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Old 26th July 2006, 01:44 AM   #1
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Default Bearing problems...need some advice

First of all, I'd like to say that I'm really overwhelmed with this forum and how much great help and information I've received on it in the past.

I'm building a diy TT, which, so far is going well. I just got my bearing back from the machine shop today, and am a bit dishearteaned. This bearing consisted of a precison stainless steel shaft with teflon coating, a teflon sleeve pressed into a sleeve of broze, a molybdenium-coated thrust plate, and a ceramic ball. I bought most of these parts to the best precison I could from McMaster Carr, and instructed the shop to do the rest.

This bearing has just barely visible play in it, and a bit of the teflon coating has worn off the top of the shaft, obviously from someone turning it sans lubricant. I was really hoping to get a high-performance turntable out of this project, but funds are running short, so I will have to salvage this project somehow. I will most likely get another shop to make a new teflon sleeve insert and clean up the shaft. I was also thinking though, couldnt this bearing be used with a thick grease, as a desperate measure? I was planning on using a very viscious lubricant in the first place, to provide damping and a bit of resistance, without introducing any extra friction. This would be coupled to a high-torque motor. Dont the garrard grease bearings have extra play designed into them?

Thanks,
Zach
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Old 27th July 2006, 08:17 PM   #2
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Default Re: Bearing problems...need some advice

Sorry to hear the job didn't turn out the way you wanted.
I have a suggestion. Teflon is not a good material to use for a "sleeve". The coefficient of thermal expansion is high and depending on the degree of press fit with the housing, the sleeve could spin on a cold day. On the other side, if you use say a 0.003" pres fit and it does stay put, you would still have clearance issues with the bearing shaft .
Without sounding too arrogant, I have over 30 years machining experience and my reccomendation is to choose another sleeve material.
I would go with brass or Delrin AF, which has Teflon in it.
It has much better thermal expansion qualities and will last longer than 100% Teflon.
Lastly, there should be absolutely no visible play in the bearing for ultimate performance.

Quote:
Originally posted by Capt Zach
First of all, I'd like to say that I'm really overwhelmed with this forum and how much great help and information I've received on it in the past.

I'm building a diy TT, which, so far is going well. I just got my bearing back from the machine shop today, and am a bit dishearteaned. This bearing consisted of a precison stainless steel shaft with teflon coating, a teflon sleeve pressed into a sleeve of broze, a molybdenium-coated thrust plate, and a ceramic ball. I bought most of these parts to the best precison I could from McMaster Carr, and instructed the shop to do the rest.

This bearing has just barely visible play in it, and a bit of the teflon coating has worn off the top of the shaft, obviously from someone turning it sans lubricant. I was really hoping to get a high-performance turntable out of this project, but funds are running short, so I will have to salvage this project somehow. I will most likely get another shop to make a new teflon sleeve insert and clean up the shaft. I was also thinking though, couldnt this bearing be used with a thick grease, as a desperate measure? I was planning on using a very viscious lubricant in the first place, to provide damping and a bit of resistance, without introducing any extra friction. This would be coupled to a high-torque motor. Dont the garrard grease bearings have extra play designed into them?

Thanks,
Zach
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Old 1st August 2006, 03:52 PM   #3
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Thanks for the advice. I've taken the bearing to a different machinist, and instructed him to make a new sleeve, form the Delrin AF as you suggested.
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Old 1st August 2006, 05:43 PM   #4
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Default One more bit of advice....

Advise the machinist to rough the sleeve bore to within 0.030" of finished size, then press fit to the housing followed by final machining of the bore to a close slip fit with the bearing shaft.
I would give him the shaft so he can use it as a gauge.

Quote:
Originally posted by Capt Zach
Thanks for the advice. I've taken the bearing to a different machinist, and instructed him to make a new sleeve, form the Delrin AF as you suggested.
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Old 12th August 2006, 10:04 PM   #5
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in my experiance,...very few machine shops can come close to a linn or thornes bearing

there perseption of close tolerance is hard to gtee on one off bits of work,,and sometimes expensive to find out

i make my own bearings...and it takes so many goes to just get 1 of perfection....and everytime i do it i wish i had just taken the easy option of buyin a secondhand linn or thornes bearing/shaft

hope that helps
best wishes
j7
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Old 12th August 2006, 10:14 PM   #6
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Quote:
Originally posted by AudioOrigami

i make my own bearings...and it takes so many goes to just get 1 of perfection....and everytime i do it i wish i had just taken the easy option of buyin a secondhand linn or thornes bearing/shaft

hope that helps
best wishes
j7

What equipment are you using to make your bearings?
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Old 12th August 2006, 10:24 PM   #7
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hi Vinyl-Addict

i have my own high presion lathe... and a nice mill and,... i have a new cnc mill, ...10 ton press ...and index machine for mill etc...
between them i have a limited ability ...and no time to fiddle..so im not lookin for any work on that side

as i said in last post makeing bearings ...or top class bearings for turntables is very easy to make bad and very hard to be better

when i was very young i managed to get a tour round "castel engeering (the peeps linn use to make the bearings) even at a young age i was totally shocked at the high presion used



any questions just ask and best wishes
j7
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File Type: jpg small bearing parts.jpg (29.6 KB, 250 views)
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Old 12th August 2006, 10:37 PM   #8
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Quote:
Originally posted by AudioOrigami
hi Vinyl-Addict

i have my own high presion lathe... and a nice mill and,... i have a new cnc mill, ...10 ton press ...and index machine for mill etc...
between then i have a limited ability ...and no time to fiddle..so im not lookin for any work on that side

as i said in last post makeing bearings ...or top class bearings for turntables is very easy to make bad and very hard to be better



any questions just ask and best wishes
j7
Thanks for the reply. I was just curious as to why it took several attempts to make a successful bearing. I own and operate a machine shop, manufacturing is my business so no problem with equipment at hand. I agree that designing and making a bearing that will work is quite difficult and having the right equipment for the job is mandatory if success is what you seek.

Internal view of upper housing with tungsten carbide thrust plate, 2 micron finish.
Click the image to open in full size.

Both housings shown-This is obviously an inverted design.

Click the image to open in full size.
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Old 12th August 2006, 10:43 PM   #9
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Hi VA

yes u know how hard it is to gtee perfection with your experience ...

the peeps at thornes knew how hard it is and produced a master piece with thge td160 super

best wishes for now
j7
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Old 12th August 2006, 11:18 PM   #10
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hi Peeps

yes love the thornes turntables and the super bearing is the best they ever made

j7
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