Bodine motor rumble: capacitor? [and more Presto 6N...]

This is where record cutters raise questions about cutting, and trade wisdom and experiment results. We love Scully, Neumann, Presto, & Rek-O-Kut lathes and Wilcox-Gay Recordios (among others). We are excited by the various modern pro and semi-pro systems, too, in production and development. We use strange, extinct disc-based dictation machines. And other stuff, too.

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piaptk
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Bodine motor rumble: capacitor? [and more Presto 6N...]

Post: # 23679Unread post piaptk
Tue Feb 26, 2013 10:07 am

I finally found a place in PDX that fixes small electric motors... when I sent in my old rumbly 6n motor, they called me back and said "this thing runs great, super quiet". And told me that it might be the capacitor it uses is going out. It would make sense, since Kris D and I tried three motors on the same lathe and they were all really loud.

Has anyone ever replaced their Cap? Did it work?
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audadvnc
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Re: Bodine motor rumble: capacitor?

Post: # 23682Unread post audadvnc
Tue Feb 26, 2013 10:38 am

Does the motor mount use rubber shock mounts? It's possible they have aged to the point where they no longer isolate vibration, but carry it on through to the frame.

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piaptk
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Re: Bodine motor rumble: capacitor?

Post: # 23686Unread post piaptk
Tue Feb 26, 2013 11:27 am

We actually replaced those... it's definitely something with the motor.
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ejemmons
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Re: Bodine motor rumble: capacitor?

Post: # 23692Unread post ejemmons
Tue Feb 26, 2013 12:53 pm

Somehow, I really doubt the cap is the problem. Rumble is more likely caused by runout on the motor capstan, hardened/flattened drive pucks, or bad turntable bearing, including flats on the ball bearing at the bottom... Much can be divined from the frequency of the rumble.
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JayDC
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Re: Bodine motor rumble: capacitor?

Post: # 23698Unread post JayDC
Tue Feb 26, 2013 4:57 pm

bad idler wheels, or dirt on the inside of the rim of the platter could give you thuds or a rumble..
generally its for reproduction.. but i like to play wif it sometimes.. :P

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Jesus H Chrysler
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Re: Bodine motor rumble: capacitor?

Post: # 23701Unread post Jesus H Chrysler
Tue Feb 26, 2013 7:43 pm

a bad cap would be more likely to cause it to hum or whine, not rumble.

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Angus McCarthy
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Re: Bodine motor rumble: capacitor?

Post: # 23720Unread post Angus McCarthy
Wed Feb 27, 2013 2:52 pm

ejemmons wrote:Somehow, I really doubt the cap is the problem. Rumble is more likely caused by runout on the motor capstan, hardened/flattened drive pucks, or bad turntable bearing, including flats on the ball bearing at the bottom... Much can be divined from the frequency of the rumble.
I've actually got a similar problem with the motor on my K8. Even without engaging the rim, the motor vibrates so much you can feel it in the platter!

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audadvnc
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Re: Bodine motor rumble: capacitor?

Post: # 23745Unread post audadvnc
Thu Feb 28, 2013 10:15 am

Also, some motor frames (which are made of laminated sheet metal) separate with age and start to hum and vibrate when AC electricity is applied to them.

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Re: Bodine motor rumble: capacitor?

Post: # 23746Unread post Steve E.
Thu Feb 28, 2013 11:15 am

I have found that, post-replacement of the rubber bushings, most of the rumble from my Bodine motor is transmitted through the rubber idler wheels. And yes, these have been Terry-Rubberized.

I think the problem is more significant when playing BACK discs on that platter than in the actual cuts. I have an arm mounted onto the front of my 6N with a short length of wood. Rumble may be transmitting through that wood into the arm.

The rumble can be reduced by reducing the contact point between the motor and the wheel: in other words, by tipping it. I am not saying this is a great idea in the long term, just that it is effective in rumble reduction.

I tried gooping dynamat all over my machine and TT after reading about JayDC's success with it. I hate that stuff. It sticks to your hands and clothing, and I am not sure it reduces the rumble enough to be worth it. Granted, it sounded like Jay did a MUCH more thorough job with it.

Electronic (non-mechanical) hum seems to have a buzzier sound to it.

I bought a cork mat from Vinylike: http://vinylike.de/index.php/store/products/category/usefullstuff/

I have the feeling that might help. We shall see.

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Re: Bodine motor rumble: capacitor?

Post: # 23747Unread post piaptk
Thu Feb 28, 2013 12:05 pm

Dynamat helped a LOT... that is the only thing keeping most of the rumble out of my cuts. The transfer is there (and more noticeable now that I am getting less surface noise), but it's not horrible. Would be nice to get rid of it though!
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markrob
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Re: Bodine motor rumble: capacitor?

Post: # 23748Unread post markrob
Thu Feb 28, 2013 12:20 pm

Hi,

Unless you go to great lenghts, I doubt you'll be able to really kill the mechanical noise. The spec for the 6N states that the mechanical noise is 35-40db below the max useful level that can be cut. I assume here they refer to the 1D head. You would probably have to go to a belt driven setup with the motor well isolated from the lathe to imporve much.

Mark

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piaptk
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Re: Bodine motor rumble: capacitor?

