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 Post subject: Idler Wheel Question
PostPosted: Feb Fri 18, 2011 5:03 am 
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Joined: Sep Tue 22, 2009 12:34 am
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Hi. I'm working on a suitcase record player with a rubber idler wheel drive. The original wheel was as hard as a rock, so I found another wheel with good rubber on it that was (surprisingly) easily removable. I chucked the wheel on a drill and used sandpaper to bring the new wheel down to the diameter of the old wheel, removed the rubber, and glued it in place on the old wheel.

As it is now, the turntable turns at a steady pace, but the speed is just a couple of RPMs too slow. I'm wondering how the "gearing" is set up on a turntable like this. I can see by the stepped spindle from the motor that the speed increases as the spindle's size increases, but how about the rubber wheel? If I sand more of the diameter away, how does this affect the speed? I'm sanding small amounts, and it doesn't seem to be doing much either way. Any help is appreciated. Thanks! -Shane


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 Post subject:
PostPosted: Feb Fri 18, 2011 5:06 am 
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Location: Woodinville, WA 98072
You probably took it down a just a tad smaller than the correct diameter.


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 Post subject:
PostPosted: Feb Fri 18, 2011 5:37 am 
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Location: Little Rock, Arkansas
Email Gary at VM with your phonograph model # to see if he has a new idler for it. The new one shouldn't run but about $25. This is what it will take to fix it.

http://www.thevoiceofmusic.com


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 Post subject:
PostPosted: Feb Fri 18, 2011 5:44 am 
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Location: Woodinville, WA 98072
Shane,
I recently purchased an idler wheel from Gary for my RCA 9Y510 player. He is very nice, great to work with, and sent the idler wheel very fast.

Steve


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 Post subject:
PostPosted: Feb Fri 18, 2011 6:00 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Boston, MA USA
Unless it is an RCA Victor 45 player with a two-level idler wheel, the diameter of the wheel will change the speed of the turntable not at all. The speed is determined by the ratio of the motor spindle to the turntable inside diameter. The idler has nothing to do with it.

-David


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 Post subject:
PostPosted: Feb Fri 18, 2011 7:02 am 
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dberman51 wrote:
Unless it is an RCA Victor 45 player with a two-level idler wheel, the diameter of the wheel will change the speed of the turntable not at all. The speed is determined by the ratio of the motor spindle to the turntable inside diameter. The idler has nothing to do with it.

-David
^^^ This.... 8)


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 Post subject:
PostPosted: Feb Fri 18, 2011 8:03 am 
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Location: Little Rock, Arkansas
dberman51 wrote:
Unless it is an RCA Victor 45 player with a two-level idler wheel, the diameter of the wheel will change the speed of the turntable not at all. The speed is determined by the ratio of the motor spindle to the turntable inside diameter. The idler has nothing to do with it.

-David


In theory, that may be true. But in actuality, sometimes it isn't true. I've worked on several RCA RP-205 changers in the last year that were running slow on either 33 or 45rpm. In all those cases, I subbed brand new turrets from some of my personal players, and the new turrets made no difference. However, when I installed a new idler on them, every one of them came right up to perfect speed. So I know from experience that a worn idler can affect speed somewhat.


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 Post subject:
PostPosted: Feb Fri 18, 2011 1:56 pm 
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moses_007 wrote:
dberman51 wrote:
Unless it is an RCA Victor 45 player with a two-level idler wheel, the diameter of the wheel will change the speed of the turntable not at all. The speed is determined by the ratio of the motor spindle to the turntable inside diameter. The idler has nothing to do with it.

-David


In theory, that may be true. But in actuality, sometimes it isn't true. I've worked on several RCA RP-205 changers in the last year that were running slow on either 33 or 45rpm. In all those cases, I subbed brand new turrets from some of my personal players, and the new turrets made no difference. However, when I installed a new idler on them, every one of them came right up to perfect speed. So I know from experience that a worn idler can affect speed somewhat.


No Larry, sorry.
The idler tire doesn't determine the rotational speed of the turntable.
We've discussed this before.

It's about surface physics, friction, and slippage... not surface diameter.

a 2 inch wheel will spin half as fast as a 1 inch wheel, if driven from the same motor shaft at a given RPM...... however it will still drive a 10 inch wheel at the same RPM speed as the 1 inch did.

When you subbed, the already warmed-up motor was on speed, making you think there was a change.

