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Since we were talking about PLT tonearms

59.167.188.236
Posted on October 25, 2012 at 22:32:00
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 PLT = Pivoting Linear Tracker.

I've been playing with this concept a while, here's one of my efforts. As you can see this is a proof of concept prototype made with bamboo sticks and scavenged bearings. I would have used better bits for the next version if I hadn't come up with a different design which I like much more.



For JE: you don't even need an alignment jig. I blue-tacked a pointer to the headshell at 90 degrees to the cantilever. It points directly over the spindle at 60mm radius:



And also at 150mm radius, and all points in between to within 0.1mm.



BTW the data on these pic files says they are over three years old, so obviously I'm not going anywhere with them. Anyone who wants to use the ideas can.

Your problem will be bearings. The main bearing in the phot is the head drum out of a VCR. The secondary bearing (hidden under the arm at the end) came out of a failed HDD. Neither are good enough for theis application but obtaining the correct bearings has eluded me for years.


Mark Kelly

 

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Very Interesting! Thank you...., posted on October 25, 2012 at 23:02:49
John Elison
Audiophile

Posts: 24045
Location: Central Kentucky
Joined: December 20, 2000
Contributor
  Since: January 29, 2004
 You might want to talk to Frank Schröder about bearings. He claims his bearings have zero friction. I asked him if his arm would deflect downward if he balanced it and dropped a tiny piece of paper on the headshell. He said it would deflect downward if he dropped a single human hair on the headshell. I don't know if that is actually true, but he seems to have found some very low friction bearings.

Thanks for posting your pictures. It's an interesting design.

Best regards,
John Elison

 

RE: Since we were talking about PLT tonearms, posted on October 25, 2012 at 23:28:46
caligari


 
The guiding mechanism using the bamboo sticks makes me think of using a bearing idea like the Simon Yorke arm with teflon sleeve over the vertical post.

I assume the arm concept is similar to the 1969 Birch patent that we discussed in another forum? Thanks for the pictures.

 

Guide friction, posted on October 25, 2012 at 23:44:21
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 Since there is very little force on the guide mechanism, there is very little friction. If I developed this further I would probably mount a miniature radial bearing on the guide post to reduce this further.

Amongst the many blind alleys while developing these ideas, I had one which used a ferrofluid magnetic linear bearing instead of the guide mechanism you see. I even learnt how to make my own ferrofluid. If you've ever played with ferrofluid you know it gets on everything and is very hard to get off, so you can imagine my wife's reaction to me cooking up ferrofluid in the kitchen. That also killed the idea - I just couldn't imagine anyone letting that stuff anywhere near their precious records.


Mark Kelly

 

Bearings, posted on October 25, 2012 at 23:47:18
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 I've asked everyone I know to try to obtain the bearings I want but so far to no avail. They are stainless pivot bearings, made by NSK Micro in Japan.

Jonathan Carr of Lyra was going to ask the manufacturer directly but haven't heard anything back.


Mark Kelly

 

RE: Bearings, posted on October 26, 2012 at 08:50:50
dtut
Audiophile

Posts: 119
Location: central coast california
Joined: March 27, 2006
 Mark,

Interesting concept. Thanks for posting them. Frank Schroeder mentioned hybrid ceramic bearings. Have you tried them or full ceramic?

John,

Thanks for posting the graph above.

For LT alignment, a strip of graph paper or of something like a calendar page with a spindle hole at one end works just fine. With the arm set up so that at any point, the stylus point is on the radial line with the cantilever perpendicular to it and tangent to the groove, it will be the same at any other place across the record.


Doug

 

RE: Bearings, posted on October 26, 2012 at 09:54:21
directdriver
Audiophile

Posts: 2
Joined: October 25, 2012
 Mark Kelly: "They are stainless pivot bearings, made by NSK Micro in Japan."

Is this what you're talking about?

 

RE: Bearings, posted on October 26, 2012 at 10:30:23
dtut
Audiophile

Posts: 119
Location: central coast california
Joined: March 27, 2006
 DD,

I don't know if that will help Mark, but I thank you.


Doug

 

Dat's der bunny, posted on October 26, 2012 at 15:19:23
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 Yes, those are the bearings I want, specifically BCF-9 and BCF-6.