Post: # 23749Unread post piaptk
Thu Feb 28, 2013 2:00 pm

The problem im having is much louder than most 6ns. There is definitely a problem somewhere... Still searching.
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Re: Bodine motor rumble: capacitor?

Post: # 23750Unread post vmspoland
Thu Feb 28, 2013 2:43 pm

The hi , separate all driving drives , but enclose itself engine , then put the plate on the plate , put the insertion with the needle on the plate , you will have a strongly audible voice of the engine , you attend will not do away this , these the boom will be always in such solutions , this engine will be audible even when you will put him on the floor and you will include , the needle put on the plate and thus you will hear the working engine ,
The certain superiority have engines DIRECT DRIVE , because , from May a very small resonance not greater than 2 Hz , and because these engines does not hear wkladka gramophone- , see on the removal, the magnet is directly fast to the plate technics , and the engine is not audible

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Steve E.
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Re: Bodine motor rumble: capacitor?

Post: # 23789Unread post Steve E.
Fri Mar 01, 2013 3:30 pm

piaptk wrote:Dynamat helped a LOT... that is the only thing keeping most of the rumble out of my cuts. The transfer is there (and more noticeable now that I am getting less surface noise), but it's not horrible. Would be nice to get rid of it though!
Where did you put the Dynamat? and where did you NOT put it? maybe I should give that another try.

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Re: Bodine motor rumble: capacitor?

Post: # 23896Unread post Steve E.
Wed Mar 06, 2013 5:13 pm

What is the metal frame resting on? The cabinet, and its position on the floor, are not to be discounted, either.

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Re: Bodine motor rumble: capacitor?

Post: # 23970Unread post Angus McCarthy
Sun Mar 10, 2013 8:55 am

Good point. I've got wood-frame everywhere in the house and it vibrates like nothing else if you hit one of the sweet spots.

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Beware of Dynamat Extreme

Post: # 37604Unread post Steve E.
Mon Sep 28, 2015 9:23 pm

I know I said this earlier in the thread, but....really, really, watch out with Dynamat Extreme. I'm sure it's helpful when used correctly. But, it's also tar-like rubber, or rubber-like tar, with some aluminum on one side. Don't put it anywhere that you might someday, er, not want it. Don't put it anywhere visible or physically accessible. It can only be removed by heating it and melting it off, or by applying dry ice and chiseling it off.

I put it all around the outside rim of the platter of my Presto 6N, many years ago, when I was a newbie. I put it around the base of my monitoring tonearm, too. It shouldn't be there. It looks dumb and I doubt it helps much in those spots. Every time I move the platter, I manage to destroy another shirt.

I'm writing this today because I'm trying to get it off, and it's a horror show.

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Re: Bodine motor rumble: capacitor?

Post: # 45143Unread post Steve E.
Sat Dec 10, 2016 12:33 am

Eventually, naptha turned out to be good for removing Dynamat. You can kinda turn the Dynamat into a tacky, growing ball that will remove itself.

I've been getting my Presto 6N back up and running, as I've gradually settled into my new home after the traumatic couch-surfing period of a couple years ago.

A major order of business has been attempting to reduce platter rumble. Kris D reminded me that I should replace the rubber donuts (grommets) that isolate the motor from the chassis. I remembered that I'd made a bunch of pucks from some good, soft acoustic rubbery stuff a couple years ago --Sorbothane-- and hadn't installed them.

So I did. And I put more pucks under the chassis to isolate it from the cabinet the 6N sits in.

It helped, or at least changed things. It reduced rumble at 60 hz, 120, and 240 hz.

But, I'm still getting a rumble at 30 Hz, and I think it's actually worse than it was. I can't hear it, but it shows up on a frequency analysis. And I can see the rumble as a rapid, vertical change of depth of cut.

I don't think I was getting this before. I used to use a cork mat, and that may have helped. But the cork mat was not utterly uniform in depth, and that created its own serious problems.

Any other thoughts, folks? Is this just a Presto "thing"? It's definitely coming from motor vibrations, almost certainly transmitting through the idler wheel: I turned the motor off and did a brief cut with the platter turning freely -- the depth-changing went away.

Should the dashpot be eliminating this?

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Re: Bodine motor rumble: capacitor?

Post: # 45144Unread post Steve E.
Sat Dec 10, 2016 1:32 am

Also..... I have no rubber under the center flange, connecting the overhead to the spindle. Perrrrhaps that would help?

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Re: Bodine motor rumble: capacitor?

Post: # 45150Unread post Steve E.
Sat Dec 10, 2016 11:35 am

markrob wrote:Hi,

Unless you go to great lengths, I doubt you'll be able to really kill the mechanical noise. The spec for the 6N states that the mechanical noise is 35-40db below the max useful level that can be cut. I assume here they refer to the 1D head. You would probably have to go to a belt driven setup with the motor well isolated from the lathe to imporve much.

Mark
Mark, nice to see this note. This is pretty much what I have going on here, now. It's an inaudible -40 db rumble at 30Hz, with quieter, yet more audible, harmonics at the next 3 octaves (esp audible at 120 Hz). The most concerning thing is that it shows up in the groove as a rapidly changing depth of cut, and I think that just can't be very good.

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