Info on the design of Mike's bearing and special oil used
Guys,
Just thought I should post these details Mike has supplied, which I obtained from the thread on Vinyl Engine, as people here can use it for reference purposes:
Quote:
For the Technics SL1200:-- a Completely New Designed Rigid Close Tolerance Bearing...
Design Philosphy:-----
This completely new design of bearing for the SL1200 arose from an evaluation of the shortcomings of the present bearing, and the realization that to extract 100% of the potential sonic quality from the excellent SL1200 Direct Drive Motor then a completely new design of bearing was justified.
This new design based on the considered application of engineering physics, optimizes the allowable design envelope by the use of Computer Aided Design (CAD) and represents the ultimate possible Bearing that can be designed and manufactured to fit within the constraints of the existing SL1200 motor/platter design. This new Bearing has been manufactured to the highest quality possible and I therefore cannot apologize for the price.
It is very interesting to observe how many highly perceptive audio devotees who understand what this bearing will do to their listening pleasure have already ordered one. These are people who seem to have a technical understanding of the merits of the design and who do not demand to have proof of “listening to it”!!! The fact is you are paying for a bearing that you “cannot hear” and consequently what you do hear ‘is all of the recorded music’ faithfully reproduced.
a) The Bearing Housing is machined from a solid billet of machining quality brass bar 65mm dia. by 45mm long.
b) The three locating posts on the Bearing Housing have been made as large as practical (allowing for the manufacturing tolerances of the SL1200) so as to provide the largest possible mechanical contact between the housing and the main chassis and also for maximum accuracy of concentricity with the Magnet Rotor and Motor coil assembly to which it attaches.
c) The centre column of the Bearing, which fits into the centre of the printed circuit/motor coil assembly, has been made as large as possible for maximum rigidity.
d) The bearing bush is made of close sintered bronze impregnated with oil and honed to fit each spindle as a set, to a nominal clearance accuracy of 0.008mm (less than 1/2 of a thousandth of an Inch) There is a procedure to honing sintered bearings A course stone is used on the hone in order to keep the pores of the sintered bearing as open to oil as possible.
e) The main shaft/Spindle is 12.8mm in diameter by 39mm long. The 12.8mm diameter was chosen so as to allow for any under tolerances in the nominal 12.7mm (1/2”) bushes.
f) The main shaft, record spindle and the locating taper are made from a single piece of M200 Cr-Mo tool steel hardened and gas Nitrided.
g) The shaft and Taper are precision ground in a NC grinder to an accuracy of 0.002 TIR. The polished surface finish on Diameter is 0.4 Microns.
h) The vertical load of the Platter and associated copper mat (if fitted) is supported by a 8mm dia. Silicon Nitride Ball. This Ball floats in a 6mm deep cavity cylindrical cavity in the end of the shaft. This cavity allows the Ball to locate within the Honed Bearing for absolute maximum rigidity, removing any possible resonance problems. This design also allows for the maximum length of bearing.
i) The Silicon Nitride Ball rests on a 3mm thick solid carbide pad. These components are housed in a large sealed oil well in the bottom of the bearing housing.
j) The record locating Spindle has been made 3mm longer to cater for those people who wish to use the increasingly accepted copper mats with 200Gm vinyl and center clamps.
k) These Bearings are totally made in Australia by myself with the main spindle being supplied by a high precision tool and gauge manufacturer who is NATA approved and a NCS International-Certified-Quality company for Aero Space and Medical Work.
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SL1200 High Precision Bearing Lubrication....
After some investigative research I have arrived at what I believe to be the ultimate solution for the appropriate oil for the SL1200 HP bearing.
I have selected a very thin Synthetic oil to which has been added very Extreme Pressure additives. I understand this oil is used in Industrial, Aerospace and Military applications where small high speed gearbox are subjected to high torque applications and where thin EP oils are required.
The oil was selected after some collaboration with oil chemists and lubrication consultants one of which, has a masters in Tribology.
I ran my own bearing for 100Hrs after which it seemed to be nicely run in, although this must always be subjective!
I have now run it for well over 1,200 hours at 45rpm with a 1.8Kg copper mat and my own 0.8Kg center weight using this oil. The bearing has been run intermittently in an attempt to simulate real life conditions. On examination of the carbide pad and Silicone Nitride ball under a X70 lens I could not detect any signs of friction. The spindle and ‘Oilite’ sintered bearing insert were unmarked.
All SL1200 HP bearings are shipped with this Synthetic oil. The lower oil chamber is closed after accurately setting the carbide pad distance. The synthetic oil is injected into the chamber via a small hole, to totally fill the chamber. This hole is then plugged and the chamber exterior finish machined. A small syringe of Synthetic oil is supplied with every HP bearing, to fill the oil cavity around the top of the bearing on installation
The Synthetic oil use in these bearings is of the highest grade, and is far superior to the animal or plant based products which were common many years ago in Extreme Pressure ( EP ) applications. This oil contains modern high tech additives, which have only recently been developed by the work of oil Chemists and Physicists and which allow for the use of much thinner low viscosity synthetic base oils to be used. This in turn, reduces viscous drag and loss of power in critical applications such as aerospace.
In an application such as the HP bearing, where the maximum speed is only 45rpm, I believe the oil will last almost indefinitely and certainly perform it’s duties for that period.
I chose a low viscosity oil ISO25/32, so that at the relatively slow speeds encountered, the oil would circulate freely and swirl around the ball and pad, allowing for a constant molecular layer of oil to be drawn into the high pressure point where it matters. Incidentally when you get the syringe full of oil you will notice it is of a light blue colour, this is the EP additives. You may need to top up the oil cavity at the top of the bearing about once every 1-2 years.
Marco.