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Old 12th September 2011, 01:04 PM   #101
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Straight Tracker View Post
For all I know, that may be how everyone is doing it. But as I said, I've never looked at the underside of a unipivot tone arm.
basic principle of unipivot

personally I think full adjustability in all directions is essential

the uni pivot bearing point itself is the easy part
that's the beauty of the principle

note that there is room for thick grease to dampen
thats the Hadcock trick

please note that I have not seen any of the new Hadcock versions
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File Type: jpg uniipivot.JPG (24.5 KB, 161 views)
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Old 12th September 2011, 01:51 PM   #102
Nanook is offline Nanook  Canada
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Default the three ball solution...

small bearing assemblies such as these have been used forever (or so it seems) in audio. I have a bunch of old tonearms in pieces that use three or four capative balls in a metal carrier. If the "needle point" is not the correct angle it can bind.
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Old 12th September 2011, 02:52 PM   #103
carolus is offline carolus  Belgium
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Quote:
Originally Posted by Straight Tracker View Post
As promised, here is my unipivot suggestion ...... I used 1/8" balls because they are easier to find ....The balls could be carbide or some semi-precious stone ....
Ralf
FYI,
I did (in 2005) a minute montage (DIM) with 3+1 balls (cinematic-bearing) ...
Balls are 3mm from the rear-pignon-ricing-bicycle (Eddy Merckx) ...
And it's work,
Karel
Attached Images
File Type: jpg KINEMATIC TONE ARM 001.jpg (75.3 KB, 153 views)
File Type: jpg KINEMATIC TONE ARM 007.jpg (58.7 KB, 154 views)
File Type: jpg KINEMATIC TONE ARM 010.jpg (49.9 KB, 153 views)
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Old 12th September 2011, 08:29 PM   #104
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that last photo tinitus posted.. thats EXACTLY the impression i had that the unipivot bearing had to be, the pin had to be a sharper point than the pocket itself to allow the arm to tilt up and down for moving it into place, and playing warped records

to keep center of balance low, my idea was to cut the weights out of hardwood in oval shapes with the hole off-center towards one end to slide onto the end of the tonearm shaft

is there some kind of formula to determine the arm length and the angle of the head?... id like to model the 3 ball idea, the idea ive been having was to drill an oversized hole... glue into that hole a metal sleeve to protect the really soft wood which at this point is looking like itll be balsa, glue into the end of the unipivot channel a magnet to held hold the bearings in place, put the three bearing balls in there... and then continue with my idea of cutting off the head of a screw and sharpening it to a point to use as a height adjustable pin

for the balsa tonearm right now im thinking of making it rectangular in cross-section, with a strip of carbon fiber glued across the top side for rigidity and strength, while the balsa maintains its ability to absorb the vibrations... if i know what the length of the tonearm beyond the point of pivot had to be overall, how far from the pivot point the head angles, and what that angle is, i could model this entirely and see what i get
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Old 12th September 2011, 09:31 PM   #105
tinitus is offline tinitus  Europe
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just so that you know, ball bearings are the worst
bushings are way better
though, ball bearings may be convenient if there is any end play to deal with
but if its possible to use bushings, its way better

its all them moving parts
a uni pivot point 'bearing' is almost like no bearing at all

but both pivot point and cup needs to a very precise match
or else you will get 'play' movement


well, I can just as well show whats spinning around in my head right now
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File Type: jpg Peripheral double pivot arm.JPG (15.1 KB, 136 views)
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Old 12th September 2011, 10:24 PM   #106
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well, that looks like it would work... especially if you used atleast a center punch for the tip of the pin to set in so it doesnt slide around.. i like the idea of using a few balls inside the hole with the screw adjustable pin for height... for the screw with the head cut off and sharpened to a point, id also thread a nut and rubber o-ring on so it can be tightened against the threaded bushing on the table so it doesnt work its way out over time

however, 3 balls, or one of those saffire vee bearings seem like it would work just fine.. i would drill a hole large enough for the balls, or the vee bearing... with the balls i could just drill a hole larger than the pin, glue a magnet into the top of the cup, then drop the 3 balls in and the magnets force should automatically flatten them against the top of the cup and hold them in place...

i dont think i would need to glue a piece of tubing inside to strengthen the wall, but atleast glue a metal bushing over the mouth of the cup so that the pin has something to rest against without damaging the tonearm material itself... i think the entire unipivot contraption could probably be done for $0.50-$1.00 from my local hardware store, with a little extra for the piece of balsa, a strip of carbon fiber to glue to the top of it to maintain rigidity (so the balsa doesnt bend over time) and a cartridge

should i carve the headshell as part of the tonearm, or drill a hole in the end of the tonearm to glue in a threaded bushing so i can attach those removable universal headshells?
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Old 12th September 2011, 10:27 PM   #107
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another idea i had for a tonearm was to use a piece of balsa dowel rod... run it through my table saw to cut a groove along one edge for the wiring and then glue it inside a piece of carbon fiber tubing for shape and structural support while maintaining the vibration absorbtion properties of the balsa, has anyone considered something like that?
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Old 13th September 2011, 07:55 AM   #108
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Default Hello tinitus

Quote:
Originally Posted by tinitus View Post
basic principle of unipivot

the uni pivot bearing point itself is the easy part
that's the beauty of the principle
I don't believe that existing unipivot tone arms actually use a pin in a hole with a sharp point.

While it is easy to machine a pin with a sharp point, it is not easy to machine a hole with a sharp point at the bottom. All tools wear the first time they are used. that means, by the time you drill the tenth tone arm, you don't have a sharp point anymore.

I think that manufacturers drill the hole as sharp as they can and then machine a small radius on the mating pin so that the pin will always ride on the tapered part of the hole and never in its point.

I've attached two drawings scale 10:1 and 20:1 to illustrate my point. (no pun intended)

Sincerely,

Ralf
Attached Files
File Type: pdf UNIPIVOT_WITH_RADIUS_SCALE_10_TO_1.pdf (9.3 KB, 42 views)
File Type: pdf UNIPIVOT_WITH_RADIUS_SCALE_20_TO_1.pdf (11.6 KB, 32 views)
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Old 13th September 2011, 08:27 AM   #109
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those PDFs look a tad backwards, in those you have the hole being perfectly sharp but the pin not being perfectly sharp.. surely its easier to sharpen the pin.. however, with weight riding on it i doubt itll stay sharp for long which leads me to believe 3 bearing balls and a pin would probably be the best idea.. but will the arm move smoothly?

how long does the tonearm need to be, and what angle does the headshell need to be at?.. whats the purpose of the angle and which part of the record am i trying to reach... anyone have a good schematic of a pre-existing tonearm i could use?
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Old 13th September 2011, 11:42 AM   #110
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by AnimusDivinus View Post
... which leads me to believe 3 bearing balls and a pin would probably be the best idea.. but will the arm move smoothly?
now that think about it, I think the hadcock actually did use a small ball bearing

btw, maybe you could use a wolfram tig welding electrode for the pin

I would use a sharp punch to make the counterpart cup
if it wears out ? hey, its DIY
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