Reducing noise from cabinet mounted motors

In the interest of keeping the neighbours sweet I am wondering how best to reduce the humming noise from my mill and lathe, both of which
have cabinet mounted single-phase motors. Both have the motor bolted to large steel plates with a pivot at one end which is in turn bolted to the stand. I have another lathe with external single phase motor and that is fairly quiet.
I am assuming that most of the noise is through mechanical transmission to the sides of the cabinet which act like speakers, so I was thinking of rubber mounting the motor on the plate or maybe using metalastic bushes in the pivot point - and some other sort of isolation for the adjuster on the other side of the plate.
Alternatively (or in addition) I could try and damp the movement of the panels.
If anyone has been down this road and has some advice, then I would be interested to hear.
Thanks Steve
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On Fri, 2 May 2008 02:04:42 -0700 (PDT), Cheshire Steve

    Steve....as well as trying to reduce the generation of sound at source, also give some thought to preventing the sound you *do* produce from actually escaping from your shed/garage/workshop.......simple things like reducing unnecessary air gaps through which sound can travel, installing sound-absorbing surfaces wherever possible....three quarter inch 'softboard' on the walls and ceiling is cheap and very useful for this purpose. It also helps to retain heat and prevent rust etc.
    I just cranked sound proofing into Google and got 1,720,000 hits including this: http://www.diydoctor.org.uk/projects/sound_proofing_in_the_home.htm which should tell you all you need to know.
--
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

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On Fri, 2 May 2008 02:04:42 -0700 (PDT), Cheshire Steve

Steve, I would say you are on the right track. There are basically three approaches 1) don't generate the noise(vibration) 2)Isolate the vibration 3)damp the vibration where it's a problem.
You can't really attack item 1 other than making sure the motor & pulley are (reasonably) well balanced there will always be some residual vibration so...... It is most likely that the 'tin-work' is vibrating at its natural/resonant frequency so isolation of the motor will help and is a good thing to do, but it will have to be very good to really get a major result.
You are probably likely to get better, quicker results by damping or stiffening (ie changing the resonant frequency) of the cabinet panels. The sort of stuff they use for sound absorbtion in car footwells might be a possibility - some of it is sound-deadening rather than absorbtion. It's heavy, well damped and sticky-backed. That will tend to lower the resonant freq. Sorry I don't know where to buy it, but try a body shop.
The other alternative is to raise the resonant frequency by stiffening the cabinet panels - say screw some light angle iron across the diagonals of the offending panels. Possibly glue it on with silicone so that it is 'attached' over all its length. The result would be similar to having a cruciform pressed into the panel (as in car boot floors etc for just this reason).
Lastly as already noted, bung up holes in the walls/eaves and generally do what you can to stop noise getting out of the workshop.
Richard
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On 2 May, 11:36, Richard <sharkface-pilot at toucansurf dot com> wrote:

Thanks,
I had thought about reinforcing the panels, but hadn't though about using silicon so you don't get noise between the panel reinforcing and the panel.
I suppose any empty hole will have one or more natural frequencies, so I had wondered if I would be better using a 3-phase motor and inverter and tuning the inverter to a quiet frequency. I have an inverter and an old motor to try it (think they are both about 1 hp), but it will no doubt be quite a job. Maybe it will be enough just to clamp the motor inside and try it without worrying about the drive system.
Is a three phase motor quieter anyway, regardless of frequency ?
Steve
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On Fri, 2 May 2008 04:07:04 -0700 (PDT), Cheshire Steve

Three phase motors produce a constant torque, whereas single phase motors produce a torque that varies at twice the line frequency. This causes a lot of the vibration with single phase motors/cabinets.
I made a very noticeable difference to my Myford cabinet by feeling which panels were resonating and then gluing lead flashing to the panels with impact adhesive. It adds mass to the panels and also adds damping. It did help that I'd got a couple of yards of 300mm wide flashing left over from when I did the workshop roof :-)
Mark Rand
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