Saphire bearings at smallparts (XA vertical)

american simplicity
MuZak

Saphire bearings at smallparts (XA vertical)

Post by MuZak » 12 Mar 2009 03:15

Smallparts.com has small sapphire bearings available
that might work in the XA arm... to replace the crummy
delrin (once and for all).

If they'd work, it'd make for a nice upgrade.
Details here

https://images-na.ssl-images-amazon.com ... AA550_.jpg
Those of you with fine measuring tools might be able
to tell if they'd fit.

Details from the web page:
Sapphire Vee Jewel Bearing .0800" / .0803" OD , Angle 85 / 95 Degrees , Thickness .0450" / .0500" , Vee Depth .0200" / .0300"
----------------------------
* Radius .0080 / .0120
* Melting Point 3722 Degrees Fahrenheit
* Specific Gravity 3.98
* Scratch Hardness 9 Mohs
* Compressive Strength 300000 psi at 25 deg Celcius

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Re: Saphire bearings at smallparts (XA vertical)

Post by gkimeng » 12 Mar 2009 03:30

MuZak wrote: Those of you with fine measuring tools might be able to tell if they'd fit.
I take it you're thinking of these for the vertical pivots. You'd probably have to bore out the existing pivot openings and find a way to seat them. But if you manage to get that done, you probably could still use the original conic setscrews. Whether that would get you anything over the originals, I don't know. The real issue with delrin bearings on AR tables is the platter and horizontal pivot bearings.

MuZak

Re: Saphire bearings at smallparts (XA vertical)

Post by MuZak » 12 Mar 2009 05:31

gkimeng wrote: I take it you're thinking of these for the vertical pivots.
Stated in the subject line.
gkimeng wrote: You'd probably have to bore out the existing pivot openings and find a way to seat them.

I would think that just a press-fit would do..
Its not like they're going to take a lot of force.. in any
direction.
Opening them up should be easy enough.
gkimeng wrote: But if you manage to get that done, you probably could still use the original conic setscrews. Whether that would get you anything over the originals, I don't know. The real issue with delrin bearings on AR tables is the platter and horizontal pivot bearings.
Thats easy for you to say...
Mine are a mess.. and many others I've seen were too.
I'm under the impression its a common problem?
The delrin is all chewed up... little bits protruding outwards
too.

As for whether it'd gain anything..
While I personally haven't tested extensively with bearings
for turntables and tonearms...
many expensive/exotic designs use them.
Several thousand dollar arms use sapphire bearings..
The $100. early ARs used delrin.
Maybe its just snake oil.... or..
maybe multi thousand dollar arms are somewhat better
than XA arms.

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Re: Saphire bearings at smallparts (XA vertical)

Post by gkimeng » 12 Mar 2009 06:55

MuZak wrote:
gkimeng wrote: Several thousand dollar arms use sapphire bearings..
The $100. early ARs used delrin.
Maybe its just snake oil.... or..
maybe multi thousand dollar arms are somewhat better
than XA arms.
The question is not whether the multi-thousand dollar arms are better; it's whether putting sapphire bearings into the old AR arm would make it any better.

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Post by solex » 12 Mar 2009 12:47

I cannot tell from the picture but do the bearings have a recess for the cone on the set screw?

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jewel bearings

Post by jdclock » 12 Mar 2009 14:38

i'm glad someone picked up on this topic of jewel bearings from my post on the thread about tonearm bearings. If someone were to contact Bird Precision and maybe send a spare tonearm assembly to their design department, they could probably be very helpful in recomending proper jeweling, whether a vee jewel, ring jewel, size, etc. Their web site is very informative.

http://www.birdprecision.com/bearings/guide.cfm

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Post by gkimeng » 12 Mar 2009 15:05

It listed in the specs of a "V" depth of 20 to 30 thousandths. They probably would work........biggest issue would be perfectly centering them to assure proper azimuth.
I think the idea is to find jewels that would just fit into the existing holes, and I think these may be a bit too big, but I've never mic'ed them and don't have anything here that I could use to accurately measure their diameter. I'll take it to the office with me and see if I can find time to mic it in the lab, but my spare drum is brass, not delrin, so the dimension I get may not be applicable.

My big concern with this idea is that azimuth would never be any better than the alignment of the original holes, which from Greg's description of his arm are bored into delrin rather than brass like the later models and are, according to his description, "chewed up." Having the setscrew points riding in the center of two "V" jewels set into this part may exacerbate any misalignment in the old, damaged part more than having them riding on the bottom of a larger hole.

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Re: jewel bearings

Post by gkimeng » 12 Mar 2009 19:11

jdclock wrote:i'm glad someone picked up on this topic of jewel bearings from my post on the thread about tonearm bearings. If someone were to contact Bird Precision and maybe send a spare tonearm assembly to their design department, they could probably be very helpful in recomending proper jeweling, whether a vee jewel, ring jewel, size, etc. Their web site is very informative.

http://www.birdprecision.com/bearings/guide.cfm
The straight hole ring might be a better choice for this. Running the conic setscrews into holes as in the original design rather than vees would make adjustment less finicky.

