Knife Edge Bearing - Pros & Cons?

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Solist
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Re: Knife Edge Bearing - Pros & Cons?

Post by Solist » 06 Jun 2018 19:45

One of the problems you may encounter with knife edge bearings is that they sometimes wont sit properly. A while ago I have read a thread about SME replacement parts poorly machined which caused the bearing to have 2 contact points instead of a single point (more U shaped instead of V shape for simpler explanation).

Nothing to worry about when buying new, but something I thought worth mentioning.

watchnerd
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Re: Knife Edge Bearing - Pros & Cons?

Post by watchnerd » 08 Jun 2018 14:36

Solist wrote:One of the problems you may encounter with knife edge bearings is that they sometimes wont sit properly. A while ago I have read a thread about SME replacement parts poorly machined which caused the bearing to have 2 contact points instead of a single point (more U shaped instead of V shape for simpler explanation).

Nothing to worry about when buying new, but something I thought worth mentioning.
interesting that when SME re-imagined the 3009 in the form of the new M2-9R, they used gimball bearings.

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Re: Knife Edge Bearing - Pros & Cons?

Post by billshurv » 08 Jun 2018 15:17

There could be many reasons for that though above technical ones.

Solist
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Re: Knife Edge Bearing - Pros & Cons?

Post by Solist » 08 Jun 2018 16:47

Who knows, havent seen many of the M2-9R around for sale.

There was also an SME clone produced back in the days which used gimbal type bearings.
2teslagar.jpg
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watchnerd
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Re: Knife Edge Bearing - Pros & Cons?

Post by watchnerd » 09 Jun 2018 21:13

So it sounds like, generically, there is no simple rule regarding gimball vs knife bearings.

That both have pros and cons.

And it really comes down to the implementation?

Or are those who definitely prefer one vs the other?

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Re: Knife Edge Bearing - Pros & Cons?

Post by tlscapital » 10 Jun 2018 00:12

Coming from the sturdy world of the turntables like the SL-1200's, I never would have believe to end up with a wand just "resting" on knife edge bearing through gravity. Even less so fitted on a wobbly turntable with a platter pulled by a rubber string... That I was "forcefully" lend once my guard was down.

Yet, instantly I fell in love with the different "imprint" in sound it dished out. Got to understand better what was at stake in there with less prejudgements than before and accepted my ear preferences over my mind's beliefs on the matter. Even got to tweak on & in it to full satisfaction and truly improved playback.

If I understand that the uni-pivot takes the idea further on, it will never be suited for my use and need as I play mainly 45's and the swift turnover must be careful but casual to be swift altogether. So the knife edge bearing like the SME I have is my match on the idea/design of the balanced pivot on two contact points.

Unarguably there are much better (higher end) gimbal bearing tonearms out there than the ones I've had to live with prior my unexpected encounter with this now "adopted" SME one. Still, now that I got over the "fear" of the loose factor, I am sonically conquered and converted. Yet open to hear and willing to compare...

To be fair, I understand those who still dislike or feel uncomfortable with the idea of such "loose" devices as I was once one of them. And the fact that the wear on the knife edge bearings is inherent to it's use through time calls for acceptance that "maintenance" if not replacement have to be done occasionally in order to perform accordingly.

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Re: Knife Edge Bearing - Pros & Cons?

Post by antennaguru » 10 Jun 2018 04:39

I have a Lenco tonearm dedicated to a 78 record cartridge, and it has knife edge bearings where the V-Blocks that support the knife edge(s) are replaceable. The original V-Blocks were a soft rubber-like material, and they were worn but easily replaced. I replaced them when I was replinthing and rebuilding that Lenco L75 turntable with replacement V-Blocks that were called "Desmo" which seemed to me like a very carefully machined hard plastic composite material. Brass V-Block replacements were also available. That tonearm now works quite nicely, but not so well with a 33/45 microgroove LOMC as resides on the second tonearm on that enlarged plinth - which happens to be a gimbaled oil damped 12 inch Jelco 750. I do like that the V-Blocks were designed to be replaceable and there are choices.

