Silicon Nitride vs Ruby bearing for Rega P5

This is very interesting indeed. Let's analyze the facts regarding mass and hardness. Ruby/Sapphire has a density of 3.98G/CM3 whereas Silicon Nitride has a density of 3.44G/CM3, see a very close resemblence here?
On the MOHS scale (hardness) sapphire is 9, second only to diamond, whereas Silicon Nitride is 7.5, slightly softer in comparison. These 2 materials are so similar in density and hardness that IT is hard to believe anyone can discern a difference, especially given the small size bearing we are talking about here (3/16" dia).
I experimented with Silicon Nitride several years ago and since then I've been reading of massive claims of sonic benefit over a ruby or sapphire bearing. If you can hear a difference, brilliant, however I heard no difference at all. This is one of the overblown audiophile observations going, RE. bearings.

"When used to check certain soft materials like Aluminium, Cast Iron, ruby balls tend to accumulate small bits on their surface, rapidly leading to errors in measurements. When used in scanning applications, ruby balls are susceptible to wear, particularly on abrasive surfaces. Silicon Nitride Balls exhibits no tendency to accumulate material and better abrasive resistance. Scanning CMM users report up to 5 times longer tool life with Silicon Nitride Balls than ruby balls." Mr. Tom Breth, Q-Mark CMM Accessories.It seems that actual hardness is not the major issue here but the properties of the materials vis performance over time.

Your quote speaks of a totally different application. A CMM (Coordinate measuring machine) is not a turntable. The probe of a CMM comes in contact with many types of surfaces, some not as smooth as the thrust surface of a turntable. What abrasive surface are we talking about when it comes to a turntable bearing?
Can you add real life experience of your own regarding these bearings in turntable use?

Gents,

I believe we would be correct in assuming that Stefanl cited the CMM application to illustrate the ruggedness of silicon nitride in order to contrast it with the much more fragile ruby material, and he was correct in doing so, if a higher degree of precision over the longterm is our primary concern. Si3N4 would be a material of choice in such case, but ruby would be its sonic equal provided it has no wear, a condition that cannot be certain. In addition to the reasons why it is often selected these days for CMM styli, the Si3N4 ball is also capable of withstanding heat far above what we will ever see in a turntable, but the mere fact that silicon nitride bearings wear better than ruby bearings (which are not ruby at all, but red colored synthetic sapphire) makes it all the more attractive. A piece of grit in your bearing well would most likely spell disaster for a ruby ball, but a silicon nitride one would remain unscathed. Also, Si3N4 has a much better friction coefficient than ruby, and does not tend to develop flats spots when run on hard surfaces, yet given time ruby balls do indeed wear on such surfaces. In fact, it is a commonplace characteristic with them, that factor alone would be an important consideration in a configuration where a captive ball runs on a metal thrust plate. Also, ruby balls in turntables have been known to shatter, regardless of the low speed and heat involved where I nave never heard of such an occurrence with silicon nitrides.

These are all valid reasons, in my opinion, (and the opinions of most who have seriously studied such materials) to opt for Si3N4 over steel or ruby sapphire.

Regards,
Win

Early this morning I swapped out the Ruby Bearing for a Silicone Nitride one in a Planar 3 with the Groovetracer sub-platter and I would not say it is a step backwards.I also use the Ceramic (silicone) Bearing in a Lenco to no detriment to my ears.I agree with Mosin about the Silicone and I only used a Ruby Bearing because I received one with the Groovetracer.So far so good.