The theory versus the practical reality of oil viscosity in turntable bearings

[Neil McCauley]

I've read a bit and understood quite a bit (but not all) regarding the theory and practice of oil viscosity in turntable bearings. What remains unclear to me, and is the reason for posting this thread is this >

Surely with a high-mass platter (say 4kg or more) any drag characteristics as a consequence of viscosity and boundary-layer effects via any appropriate lubricant would be rendered insignificant by the flywheel effect?

Now having said this I do appreciate that lubricants used in an earth-mover would bring a watch-mechanism to an immediate and irreversible halt and that sewing-machine oil would cause a wind turbine to seize up, and so on. So putting these extreme yet illustrative examples to one side, is the fuss and debate about medium to low viscosity audiophile bearing oil yet another red herring or does it stand up to rigorous and objective mechanical engineering scrutiny?

Thank you
Howard


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[JazzBones]

I've read a bit and understood quite a bit (but not all) regarding the theory and practice of oil viscosity in turntable bearings. What remains unclear to me, and is the reason for posting this thread is this >

Surely with a high-mass platter (say 4kg or more) any drag characteristics as a consequence of viscosity and boundary-layer effects via any appropriate lubricant would be rendered insignificant by the flywheel effect?

Now having said this I do appreciate that lubricants used in an earth-mover would bring a watch-mechanism to an immediate and irreversible halt and that sewing-machine oil would cause a wind turbine to seize up, and so on. So putting these extreme yet illustrative examples to one side, is the fuss and debate about medium to low viscosity audiophile bearing oil yet another red herring or does it stand up to rigorous and objective mechanical engineering scrutiny?

Thank you
Howard


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A subject that is worthy of educated comment is required here Howard, perhaps someone like Mike New, who is well versed on this subject, should give us his experience on this matter, of course allowing for time difference between UK/USA/EU and OZ, over to you Mick :)

Ron

[Clive]

When the Salvation TT was in development I tried thick oil, thin oils, oil mixed with grease and all sorts. In terms of sonics there was little difference between lubes except when they going really thick the bass seemed less agile.

I think the rest of it is down to bearing tolerance with super tight tolerance being best with thin oil. Other than this I think there's too much voodoo in some quarters re oil.

[MCRU]

Others can comment like lubrication experts, me for instance having spent 5 years selling oil and grease, all oils work, it is the ability of the lubricant to conform to the undulations in the metalwork and not be thrown off or drained away, cheap oils will not stick to the surfaces as well as good ones, these light turntable/bearing oils are all basic quality, costing a few pence a litre, better quality oils WILL make the bearing last longer. Prey tell how can the oil used effect the sound?

[Marco]

Castrol GTX give more va-va-VOOM!

Marco.

[DSJR]

The Thorens TD125mk2 (for example) had a bearing, the sleeves of which allowed noticable rock. The original AR legend style deck likewise. Convention has it that the slop in these bearings contributed to a vague and messy sound quality. Thick viscous oil (and even grease in the worst examples) seemed to help here.

Obviously, too tight a tolerance would end up with a bearing with no free movement, but maybe a fairly tight bearing with just the correct grade of oil to add a lubricating film, is best?

[Mike_New]

A subject that is worthy of educated comment is required here Howard, perhaps someone like Mike New, who is well versed on this subject, should give us his experience on this matter, of course allowing for time difference between UK/USA/EU and OZ, over to you Mick :)

Ron

Hi Ron,

I have read a lot concerning folks opinions and ideas on oil and drag on bearings, some just recently when I had cause to challenge the term ‘drag’ when considering my own precision bearings.

In any properly leveled turn table system, it should be realized that at the speed and assuming a generally well balanced platter rotating at 45rpm; there will be very little effective side force and therefore friction on the bearing per se’. In fact, ideally, the only side loading will be the effective loading of the cartridge, (1-2 grams). Which will tend to tilt the platter in the appropriate direction.

Rather the frictional downward force of the spindle onto it’s supporting platform, (of whatever form) will always be the predominant consideration when considering the required properties of a lubricant.

In my own High Precision Bearing I use a vacuum oil impregnated sintered bronze sleeves. (Which I observe others are now using with high fanfare.)
The effective viscosity of the oil in this type of bearing sleeve is predicated on the nature of the sintering and the size of the voids, which take up the oil.
It has little to do with the sonic qualities of the bearing per se’

However in the case of the humble OEM SL1200 bearing, the oil may well have an affect on the sonics of the system as the running gap between the bearing and the shaft is relatively large, ( in fact enormous) The oil acting as a cushion.

However, the oil used in the actual bearing-well where the real downward force of the platter has to be countered, is a very different proposition. In my own bearing I use a very high Extra-High-Pressure (EHP) synthetic oil of much higher viscosity than required by the vertical bronze bearing sleeve. This oil was formulated for me by a local tribologist, who owns a high tech aerospace lubricating oil company.