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Re: Knife Edge Bearing - Pros & Cons?

Post by watchnerd » 10 Jun 2018 08:00

tlscapital wrote:
Unarguably there are much better (higher end) gimbal bearing tonearms out there than the ones I've had to live with prior my unexpected encounter with this now "adopted" SME one. Still, now that I got over the "fear" of the loose factor, I am sonically conquered and converted. Yet open to hear and willing to compare...

To be fair, I understand those who still dislike or feel uncomfortable with the idea of such "loose" devices as I was once one of them. And the fact that the wear on the knife edge bearings is inherent to it's use through time calls for acceptance that "maintenance" if not replacement have to be done occasionally in order to perform accordingly.
I didn't know they wore out....

How is maintenance done on a knife edge?

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Re: Knife Edge Bearing - Pros & Cons?

Post by scho2684 » 10 Jun 2018 10:16

tlscapital wrote:Unarguably there are much better (higher end) gimbal bearing tonearms out there than the ones I've had to live with prior my unexpected encounter with this now "adopted" SME one.
The Jelco knife bearing may look like a similar idea, however its not adopted as Jelco has the knifes on the opposite side, and that is a different approach...

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Re: Knife Edge Bearing - Pros & Cons?

Post by tlscapital » 10 Jun 2018 10:16

watchnerd wrote:
tlscapital wrote:
Unarguably there are much better (higher end) gimbal bearing tonearms out there than the ones I've had to live with prior my unexpected encounter with this now "adopted" SME one. Still, now that I got over the "fear" of the loose factor, I am sonically conquered and converted. Yet open to hear and willing to compare...

To be fair, I understand those who still dislike or feel uncomfortable with the idea of such "loose" devices as I was once one of them. And the fact that the wear on the knife edge bearings is inherent to it's use through time calls for acceptance that "maintenance" if not replacement have to be done occasionally in order to perform accordingly.
I didn't know they wore out....

How is maintenance done on a knife edge?
When I started my tweaks on both my Thorens turntable and SME tonearm, I did a lot of browsing on the net and remember reading a "tutorial" on some other audio dedicated site/forum of a guy having a look with a microscope camera at his SME knife edge bearing V block pivot and in shock saw "in dented" wear.

Now mind you that indeed some of these gears had previous professional use and so intense activity/wear. Should this knife edge bearing V block wear gravely affect the sound is yet to be proven in real and direct comparison. Vaguely I remember the guy DIY'd a piece of V block knife edge bearing 'thrust' replacement...

To what extent such trial is a welcome "renewal" or improvement is something to take with a lot of caution as usual. Especially since the "universal" improvement never exist in audio gear. But I believe that some 'thrust' experiments replacement in the V block could be done instead of the "whole piece" replacement.

First I am finalizing bigger jobs before settling down some and checking in closer in there and venture maybe some in DIY trials if ever. Just like the platter shaft bearing 'thrust' is replaceable on most turntables with such design, the SME knife edge bearing V block could have had a "replaceable" thrust piece there.

But those SME's where not originally thought and designed to be "self-serviced" as such... No matter how much they have a lot of evolutive potential, tweak maneuvers on them require skills, equipment and a lot of know how/understanding as to what is at aim since it can easily turn out to be deceiving instead of rewarding.

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Re: Knife Edge Bearing - Pros & Cons?

Post by billshurv » 11 Jun 2018 01:17

tlscapital wrote:Coming from the sturdy world of the turntables like the SL-1200's, I never would have believe to end up with a wand just "resting" on knife edge bearing through gravity.
You are aware how the vertical gimbal on the SL-1200 is a sharp point pushing onto a ball?

Now I should not that there is a big design flaw with the old SMEs which is that the knife bearings are not aligned with the headshell. There is a company that will fix that and put nice sapphire bearings in. I have not dared ask how much. http://www.true-point.co.uk/tpul-sme-kn ... hase-1.htm

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Re: Knife Edge Bearing - Pros & Cons?

