Machining may easily reduce the porosity of the sintered bronze and reduce lubrication. This probably explains why the bushings look the way they do - they were machined using some appropriate tool. It also hints at the reason the original bearing self-destructed, but not being the original owner i can only speculate why it died so young.

And as a rather ironic comparison i also include a pic of my Thorens 124 spindle. Not sure about the exact age but has certainly passed its 50-th birthday.

Unlike the Acoustic Signature, the Thorens spindle looks mirror polished and is extremely smooth to touch. Because of the reflections it also much harder to photograph.

Dunno what to make out of this. Not being a machinist or a mechanical engineer i don't know much about these things. Maybe the new bearing will polish itself after working for a couple of thousand hours. Maybe it will self-destroy. Maybe the noise doesn't matter and the tight tolerances are all important. Maybe in the middle of summer there was only an apprentice left running the lathe...
Attached Images
File Type: jpg bronze.JPG (642.8 KB, 1122 views)
File Type: jpg new bearing crop 3.JPG (321.2 KB, 1079 views)
File Type: jpg new bearing crop 2.JPG (393.5 KB, 1059 views)
File Type: jpg new bearing crop.JPG (365.9 KB, 284 views)
File Type: jpg TD124.jpg (387.6 KB, 294 views)
File Type: jpg TD124 crop.jpg (285.4 KB, 284 views)
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Old 23rd July 2013, 02:55 PM   #4
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The new shaft is made from the same steel. It is just brand new. In order to avoid confusion, the last two pics above are of a Thorens 124.

For comparison, the platter weighs more than 10kg and the spindle is 12mm against the Thorens 14mm. Not sure if this is very important.


Irony alert:


http://www.drhifi.net.au/New%20Equip...%20Bearing.jpg

Last edited by analog_sa; 23rd July 2013 at 02:59 PM.
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Old 23rd July 2013, 02:57 PM   #5
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The cross hatching in the bronze bushing is there to retain oil, though they could have used an oilite bronze bearing that doesn't need the hatching. It does appear quite coarse for this application though. The spindle should be polished, though the finish isn't so terrible that it could be a problem. I'd use a heavy oil and run for days to see if it runs in.
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Old 23rd July 2013, 03:00 PM   #6
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Quote:
Originally Posted by analog_sa View Post
The new shaft is made from the same steel. It is just brand new. In order to avoid confusion, the last two pics above are of a Thorens 124.

For comparison, the platter weighs more than 10kg and the spindle is 12mm against the Thorens 14mm. Not sure if this is very important.


http://www.drhifi.net.au/New%20Equip...%20Bearing.jpg
The lateral force on this bearing is insignificant, so not to worry about the shaft being smaller in diameter than the Thorens. The only issue I can see is if there is lateral play in the bearing. There should be none in this application. The platter basically spins on the bearing anyway. The bronze bearing is just there to keep the platter upright.
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Old 23rd July 2013, 03:00 PM   #7
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Smaller shaft will egg out the hole a bit sooner obviously.
The metal may polish itself ... but it may also tear up the other bushing and gall and score itself as that other bushing gets scored.
You may have to keep oiling it and cleaning it and keep a close eye on it.
We have what are called oil light bushings (they take in oil and self lubricate) I put/replace in motorcycles all the time.

I'd think something like that may work. If you can put it in that spot.
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Old 23rd July 2013, 03:19 PM   #8
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Quote:
Originally Posted by srinath View Post
Smaller shaft will egg out the hole a bit sooner obviously.
The metal may polish itself ... but it may also tear up the other bushing and gall and score itself as that other bushing gets scored.
You may have to keep oiling it and cleaning it and keep a close eye on it.
We have what are called oil light bushings (they take in oil and self lubricate) I put/replace in motorcycles all the time.

I'd think something like that may work. If you can put it in that spot.
Cool.
Srinath.
Since the lateral loads are insignificant (unless the platter is unbalanced), the bearing should last a long time. He needs to check for play in the bearing when it is dry. There should be virtually none that he can detect. Since the loads on this bearing are light, I doubt there would be any galling or spalling unless it's run dry.

Changing the oil during the run in period is a good idea. It's a hassle though.

I remember I had a Merrell modified AR turntable many years ago. The bearing he installed was really awesome. This one doesn't look nearly as good.

A plain oilite bronze bushing is a good idea and skip the cross hatching.
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Old 23rd July 2013, 03:24 PM   #9
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Quote:
Originally Posted by dirkwright View Post
The bronze bearing is just there to keep the platter upright.
Yes, but this seems to be the source of noise as well. The polished tungsten ball on the tidorfolon plate cannot make such scraping noise.

Any ideas why the old bearing ended up like that? The bronze did not retain oil and failed to lubricate? The spindle lacked proper hardening? The more i look at this, the more perplexed i get.

Otoh the finish of the platter is first rate. Is modern high-end designed just for looks?
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Old 23rd July 2013, 04:00 PM   #10
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Originally Posted by analog_sa View Post
Yes, but this seems to be the source of noise as well. The polished tungsten ball on the tidorfolon plate cannot make such scraping noise.

Any ideas why the old bearing ended up like that? The bronze did not retain oil and failed to lubricate? The spindle lacked proper hardening? The more i look at this, the more perplexed i get.

Otoh the finish of the platter is first rate. Is modern high-end designed just for looks?
Yes, of course. The noise is coming from the bronze bushing (bearing).

Dealer or owner error I suppose about the previous bearing.

If you know someone who is a good machinist, they can help you make this much better for not much money.
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