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Old 3rd April 2003, 09:02 AM   #1
peterr is offline peterr  Netherlands
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Default Unipivot principle

Triggered by the recent threads on unipivot-arms I have been thinking about the actual pivot point.
In principle it looks like nr.1 in the drawing below: a cup resting on a perfectly sharp pin. But I assume that in practice it looks more like nr.2: both pin and cup wil not be perfect.
This makes me wonder if something like nr.3 using one ball might be a better solution?

Am I right in my assumptions?
Has this been done before?
Does it/should it work?

Please comment.
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Old 3rd April 2003, 11:22 AM   #2
AuroraB is offline AuroraB  Norway
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As to your sketch #3,--
one ball resting atop of 3 balls i a lower cup has been suggested in another thread, last year sometime....
Sapphire and ruby balls are rather cheap at Smallparts Inc., I beleive.???
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Old 3rd April 2003, 08:39 PM   #3
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Default 4 Ball Pyramid

Yup, the 4 ball pyramid (always self centering, no chatter, low wear and still low friction) is used by Wilson Benesch in their unipivots and it was the approach i used fro the pivot of my own DIY.

I got 4 ruby/sapphire ball bearings 1/8 of an inch in diameter, mounted one on a brass thrust plate to bolt to the arm housing and 3 in a cup machined into the top of the arm pillar.

Bearing housing and arm are shaped from rosewood, arm tube is a 1/8 square brass tube set into the side of the arm wand, counterweight and stub are brass as is the thrust plate, arm pillar and base. Headshell is aero grade high tensile aluminium.

As yet I have not wired it up, fitted side weights or antiskate.

I'll try to get some photos for you soon.

Drew
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Old 6th April 2003, 08:02 AM   #4
EC8010 is offline EC8010  United Kingdom
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Default Cheap source of precision bearings.

Ball point pen tips are high precision, small bearings. Consider, the fit of the ball in the socket is so precise that a metered quantity of ink flows through the gap.
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Old 12th June 2006, 12:26 PM   #5
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Default Re: 4 Ball Pyramid

Quote:
Originally posted by DrewP
Yup, the 4 ball pyramid (always self centering, no chatter, low wear and still low friction) is used by Wilson Benesch in their unipivots and it was the approach i used fro the pivot of my own DIY.

I got 4 ruby/sapphire ball bearings 1/8 of an inch in diameter, mounted one on a brass thrust plate to bolt to the arm housing and 3 in a cup machined into the top of the arm pillar.

Bearing housing and arm are shaped from rosewood, arm tube is a 1/8 square brass tube set into the side of the arm wand, counterweight and stub are brass as is the thrust plate, arm pillar and base. Headshell is aero grade high tensile aluminium.

As yet I have not wired it up, fitted side weights or antiskate.

I'll try to get some photos for you soon.

Drew
...any photo, yet?

Stefano
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Old 12th June 2006, 02:18 PM   #6
too299 is offline too299  Singapore
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Default Re: Unipivot principle

Quote:
Originally posted by peterr
Triggered by the recent threads on unipivot-arms I have been thinking about the actual pivot point.
In principle it looks like nr.1 in the drawing below: a cup resting on a perfectly sharp pin. But I assume that in practice it looks more like nr.2: both pin and cup wil not be perfect.
This makes me wonder if something like nr.3 using one ball might be a better solution?

Am I right in my assumptions?
Has this been done before?
Does it/should it work?

Please comment.
It does not matter which of the application you apply as long as the contact point is precisely matched. Which mean it must cross the Hi-Fi News track(side 1 band 8) without distortion
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Old 11th July 2006, 04:19 AM   #7
mosin is offline mosin  United States
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Although Wilson and others use the pyramid bearing, it was first used in the Magnepan Unitrac tonearm. The information on it that can be downloaded from the Vinyl Engine is a very good read.
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