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Old 11th January 2006, 07:30 PM   #21
pixpop is offline pixpop  United States
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That's exactly what I'm working on. I started this thread just to make sure I was on the right track, and that there wasn't something inherently bad about direct drive that would make the whole thing pointless. Apparently, there isn't.

The only thing I can't control is the quality of the original bearing. It may be possible to retrofit the motor onto a quality bearing if that becomes an issue.
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Old 11th January 2006, 07:49 PM   #22
DaveM is offline DaveM  United States
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That was my idea, I have access to a machine shop with grinding equipment as well. I will probably buy a high polished shaft from McMaster Carr and fit that into an oil-lite (brass impregnated with lubrucant) bushing that I will grind to fit the shaft with minimal clearance. Then press in a polished carbide steel ball riding on a thin piece of teflon in an oil bath. I know it would be rediculous overkill, but that would be what I am after.

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Old 11th January 2006, 09:00 PM   #23
EC8010 is offline EC8010  United Kingdom
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Teflon can't take that point loading. But sapphire or diamond can.
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Old 12th January 2006, 07:46 AM   #24
dice45 is offline dice45  Germany
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Default Teflon does make a stable trust plate ...

.. i must know it since my homebrewn TT's platter bearing has a ruby ball of 3mm dia and a teflon trust plate. And one trust plate lasts for more than 5 years. Platter weight is about 4kg .

The trick is that the ball is a calibration ball with extremely low form deviations and ultra-low surface roughness. Any steel ball would eat itself thru the teflon within weeks.
With the ruby ball, there will be a stable indentation in the teflon surface.

And you have heard that thing, too, EC8010, as we met at the ETF in Langenargen 2004. My TT was the one with the fancy modified Rabco tonearm on it. You remember?
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Old 12th January 2006, 08:00 AM   #25
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I read somewhere that the VCR head was the highest precision component in mass production.

I suspect that the hardest part of building a DD is keeping that magnetic field out of the cartridge.
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Old 12th January 2006, 08:29 AM   #26
maxro is offline maxro  Canada
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Quote:
Originally posted by davidsrsb
I suspect that the hardest part of building a DD is keeping that magnetic field out of the cartridge.
An aluminum platter makes a great diamagnetic shield.

Although, I have read that Grado carts don't work well with some tables for lack of sheilding. My dad had one on his direct drive KD-500 and had no issues. Ironically, if I recall, the problem is with Regas (belt drive) and Grado cartridges. Hmm...

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Old 12th January 2006, 09:03 AM   #27
EC8010 is offline EC8010  United Kingdom
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Default Re: Teflon does make a stable trust plate ...

Quote:
Originally posted by dice45
The trick is that the ball is a calibration ball with extremely low form deviations and ultra-low surface roughness. Any steel ball would eat itself thru the teflon within weeks.
Well, well. I live and learn. That's very interesting. Presumably, it also has to be very accurately centred.

Sadly, I remember the Rabco but not the turntable it was on.
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Old 12th January 2006, 09:15 AM   #28
Shaun is offline Shaun  South Africa
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I have a spare SP10 Mkii with what appears to be a worn bearing (the platter rocks). It would be interesting to see what you guys come up with as a bearing to mate to this motor, as I have been told that it's not possible to replace the bearing on this unit.
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Old 12th January 2006, 10:15 AM   #29
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Hi

Why not use the alu plate as a DD Lenz motor ? Only a bearing and a plate. No magnets, only two C-core electro magnets and some control electronics.

Best regards Kim
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Old 12th January 2006, 12:28 PM   #30
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by Shaun
I have a spare SP10 Mkii with what appears to be a worn bearing (the platter rocks). It would be interesting to see what you guys come up with as a bearing to mate to this motor, as I have been told that it's not possible to replace the bearing on this unit.
Perhaps the bearing is dry? If you take it apart a bit, you will find that you can clean the bearing and oil it.

I'd say it would be difficult to replace the bearing, but not impossible.
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