Turntable bearing question.

Arckivio

Member
2012-12-28 11:09 pm
Hi everyone. I'm new to the forum, apart from the time it took me to read every page of the picture gallery in the valve amps section. It's amazing what some people can build!!! This is my first thread & I hope someone has an answer to my query. I've included a very crude picture of the bearing on my new turntable & wondered if I'm right about running the belts higher up the platter? I don't want to automatically think I know better than the manufacturer so I've asked as there could be a very specific reason they designed the motor housing to run the belts at the bottom. The platter is 70mm thick & weighs 7 kilo's but I still think the belt will pull the platter over & cause more metal to metal contact than if run at the top. Thanks in advance to anyone that can help.
http://www.diyaudio.com/forums/attachment.php?attachmentid=328267&stc=1&d=1360021215
 

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It's unlikely to make any difference with a finely toleranced bearing, though the 'risk' of precession will be lower with the lower placement. A taller motor pod is at great risk of being more affected by a small angular offset from vertical than a shorter motor pod would be.

Chances are, if it's a decent deck from a reputable manufacturer that you need not worry about belt position.
 

Arckivio

Member
2012-12-28 11:09 pm
It's unlikely to make any difference with a finely toleranced bearing, though the 'risk' of precession will be lower with the lower placement. A taller motor pod is at great risk of being more affected by a small angular offset from vertical than a shorter motor pod would be.

Chances are, if it's a decent deck from a reputable manufacturer that you need not worry about belt position.

Now I'm going to show my inexperience & ignorance by asking what precession is? Not a bad quality turntable for the money but definitely not a clearaudio, that's why I'm questioning their choices. It's all I could afford I'm afraid while still giving in to m y girlfriands need for eye candy. There is a very slight amount of play in the bearing which is what made me think the belts would be better at the top. Thanks for the reply Sq
 

Arckivio

Member
2012-12-28 11:09 pm
I'm trying to make the best of a bad lot so one basic test I did do, was to run the belts at the bottom & dial it in to 33 rpm & then run them at the top & noticed I actually had to turn the power down significantly to achieve 33 rpm so it definitely is easier on the motor.
 
run it where motor torque is lowest ad measure with current meter..

you would be surprise how much little "engineering" goes into something as critical as a turntable bearing..
It al has to do with rotational center of mass of the platter with record and all installed and needle drag how the bearing is loaded there will be a sweet spot in any sleeve thrust arrangement
 

Arckivio

Member
2012-12-28 11:09 pm
run it where motor torque is lowest ad measure with current meter..

you would be surprise how much little "engineering" goes into something as critical as a turntable bearing..
It al has to do with rotational center of mass of the platter with record and all installed and needle drag how the bearing is loaded there will be a sweet spot in any sleeve thrust arrangement

It's a DC motor with speed control & although I didn't use a meter, it definitely used less power to run the belts at the top. I had to dial it down, maybe a quarter turn. To give you an idea, it's only a 3 quarter turn of the dial to go from 33.3 to 45 rpm.
 
It's a DC motor with speed control & although I didn't use a meter, it definitely used less power to run the belts at the top. I had to dial it down, maybe a quarter turn. To give you an idea, it's only a 3 quarter turn of the dial to go from 33.3 to 45 rpm.

Is there any kind of feedback to the motor to maintain the correct speed?

jeff
 

BenY

Member
2002-07-04 8:42 pm
ISRAEL
Belt location on the platter cannot influance motor load in any way,unless the diameter of the platter changes from top to bottom. but then speed will change too.
The only issue i see here is centering the force applied by the belt with the center of the bearing so the bearing will be loaded evenly, so wear will be minimal.
 

Arckivio

Member
2012-12-28 11:09 pm
Belt location on the platter cannot influance motor load in any way,unless the diameter of the platter changes from top to bottom. but then speed will change too.
The only issue i see here is centering the force applied by the belt with the center of the bearing so the bearing will be loaded evenly, so wear will be minimal.

Surely it would load the motor more if it's pulling the bottom of the platter but isn't at the top. At the bottom its putting more force metal to metal but isn't at the top I think.
 

Arckivio

Member
2012-12-28 11:09 pm
that is why u measure motor current.. duh.. evenly loaded bearing turns easier less load.
but u need album clamp mat and arm load on unit
position of load does effect the bearing load in a sleeve n thrust bearing as i said before.

I will try it with a meter as even I can do that, but it I think it will measure lower current needed with belts at the top as it seems to need less power on the dial. By the way, good idea. Thanks