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What is damping fluid

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What is damping fluid

Postby bmenary » 17 Oct 2012 05:29

Can someone please explain what Damping fluid is and why it's used- I am looking at Graham tonearms and looks like they use this fluid-

As we say in Chicago- TANKS
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Re: What is damping fluid

Postby Coffee Phil » 17 Oct 2012 06:07

Hi Bmentry,

Damping fluid is oil, usually high viscosity, used to provide viscous friction in a tonearm. It will de-Q the resonance formed by the arm mass and stylus compliance. Used properly it will enhance the low frequency response. Some arms such as my Grace 940 (and I think the old Grays) surround the uni-pivot bearing with the oil while others like my SME have as an option an oil filled tray and a paddle attached to the arm and submerged in the oil.

Now-days the oil is typically silicone oil but I'm guessing the Grays used petroleum oil.

Phil


bmenary wrote:Can someone please explain what Damping fluid is and why it's used- I am looking at Graham tonearms and looks like they use this fluid-

As we say in Chicago- TANKS
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Re: What is damping fluid

Postby Bob in STL » 17 Oct 2012 19:48

[quote="Coffee Phil"]Hi Bmentry,

Damping fluid is oil, usually high viscosity, used to provide viscous friction in a tonearm. It will de-Q the resonance formed by the arm mass and stylus compliance. Used properly it will enhance the low frequency response. Some arms such as my Grace 940 (and I think the old Grays) surround the uni-pivot bearing with the oil while others like my SME have as an option an oil filled tray and a paddle attached to the arm and submerged in the oil.

Now-days the oil is typically silicone oil but I'm guessing the Grays used petroleum oil.

Phil

quote]

Phil,

I am consideing fluid dampening for my SME 3009 series II (improved). In your experience does it also improve tracking and therefore allow a wider range of cartridge compatibility? For example, normally you have to add mass to the headshell to use a medium compliance cartridge with a low mass tonearm. If fluid dampening was present does this change or improve anything regarding compliance?
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Re: What is damping fluid

Postby Coffee Phil » 18 Oct 2012 06:03

Hi Bob,

I have an FD 200 but I have not installed it yet. The plan was to install it when the turntable moves upstairs to my stereo room. My Beogram 3000 will replace it in the family room.

There is a complication. I have a Q-up on the Kenwood with the SME. On this turntable the Q-up is where the trough would mount. I do want to use the damper but I've gotten used to the Q-up. I am actually thinking of hooking a motor controlled by a photocell sensor to lift the arm at the end of the record so I can part with the Q-up.

I would expect that with the right damping you could have compliance less than optimum for the arm and get by fine.

Phil
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Re: What is damping fluid

Postby bmenary » 18 Oct 2012 06:09

Thanks CoffePhil-

I think your idea sounds very cool- "a motor controlled by a photocell sensor to lift the arm at the end of the record"
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Re: What is damping fluid

Postby kelvinMunson » 18 Oct 2012 09:54

Several Thorens turntables use an optical sensor to activate the lift mechanism at the end of the record; seems to work well.
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Re: What is damping fluid

Postby johngordon » 18 Oct 2012 11:44

When I was making arms, I used a damping medium called Kilopoise, made by Rocol. It is commonly used in cameras and scientific instruments on screw threads to smooth out the movement.

It was a petroleum based product, and was soluble in lighter fluid, like Ronsonol, or similar. It was available as a high viscosity oil, in light or heavy grades, or as a grease. I used the oil in damping troughs in, for example, unipivot bearings, or for pivoted arms as additional attachments to control vertical movement. As a grease, I used it in cueing devices and on counterweight screw threads.

That grease used silicon dioxide as the filler material, so whether other modern materials are now silicon based or whether they are still petroleum based and the silicon content (silica, ie ultra-fine sand or quartz) is what is being referred to as silicon, I don't know. Personally I don't use silicon based polishes, sprays, or lubricants at all, if I can avoid it, especially near electrical contacts or in locations where where paints or lacquers are used, or are likely to be used.

I have to say, Kilopoise was a brilliant product, though at times incredibly messy....
I have found a data sheet:
http://www.farnell.com/datasheets/494930.pdf

John
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Re: What is damping fluid

Postby cats squirrel » 18 Oct 2012 12:40

I would be very surprised if silica (silicon dioxide) was used in a grease, its a very hard substance, and counter-intuitive to use it in a grease.