The actual vertical sintered bronze insert on my bearing is a precision honed bush matched to the individual spindle. Now the oil required for this bush as stated earlier, will be of much less viscosity due to it being required to impregnate the very fine voids in the sintered bronze.
And also to occupy a very much smaller bearing gap, measured in microns literally!!

The primary requirement of any high quality bearing worthy of it’s title, in the audio sonics context, must have absolutely minimum space between it and the accommodated shaft or spindle. Such that no lateral movement of the smallest amount can take place. The oil effectively prevents metal-to-metal contact. And in this respect the sintered bronze sleeve is ideal.

The contact pressure at the base of the bearing can be very high.
In fact if one considers that on a perfect sphere (ball) of an infinitely hard material, any position on this object can be mathematically considered as a singular point.

Now a point in free space, by definition is considered to have zero size, and therefore zero friction (no spatial area) when considered in a bearing!! Therefore it follows that the theoretical pressure at the singular point of contact, between the ball and the bearing pad will be infinite. In fact of course, just like with steel railway wheels a deformation occurs at the point of contact, which in the case of a railway wheel provides the tractive friction for rotational movement on a steel rail.
Now unlike a rolling wheel, our point contact bearing is rotating at the one point in space and therefore requires all the help it can get from an oil that can keep the two materials separated even by a few molecules!!
This is where the relatively new technology of Extreme Pressure Additives comes into their own. Especially in Earth Movers!! as Howard has alluded to. Ball and roller bearings, Epecycloidal gearing you name it!

It also follows that the bearing pad must be of the utmost hardness if it is to meet the requirements of the forgoing. Here, solid, high precision ground carbide meets these requirements as a flat solid surface.

The use of soft Nylon or PTFE, for the pressure pad is in my opinion totally useless, and defeating the requirements of a quality bearing. As the pad will in a short time slowly wear or deform under pressure resulting in increased friction. Also it can, I believe, cause the spindle to bounce vertically.

In conclusion then, oil can only make any real difference in an audio bearing, if it is considered in the context of it’s application. Thin oil for the shaft bearing and good EHP oil for the point of vertical pressure. Depending on the design.

[Neil McCauley]

Hi Ron,

I have read a lot concerning folks opinions and ideas on oil and drag on bearings, some just recently when I had cause to challenge the term ‘drag’ when considering my own precision bearings.

In any properly leveled turn table system, it should be realized that at the speed and assuming a generally well balanced platter rotating at 45rpm; there will be very little effective side force and therefore friction on the bearing per se’. In fact, ideally, the only side loading will be the effective loading of the cartridge, (1-2 grams). Which will tend to tilt the platter in the appropriate direction.

Rather the frictional downward force of the spindle onto it’s supporting platform, (of whatever form) will always be the predominant consideration when considering the required properties of a lubricant.

In my own High Precision Bearing I use a vacuum oil impregnated sintered bronze sleeves. (Which I observe others are now using with high fanfare.)
The effective viscosity of the oil in this type of bearing sleeve is predicated on the nature of the sintering and the size of the voids, which take up the oil.
It has little to do with the sonic qualities of the bearing per se’

However in the case of the humble OEM SL1200 bearing, the oil may well have an affect on the sonics of the system as the running gap between the bearing and the shaft is relatively large, ( in fact enormous) The oil acting as a cushion.

However, the oil used in the actual bearing-well where the real downward force of the platter has to be countered, is a very different proposition. In my own bearing I use a very high Extra-High-Pressure (EHP) synthetic oil of much higher viscosity than required by the vertical bronze bearing sleeve. This oil was formulated for me by a local tribologist, who owns a high tech aerospace lubricating oil company.

The actual vertical sintered bronze insert on my bearing is a precision honed bush matched to the individual spindle. Now the oil required for this bush as stated earlier, will be of much less viscosity due to it being required to impregnate the very fine voids in the sintered bronze.
And also to occupy a very much smaller bearing gap, measured in microns literally!!

The primary requirement of any high quality bearing worthy of it’s title, in the audio sonics context, must have absolutely minimum space between it and the accommodated shaft or spindle. Such that no lateral movement of the smallest amount can take place. The oil effectively prevents metal-to-metal contact. And in this respect the sintered bronze sleeve is ideal.

The contact pressure at the base of the bearing can be very high.
In fact if one considers that on a perfect sphere (ball) of an infinitely hard material, any position on this object can be mathematically considered as a singular point.

Now a point in free space, by definition is considered to have zero size, and therefore zero friction (no spatial area) when considered in a bearing!! Therefore it follows that the theoretical pressure at the singular point of contact, between the ball and the bearing pad will be infinite. In fact of course, just like with steel railway wheels a deformation occurs at the point of contact, which in the case of a railway wheel provides the tractive friction for rotational movement on a steel rail.
Now unlike a rolling wheel, our point contact bearing is rotating at the one point in space and therefore requires all the help it can get from an oil that can keep the two materials separated even by a few molecules!!
This is where the relatively new technology of Extreme Pressure Additives comes into their own. Especially in Earth Movers!! as Howard has alluded to. Ball and roller bearings, Epecycloidal gearing you name it!