As far as I can find, they are not obtainable anywhere.




Mark Kelly

 

RE: Dat's der bunny, posted on October 26, 2012 at 17:17:56
Tre'
Industry Professional

Posts: 17963
Location: So. Cal.
Joined: February 9, 2002
 You can't buy them from the manufacture?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

Tried and failed., posted on October 26, 2012 at 17:42:54
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 As mentioned, I've approached the manufacturer twice with no luck. Jonathan Carr of Lyra very kindly wrote to them on my behalf in Japanese. Still no luck.

I've tried the Australian and US distributors for NSK. Same result.

I've tried a couple of specialist Defence procurement agencies (there are a couple of mil-spec uses for these things so they have procurement IDs). Same result.

I'm starting to believe they are vapourware.




Mark Kelly

 

While not a pivot bearing, posted on October 26, 2012 at 21:48:47
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
 couldn't you simply use an ABEC 7 or 9 sealed bearing and machine a pivot. Shouldn't cost very much.

The original linear arm that Clearaudio bought the patents for, used even lower tolerance bearings and achieved some unbelievable tracking. I remember when he demoed the arm by playing a record with the spindle hole drilled half inch off center and the arm tracked well although there ws obvious wow from the changing speed of the disc.

Stu

 

Nope., posted on October 26, 2012 at 23:12:37
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 Contact angle is wrong.

The contact angle needs to be about 30 degrees (60 degrees included angle).
F contact / F load = 1 / sinθ so for 30 degrees F contact is 2 x F load.

A typical radial bearing has a contact angle around 10 degrees so F contact = 6 x F load. Since the capacity of the bearing is determined by F contact, the radial bearing needs to be much larger for a given axial load.

Since the friction is dependent on size and F contact, it will go up by even more, figure times 6 to 8.


Mark Kelly

 

Mark, Timken also produces pivot bearings., posted on October 27, 2012 at 01:17:55
hagustos
Audiophile

Posts: 212
Location: Izmir
Joined: August 6, 2002
 Look for "pivot bearings type PR for closed back, type A for open back"

Here is the picture taken from their pdf catalogue:







Regards,

Hakan

 

Yep, also unobtainium, posted on October 27, 2012 at 01:41:17
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 I went for the NSK first because they are the OEM spec bearing in the Dynavector DV-50X arms that I am rebuilding into PLTs.

I could substitute Timken S6A7B and S5PR with a bit of extra work but I have been unable to obtain them either.


Mark Kelly

 

Maybe you should ask Hadcock UK tonearm manufacturer, posted on October 27, 2012 at 02:24:55
hagustos
Audiophile

Posts: 212
Location: Izmir
Joined: August 6, 2002
 where they find them.
AFAIK they are still using that kind of bearing for their unipivot tonearm bearings.

Regards,

Hakan

 

Oxymoron, posted on October 27, 2012 at 02:54:32
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 Unipivot and cardanic bearings are an oxymoron.


Mark Kelly

 

The testy tone, posted on October 27, 2012 at 03:11:25
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 Sorry for the testy tone of my responses.

I recognise that everybody is trying to help but the suggestions that have been made so far are all things I'd already thought of.


Mark Kelly

 

They really used one pin and 4 ball in a cup bearing set for their unipivot tonearms ..., posted on October 27, 2012 at 09:00:27
hagustos
Audiophile

Posts: 212
Location: Izmir
Joined: August 6, 2002
 I don't know if they changed the design or not.
I remembered because designer was saying he prefered 4 ball over any other number and talked about the benefit of avoiding any extensive rolling movement which is good for the handling of tonearm.
I even tried that in a homemade unipivot with pivot bearing from a Garrard tonearm and it worked just fine.(pin was facing upwards and four ball cup attached to the tonearm).
I didn't say it is technically good or not I just only wanted to help you by showing an address.

Regards,
Hakan

 

OK thanks I didn't know that, posted on October 28, 2012 at 00:32:10
Mark Kelly
Manufacturer

Posts: 7177
Location: Willy, VIC
Joined: February 28, 2002
 I will look into it.


Mark Kelly

 

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