Modern greases can be silicones, these are chemical analogues of petroleum based lubricants, but contain silicon atoms rather than carbon, although most contain both!

in summary:
silica: silicon dioxide, as found in quartz
silicon: an element, rarely used alone, except in semiconductors.
silicone: an analogue of carbon based materials, containing silicon atoms instead of carbon atoms.
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Re: What is damping fluid

Postby johngordon » 19 Oct 2012 09:02

Hi Cats,
You said
I would be very surprised if silica (silicon dioxide) was used in a grease, its a very hard substance, and counter-intuitive to use it in a grease.

Well, be surprised, be very surprised... :o


from the data sheet I linked to:
http://www.farnell.com/datasheets/494930.pdf

Thickeners:

0868GW & 0001GW
Micronised polyethylene

0868S
Silica

0868
None (fluid grade)


I presume the silica is held in a suspension such that it plays little part in the dynamics. Given that in these applications there is little movement and such as there is is at low velocities then the hardness of silica isn't a factor. I have cueing devices using 0868S which show no wear after 30 years of use.

And I'd still steer clear of silicons and silicones, especially sprays. They can be a nightmare if you ever have to refinish anything, as they are very difficult to remove.

John
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Re: What is damping fluid

Postby afs97cjh » 19 Oct 2012 11:24

Polymethylsiloxane viscosity standards are sold for calibrating viscosity meters and are similar to the fluid supplied for my Townshend Rock though I can't tell you what viscosity to use.
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Re: What is damping fluid

Postby russellswanborough » 19 Oct 2012 11:32

...I am consideing fluid dampening for my SME 3009 series II (improved). In your experience does it also improve tracking and therefore allow a wider range of cartridge compatibility? For example, normally you have to add mass to the headshell to use a medium compliance cartridge with a low mass tonearm. If fluid dampening was present does this change or improve anything regarding compliance?


I had this very combination some years ago - a SME 3009 II improved - and I purchased the fluid damping kit after using the arm for about 2 or 3 years. The effect on the bass was stunning, much deeper and cleaner. Also, better trackability - I use a variety of cartridges. A notable and very gratifying improvement, well worth the expense.

I hope you have the same results.

Incidentally, I bought the KAB fluid damper kit for my day-to-day Technics SL1200 Mk2 and had similar, but not quite so pronounced, improvements in bass depth and clarity, and some useful trackability improvements - I play some very old LPs (to MP3) for a radio program I host.
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Re: What is damping fluid

Postby JayM481 » 19 Oct 2012 16:42

I'm looking for a UK source of 600000 cst silicone for my Calrad (Grey clone) arm. I know I can get it, eventually, from Turntable Basics, but I'm hoping to find a closer and quicker source, other than industrial where it's available in 200L drums.
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Re: What is damping fluid

Postby cats squirrel » 20 Oct 2012 00:32

Hi John,
thanks for the reference, which does, indeed mention silica as a filler, to increase friction and so aid damping.

I was thinking about grease as a lubricant, rather than use as a damping fluid. But you mention its use on camera and instrument screw threads? Either it's a lubricant, or a damping grease/oil, it can't be both (with a silica filler) surely? :)
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Re: What is damping fluid

Postby Alec124c41 » 20 Oct 2012 03:51

Camera focusing mechanisms and instrument adjustment screws need to turn smoothly, but not freely. Thus the use of damping grease. You can turn things smoothly, then they stay where you want them.

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Re: What is damping fluid

Postby johngordon » 21 Oct 2012 18:40

Cats, you said:
Either it's a lubricant, or a damping grease/oil, it can't be both (with a silica filler) surely?


I believe there are various materials used as fillers or thickeners, among them metals and clays.

A lubricant is just something that makes things slippery. Whether it is a suitable lubricant or not depends on its function - water works a treat for ice skates - not so good for engine bearings... And what works with engine bearings doesn't work with cueing devices. Damping fluids and greases are slippery, just that the rate of slip is low.

It is the viscosity that causes the damping not the fact of being an oil or a grease (or rather a liquid or a semi solid).

John
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