most are "conventional" bearing. The biggest advantage is that the bearing well can be fiiled with oil that virtually assures no metallic contact.
I have only seen one inverted bearing, The Gyro. It looks more expensive to build but claims that the bearing point is up at stylus level. Whether this improves sound quality or stability or longevity I don't know. The inverted bearing cannot inherently hold oil in the well. What Michell have done is grind a spiral groove into the shaft with an exit hole at the end to allow oil to circulate from a small well at the bottom up around the spindle across the ball area & down through the spindle ( if I understand the mechanics correctly). This may have an advantage of washing away any debris from the bearing surfaces. Maybe this will be quieter, maybe even live longer??
What are yours like?
I went with inverted on my DIY table, and my thrust ball is just below the top surface of the platter, which is 3.5" high and weighs 29 lbs. . I posted a sketch in my thread "Intro from newbie tt builder". I don't know how scientific my initial thought process was, but I thought about the difference between hanging from an object I was gripping with my hands, and standing (balancing) on a small object. The former is more stable.
I ended up with .001" diametrical clearance between the axial bearings (2) and the shaft, and am using a mediun weight oil. I'm just going to let the oil run through, and I have a plugged hole at the top where I will add more as I need to. I can even use a dip stick to check the oil level at the top. I have been playing records for about 30 hours now, and I get very little oil running out the bottom. I listen with a mechanics stethoscope for bearing noise, and hear nothing.
is your oil feed system like a total loss, feed oil in at the top & it comes out at the bottom, then replenish as needed?
The stethoscope can be copied electronically, set up an M.M. cartridge with the stylus resting on top of the arm bearing. Connect it to preamp &/or amp and measure/listen to the output.
You can put very high gain in here and you do not need phono emphasis. Now you can compare mods before & after. You can also leave the deck stationary and using another source play music/tones through your system & measure the feedback into your deck.
I'm new to this site and was wondering if anyone knows the thread type and size of the michell inverted bearing spindle.
The one for the flat disc that holds the platter on the top of the bearing.