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Old 4th June 2013, 09:56 PM   #1
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Default The Good Turntable

I am still searching for the right ring magnets. This one may be too strong and the smaller one is too week.
Ringmagnet Ř 70,0 x 30,0 x 10,0 mm N42 Nickel - magnet-shop.net
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Old 5th June 2013, 12:13 AM   #2
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If you want to wait until there are enough numbers to justify the magnets I could contact my Chinese supplier and see about a magnet for this application. I am about to do that for the dome tweeter I am working on now that I finally got my beryllium domes to develop my tweeter. Are you going to use the magnet for levitation?

Steven
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Old 5th June 2013, 07:43 AM   #3
Calvin is offline Calvin  Germany
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Hi,

Joachim wrote:
Quote:
The bearing is simply a teflon cylinder with a teflon mirror. The are 3 set screws on the top and 3 set set screws down in the cylinder.
The spindle is from polished steel with a rounded end that runs on the teflon mirror.
Years ago, I had tried to build a TT from scratch, using a 6kg weighing aluminum platter. As radial bearing I used prefabricated bushings made by Igus (brand name Iglidur something). Igus is well known as manufacturer of bearing plastics which may be used without lubrication.
On paper everything looked really well. Rather low tolerances and rather soft and common steel for the bearing shaft. After description the shafts surface needs to be soft and slightly rough, since the bushing ´rubs´ off the microscopic peaks whilst the running-in period and uses the rub-off as lubricating grease.
The vertical bearing was inverted with a ceramic ball fixed to the platter and a ceramic mirror sunk into the top of the spindle, so that a small oil reservoir formed for lubrication purposes.
I´m not eyactly sure why, but I never got convincing results, but I assume the main drawback was due to the dry running radial bearing beeing noisy.
Maybe also the combination of hard ball - hard mirror was not optimal.
Anyway, I have certain doubts about the useability of dry running radial bearings and polished surfaces on soft plastics.

Another rather unusual idea dealt with the construction of the ´plinth´.

I used tube connectors one finds with furniture and exhibition systems like here: http://diessnergmbh.de/pdf/Katalog57.pdf. One can find these connector systems on ebay in chrome, gold, brushed aluminum or niro-steel. Color and material of the tubes after one´s fashion.
These globe-connectors consist of two claws pressed together by a single screw, that can connect 2 or three tubes perpendicular to each other.
This alows for a very simple setup consisting of two tubes in a T-connection, with the bearing shaft at its centre using a single 3-claw.
Besides end stubs at the tube ends forming the feet, one of the tubes held another claw (2-claw) to mount the tonearm (since the tubes OD may be 25mm, a 23mm Rega pillar will fit). Cost of such a setup is close to ridicolously low. In the end the setup looked a bit like the Kuzma Stabi.

jauu
Calvin
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Old 5th June 2013, 09:30 AM   #4
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Old 5th June 2013, 10:31 AM   #5
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One good behaviour of steel on teflon is that the static friction coefficient equals the sliding friction coefficient (both 0.04 with or without grease) and thus you don't have stick slip effect. Thats the basic idea of using a polished steel axle (which is easily available) and teflon "bearing".
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Old 5th June 2013, 04:48 PM   #6
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Default DIY PTFE Dry Bearing

This is an experimental dry bearing I made at home. The goal was to design and build an excellent turntable bearing from scratch using standard tools that can be found in an average hobbyists workshop. You don't have to worry about fittings and tolerances because it is an adjustable bearing.

For some parts I used a mini lathe, but you can also do it without. The bearing consists of a polished steel shaft that is guided by six PTFE screws. Axial forces are carried by a PTFE plate.
The shaft is rounded and polished at the lower end using a lathe and a rasp/file. You can also use a drill press instead of a lathe to rotate the shaft while filing. Polishing was done using a bench grinder with a felt polishing disc.
It can be a challenge to get PTFE screws in small amounts (< 100 000), so I decided to make them by myself: I purchased a 5mm PTFE rod and cut an M4 thread with an ordinary threading die. After cutting the rod into pieces of the desired length, I rounded one side with file and drill press. The other side was simply slotted using a miniature cutting disc.

The bearing was not used in a turntable yet, but some audio enthusiasts looked at it at the Frickelfest. It works quite good, very silent and free of backlash. I don' have any experiences regarding long term stability, but I think the worst thing that can happen is that you have to replace the PTFE plate or the screws.

Dominik

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Old 5th June 2013, 05:05 PM   #7
MiiB is offline MiiB  Denmark
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Nothing beats an oil film for noise performance, if you aim for Mag-lev, then please consider that the Neo magnet are far from homogenous, and if you use repelling magnets you are bound to get wobbling forces on your bearing.

sorry, no free lunch..

An optim could be to use a sleeve of oil-impregnated PA (Nylon) as an inner-sleeve in a bearing design (oil lubricated), Weight can be supported by ceramic-ball on a polished ceramic disk. support should be as hard as absolutely possible. then you get a singe point of rotation with no compression and low low noise. (this is the hard part of the bearing, any misalignment and you're in trouble)
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Old 5th June 2013, 07:15 PM   #8
ahaja is offline ahaja  Poland
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Maybe here: NEOTEXX m@gnete

I have a few neomagnets 32x16x3 which should be OK for platter 3-5kg.
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Old 5th June 2013, 09:11 PM   #9
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MiiB,
I agree that an oil bearing would probably be the smoothest besides an air bearing but not sure that the friction of teflon would be a real problem at the speeds you would be turning with little to no sticksion between surfaces. Besides that you can use oil on Teflon and I don't think that there is any chemical attack, it would just be a little excessive I would think. As far as the magnetic levitation I would doubt very much that you could detect any variation in magnetic repulsion that would cause a wobble, the energy would be very much equal around the magnet and it would also average over the surface. I think the quality of the magnetic powders are more homogeneous that what you are stating.
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Old 5th June 2013, 09:57 PM   #10
MiiB is offline MiiB  Denmark
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I know this for a fact as I use thousands of Neos every year... It's not so much the powder as it is the fact that they magnetise a lot at the time, and the magnetising Flux varies over the area. And trust me it wobbles, but There is a good way to overcome that problem... Use attraction instead of repulsion. then you can insert iron disks, they will then distribute the force equally

I would for sure use Oil in a teflon bearing.

Last edited by MiiB; 5th June 2013 at 10:01 PM.
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