The discussion of motors running slow when cold is a clue.

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 Post subject:
PostPosted: Feb Fri 18, 2011 4:32 pm 
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dberman51 wrote:
Unless it is an RCA Victor 45 player with a two-level idler wheel, the diameter of the wheel will change the speed of the turntable not at all. The speed is determined by the ratio of the motor spindle to the turntable inside diameter. The idler has nothing to do with it.

-David

You're 99% right :wink: VM did make some multi-speed turntables with 2-tier idlers. These VM changers were produced chronologically in-between the tri-o-matic three-turret models, and the multi-speed Single-Tier-Idler models. In the 2-tier-idler models, the idler stayed in the same vertical position on all speeds; the ENTIRE MOTOR was raised and lowered by the speed control knob. When you changed speed, you could see the whole turntable chassis bounce a little, due to the massive motor moving up or down. I'd guess these VM's to be from around 1955.

Shane, here is a pic from the VM Voice Of Music website, of some idlers & turrets: Does yours look like the left idler (single-tier) or the right idler (two-tier)?: (actually, I think the 2-tier idler pictured here may be from VM's 45 model, but I've got a VM changer with a similar-looking 2-tier multi-speed idler):

Image

Most likely, your idler is single-tier, like the one on the left - if so, then as RT & dberman51 said, it's just a matter of good smooth properly-toleranced-and-oiled bearings & physics - diameter doesn't matter, as long as the outer edge of the rubber is still circular and not oblong (which would be immediately noticeable as a fluttering / uneven speed, but you don't seem to have that problem): But, as Larry also said, a fresh idler will often bring you up to speed, if the original idler had worn / dirty / damaged bearing surface, or any loss of grip at all (assuming your motor is warmed up).

- Bob


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 Post subject:
PostPosted: Feb Fri 18, 2011 7:09 pm 
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Joined: Sep Tue 22, 2009 12:34 am
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Thanks for all the replies, and the link to the VM site (which I previously didn't know about!).

My wheel looks like the one on the left. I'm going to see if there are any issues with the wheel gripping the parts it needs to grip.


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 Post subject:
PostPosted: Feb Fri 18, 2011 7:36 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Boston, MA USA
moses_007 wrote:
dberman51 wrote:
Unless it is an RCA Victor 45 player with a two-level idler wheel, the diameter of the wheel will change the speed of the turntable not at all. The speed is determined by the ratio of the motor spindle to the turntable inside diameter. The idler has nothing to do with it.

-David


In theory, that may be true. But in actuality, sometimes it isn't true. I've worked on several RCA RP-205 changers in the last year that were running slow on either 33 or 45rpm. In all those cases, I subbed brand new turrets from some of my personal players, and the new turrets made no difference. However, when I installed a new idler on them, every one of them came right up to perfect speed. So I know from experience that a worn idler can affect speed somewhat.


Larry, please read the original posting. We are not talking about a worn idler wheel. We are talking about an idler wheel with good rubber which has been ground down. As long as it grips properly it will have no effect on speed. Of course, if it is not gripping properly because it is too small to reach the turntable or it is in poor condition, all bets are off.

-David


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 Post subject:
PostPosted: Feb Fri 18, 2011 7:57 pm 
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Location: Little Rock, Arkansas
Okay, I guess we are talking about two different things here. I do know that an older idler wheel that through the years has lost some of its rubber can and will affect speed. I just finished an RCA 7-HF-5 that was exactly this way. Even with a new turret installed, the speed was somewhat slow at 33rpm. Once I received the new idler from Gary at VM and installed it, it was right on speed.

Occasionally, even with a new turret and new idler, the speed might be a tad slow. In this case, a close examination of the idler and turrets may reveal that the idler isn't making proper contact with one or more of the turrets. This issue can be corrected by slightly shortening the idler spring.