Post by Spinner45 » 11 Jun 2018 02:22

billshurv wrote:
tlscapital wrote:Coming from the sturdy world of the turntables like the SL-1200's, I never would have believe to end up with a wand just "resting" on knife edge bearing through gravity.
You are aware how the vertical gimbal on the SL-1200 is a sharp point pushing onto a ball?

Now I should not that there is a big design flaw with the old SMEs which is that the knife bearings are not aligned with the headshell. There is a company that will fix that and put nice sapphire bearings in. I have not dared ask how much. http://www.true-point.co.uk/tpul-sme-kn ... hase-1.htm
That site's mention of "azimuth roll" are why I never liked tonearms with their misaligned bearings.
Quote:
"When the SME 3009 Series 2 tonearm were manufactured it was not realised that the alignment between the headshell and the knife edge would be so critical in bringing improved listening quality. In later models this was corrected (see SME V above). If the alignment is not correct, then 'azimuth roll' will occur."

Of course, this "roll" is a minimal thing, likely more of an issue with warped records, but who needs that swaying, anyway?
Design the arm with the proper offset vertical bearings in the first place.

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Re: Knife Edge Bearing - Pros & Cons?

Post by tlscapital » 11 Jun 2018 10:56

billshurv wrote:
tlscapital wrote:Coming from the sturdy world of the turntables like the SL-1200's, I never would have believe to end up with a wand just "resting" on knife edge bearing through gravity.
You are aware how the vertical gimbal on the SL-1200 is a sharp point pushing onto a ball?

Now I should not that there is a big design flaw with the old SMEs which is that the knife bearings are not aligned with the headshell. There is a company that will fix that and put nice sapphire bearings in. I have not dared ask how much. http://www.true-point.co.uk/tpul-sme-kn ... hase-1.htm
No, I did not know or see that... but indeed the SL-1200 wand/tube pivot axial's is set at 45° and not at 90° to indeed take better care of the 'azimuth roll' factor. Which can indeed be an issue with the original SME design.

Through my tweaks in conversion into heavy, then heavier and very heavy effective mass, I had to change first for a heavier 'anti-skate' weight and finally for a heavier 'rider weight' ! So I witnessed the physics "action" at work.

Through the last effective mass addition, my low-low compliant cartridge really begin to open-up with tighter bass and much more details in sound. Now I have ask the price of that meaning full 'True Point' knife edge bearing upgrade.

Indeed, on the original SME the 'True Point Upgrade Kit' improvement in sound should be as they advertise; immediate. On their medium effective mass and later light effective mass tonearm the bearings are constantly solicited.

Yet I wonder if, on such a heavy effective mass converted SME tonearm like mine where both horizontal and vertical movements at play are rather brought down now through inertia, this upgrade should be significant...

$ignificant enough I mean. I am not rich and that is exactly why I went first into the DIY tweaks and conversions journey instead of aiming directly at my dream to own turntable and tonearm... in place of my now irreplaceable phono achievements !

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Re: Knife Edge Bearing - Pros & Cons?

Post by tlscapital » 14 Jun 2018 16:09

watchnerd wrote: I didn't know they wore out....

How is maintenance done on a knife edge?
Here's a picture of a polished 'V' knife edge bearing under revision from a SME 3009 MK I tonearm for example.
Capture d’écran 2018-06-14 à 17.01.44.jpg
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watchnerd
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Re: Knife Edge Bearing - Pros & Cons?

Post by watchnerd » 15 Jun 2018 04:54

tlscapital wrote:
watchnerd wrote: I didn't know they wore out....

How is maintenance done on a knife edge?
Here's a picture of a polished 'V' knife edge bearing under revision from a SME 3009 MK I tonearm for example.
Capture d’écran 2018-06-14 à 17.01.44.jpg
I will now expose my ignorance:

Other than some....rust, I guess....it seems like the groove in the middle seems okay.

But I think I probably don't know what I'm looking at.