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

[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?

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.