It also follows that the bearing pad must be of the utmost hardness if it is to meet the requirements of the forgoing. Here, solid, high precision ground carbide meets these requirements as a flat solid surface.

The use of soft Nylon or PTFE, for the pressure pad is in my opinion totally useless, and defeating the requirements of a quality bearing. As the pad will in a short time slowly wear or deform under pressure resulting in increased friction. Also it can, I believe, cause the spindle to bounce vertically.

In conclusion then, oil can only make any real difference in an audio bearing, if it is considered in the context of it’s application. Thin oil for the shaft bearing and good EHP oil for the point of vertical pressure. Depending on the design.

I found your reply VERY interesting. Thank you. Sincerely, Howard.


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[sq225917]

Where would the impetus come from to cause the spindle to bounce? Surely a softer plastic thrust plate would be no different to a metal point in causing vertical bounce.

Sintered bearings are designed/created for use in high rpm conditions where no additional lubrication can be added. As the shaft rotates the bearing heats up due to friction which releases oil from the pores of the of the sintered material. I've not seen the specification for a new sintered material that works specifically at low temp and low speeds. Has some manufacturer developed a new material specifically for sub 100rpm and sub 50 degree operation? Otherwise it's just another metal on metal bearing surface and then suitability comes down to tolerance and surface finish, surely.

[Mike_New]

Hi Simon,
I cannot agree with your observation that sintered bearings are created for high RPM, they are used extensively in all shafting applications including gear boxes. I even had a washing machine that was fitted with them.
I was not making any claim for any special material, in fact the sintered sleeves I use are a standard product.

You are correct about tolerance and surface finish.
The secret is knowing how to hone them for a micron fit to the shaft also they are re-oiled after honing.

[JazzBones]

Hi Ron,



The use of soft Nylon or PTFE, for the pressure pad is in my opinion totally useless, and defeating the requirements of a quality bearing. As the pad will in a short time slowly wear or deform under pressure resulting in increased friction. Also it can, I believe, cause the spindle to bounce vertically.

In conclusion then, oil can only make any real difference in an audio bearing, if it is considered in the context of it’s application. Thin oil for the shaft bearing and good EHP oil for the point of vertical pressure. Depending on the design.

G'day Mike,

I believe that the surface of a PTFE pad can scar and scratch being a soft material, at least from my observations of the surface of artificial skating rinks, and long term use, assuming the PTFE pad hasn't totally mushed up, will do no favours to any bearing. Try an imagine the PSI force of the bearing upon pad or if you want the pain factor, a heafty weight woman (or man...gotta be careful here :)) in a stiletto heal shoe standing on you foot, I would want an armour plated boot and not a PTFE toe cap to protect my delicate tootsies? :eyebrows:

Ron

[shane]

I'm probably missing the point here, but if you have a thin oil for the sleeve bearing and an extreme HP oil for the point contact, how do you stop them mixing together?

[sq225917]

Hi Simon,
I cannot agree with your observation that sintered bearings are created for high RPM, they are used extensively in all shafting applications including gear boxes. I even had a washing machine that was fitted with them.
I was not making any claim for any special material, in fact the sintered sleeves I use are a standard product.

You are correct about tolerance and surface finish.
The secret is knowing how to hone them for a micron fit to the shaft also they are re-oiled after honing.

Mike, I wasn't implying you were making magic claims, you seem far to straight up and down for that. If you read the supplied specs from any decent supplier of Oilite style bearings they will quote expected loads and spindle rotation speeds for the bearings. They were designed originally for adverse conditions, high load, high rpm and minimal service interval.

That they still find there way into other products in this day and age says reams about the education of designers and the practices associated with designing down to price instead of up to spec. They offer no benefits over other metal journal bearing designs when used in turntables. As you rightly state it all comes down to finish, and yours look superbly made.

[Mike_New]

The big advantage of using a sintered sleeve in an audio appication, is that because the oil is held within the bearing metal a much closer honing clearance and tollerance can be held. The real secret, I am told by my toolmakers is knowing how to hone a sintered sleeve so as not to close over the pores in which the oil is held. I was fortunate enough to locate a group who had been doing this sort of work in aerospace applications.

[colinB]

Im curious Mike. Why did you choose to house the bearing in brass as opposed to say steel. Ive been trying to track down the WHF mag that has the letter you wrote explaining the priciples behind it but i cant seem to get a hold of it.

[Mike_New]

Hi Collin,
Steel could have been used, except that the co-efficient of thermal expansion of the brass housing and the sintered sleeve are comparable, when one has to consider the extremely fine clearances that the bearing is honed to. I could also have used bronze.
However Brass is a lot more expensive that steel, this is one of the reasons why my bearing is a bit expensive.
Brass also looks aesthetically pleasing.

[colinB]

The brass does look great but its the spindle i cant top looking at. It makes the original look like an after thought.