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 Post subject:
PostPosted: Feb Sat 19, 2011 3:43 pm 
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Location: South Western Ontario Canada
The size of the idler will not affect the turn table speed in the number of feet/minute that the idler travels on the tuntable but it does affect it by the amount torque required by the motor to drive the turntable. Thus affecting the speed. To understand this take a look at a relatively modern turntable with pitch adjustment. There is only one idler on mine but I can vary the speed using the pitch adjustment which just repositions the idler wheel slightly. I even have an old turntable which has a sticker under the platter telling what size idler to use based on mains voltage. Another way to look at it is, what would turn the platter more easily, a large idler wheel or a small one? Obviously, it would be the small one. So I think if you took a little more off of the idler wheel, you would get to the correct speed.
Bob


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 Post subject:
PostPosted: Feb Sat 19, 2011 4:21 pm 
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Bob Masse wrote:
The size of the idler will not affect the turn table speed in the number of feet/minute that the idler travels on the tuntable but it does affect it by the amount torque required by the motor to drive the turntable. Thus affecting the speed. To understand this take a look at a relatively modern turntable with pitch adjustment. There is only one idler on mine but I can vary the speed using the pitch adjustment which just repositions the idler wheel slightly. I even have an old turntable which has a sticker under the platter telling what size idler to use based on mains voltage. Another way to look at it is, what would turn the platter more easily, a large idler wheel or a small one? Obviously, it would be the small one. So I think if you took a little more off of the idler wheel, you would get to the correct speed.
Bob


Another fallacy.

I can see the people insisting on the fact that idlers control speed..... never took up physics and somehow believe that "diameter" of said wheel is the clue..... it's not.

THE---MOTOR----SHAFT---DIAMETER---DETERMINES---THE ---SPEED.

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 Post subject:
PostPosted: Feb Sat 19, 2011 7:03 pm 
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Bob Masse wrote:
The size of the idler will not affect the turn table speed in the number of feet/minute that the idler travels on the tuntable but it does affect it by the amount torque required by the motor to drive the turntable. Thus affecting the speed. To understand this take a look at a relatively modern turntable with pitch adjustment. There is only one idler on mine but I can vary the speed using the pitch adjustment which just repositions the idler wheel slightly.

Wrong again.

The pitch adjustment you are describing works because the motor spindle is slightly conical, so by varying the vertical position of the idler you are causing it to contact varying diameters of the motor spindle, thus affecting the speed. This is how pitch adjustment on Dual turntables is performed.

Again, if a single-level idler is in good condition and therefore able to transmit the proper torque to the turntable, its diameter does not affect the turntable rotational speed. Laws of physics, guys.

-David


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 Post subject:
PostPosted: Feb Sat 19, 2011 7:15 pm 
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dberman51 wrote:
Bob Masse wrote:
The size of the idler will not affect the turn table speed in the number of feet/minute that the idler travels on the tuntable but it does affect it by the amount torque required by the motor to drive the turntable. Thus affecting the speed. To understand this take a look at a relatively modern turntable with pitch adjustment. There is only one idler on mine but I can vary the speed using the pitch adjustment which just repositions the idler wheel slightly.

Wrong again.

The pitch adjustment you are describing works because the motor spindle is slightly conical, so by varying the vertical position of the idler you are causing it to contact varying diameters of the motor spindle, thus affecting the speed. This is how pitch adjustment on Dual turntables is performed.

Again, if a single-level idler is in good condition and therefore able to transmit the proper torque to the turntable, its diameter does not affect the turntable rotational speed. Laws of physics, guys.

-David


That's what I've been sayin'. Dave! :shock:

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 Post subject:
PostPosted: Feb Sat 19, 2011 7:20 pm 
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If the idler wheel is in good condition and is not slipping it still comes down to the load being placed on the motor that is causing the problem.


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 Post subject:
PostPosted: Feb Sat 19, 2011 7:38 pm 
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RepairTech wrote:
That's what I've been sayin'. Dave! :shock:

I know you have been saying it. It's correct, so I'm helping you say it with a little more explanation about the variable pitch control. Some folks are not yet convince so we may have to say it a few more times yet.

-David


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 Post subject:
PostPosted: Feb Sat 19, 2011 7:45 pm 
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Bob Masse wrote:
If the idler wheel is in good condition and is not slipping it still comes down to the load being placed on the motor that is causing the problem.

And if the idler wheel has anything to do with the load on the motor there is a much bigger problem. It is important that the idler's bushing be kept clean and lightly lubricated or else it will drag and either slip on the motor shaft or slow down the motor. It goes without saying that the turntable mechanism must be kept in good condition for accurate speed.

-David


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 Post subject:
PostPosted: Feb Sun 20, 2011 1:43 am 
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If spun by hand, (finger?) the idler should continue to spin for a second or two..
Same goes for the motor shaft.
The turntable platter should spin for at least 10 seconds, (out of cycle) or more.

And there folks, ya have it. :wink:

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