MuZak

Re: Saphire bearings at smallparts (XA vertical)

Post by MuZak » 12 Mar 2009 21:56

gkimeng wrote: The question is not whether the multi-thousand dollar arms are better; it's whether putting sapphire bearings into the old AR arm would make it any better.
No, the question IS... what makes ANY tonearm
better.

"Better" arms have better bearings.
Arms with better bearings, are better arms.

I'm thinking of trying to improve other aspects
of the AR arm as well.
(Something not uncommon on these boards, while
reassembling after cleaning and maintanance/repair.)
To (hopefully) improve it *in the aggregate*,
to whatever degree.

Besides.. its my question. ;-p

MuZak

Post by MuZak » 12 Mar 2009 22:15

Note that on the webpage, it mentions (IIRC) that
the jewls require further polishing... IE: finishing.
They appear to be merely concave.

That finishing work might render them to costlly
for the purpose.

jdclock's birdprecision suggestion makes the most
sense IMO.
Their cost estimate is, I guess, what would tell
the tale.
"The bottom line is the bottom line."

I'm gonna have a good look at that birdprecision
site when I've more time this evening for knowledge
sake.
LQQks real interesting.
I think the idea is to find jewels that would just fit into the existing holes, and I think these may be a bit too big,
I would think that just opening them verrrry slowly
and carefully with a T-reamer would be ok...
at least if you've a spare drum..
but my spare drum is brass, not delrin, so the dimension I get may not be applicable.
There were ALL delrin drums???
I've only seen the kind that are brass with small
holes filled with (what seems like) delrin tubes.
his arm are bored into delrin rather than brass like the later models and are, according to his description, "chewed up
I'll try to take and post a pic of mine this evening.
It'll show both what its made of and its condition

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Post by gkimeng » 12 Mar 2009 22:33

MuZak wrote: There were ALL delrin drums???
I've only seen the kind that are brass with small
holes filled with (what seems like) delrin tubes.
[
I've heard cites that there were, but have never seen them. I've never seen a brass drum with delrin tubes, either. All the drums I've seen have been all brass. I'll snap a pic of a spare I have at home and post it tonight.

MuZak

Post by MuZak » 12 Mar 2009 23:06

gkimeng wrote: I've heard cites that there were, but have never seen them. I've never seen a brass drum with delrin tubes, either. All the drums I've seen have been all brass.
Wow.. interesting.
I've never seen all brass drums nor even heard of
them.
But it does explain my confusion in certain cases,
when hearing them discussed.
I'll snap a pic of a spare I have at home and post it tonight.
Yes.. thanks... please do.
I'll do the same.

PS: I only realized relatively recently that they're
tubes.
For years I thought it was solid pieces of delrin
(or the like) that took their shape when the conicals
were forced in at the factory.
(then backed off a turn or portion thereof)

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tonearm bearings

Post by jdclock » 13 Mar 2009 00:00

While on the subject of jeweling, i came across another old article on modifying the ar tonearm that i'd never seen before, and this might be a place to substitute jewel ball bearings in place of steel ones. I'm not an engineer, so i'd be interested to hear what someone with that background has to say on this mod (as well as substituting jewel balls for the existing steel ones). Here's the site for the May 1975 issue of The Speaker, the newsletter of the Boston Audio Society. the article on ar tonearm mods starts on page 15.

http://www.bostonaudiosociety.org/pdf/b ... 8-7505.pdf

I don't think the jewels are really very expensive, and it should be fairly easy to push out(or drill out) the delrin rod from the brass hub, and resize the hole for the jewel. Jewels are also available mounted in a brass or steel fitting that's threaded. so that might be an easy fit.

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Post by gkimeng » 13 Mar 2009 00:36

MuZak wrote:
gkimeng wrote: I've never seen all brass drums nor even heard of
them.
But it does explain my confusion in certain cases,
when hearing them discussed.
Turns out I was wrong. The spare piece I have does have delrin inside, it's just so thin that I didn't notice it. This has been in my spare parts box along with an extra arm for some time, and I've never had to use either so I never took a really close look at it. Sorry about that.

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Re: tonearm bearings

Post by gkimeng » 13 Mar 2009 00:58

jdclock wrote:I'm not an engineer, so i'd be interested to hear what someone with that background has to say on this mod (as well as substituting jewel balls for the existing steel ones). Here's the site for the May 1975 issue of The Speaker, the newsletter of the Boston Audio Society. the article on ar tonearm mods starts on page 15.
I've seen this one before, and it interested me for a bit because they refer to modified arms working successfully with the ADC XLM and I've had no problems running XLMs on the stock arm (though I have XLM IIs and IIIs, which are not quite the massively high-compliance pickups the XLM I was).

On one of my tables I'm using tungsten carbide balls in both the platter (I had to shorten the spindle to use a later XA platter on an earlier TT subchassis, so a new ball was needed), and in the arm, which was missing its ball when I got it. At Mohs 8.5-9, tungsten carbide is harder than the original steel balls that were stock to the table (Mohs 4-5 for plain steel, 7-8 for hardened, I don't know which the originals are), and is almost as hard as sapphire (Mohs 9-9.5); I haven't noticed any difference in the sound between this table and its mate, which is 100% all stock parts.

I wouldn't be too concerned about unpolished vee jewels. Point contact with the conic setscrews isn't going to involve much jewel surface area. The bigest concern will still be getting the jewels properly aligned with each other.

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