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VPI TNT Bearing question

Trolling the net tonight and ran across a site that showed a MK 5 bearing for the TNT which was attached to the table via a large threaded nut which screwed onto the bearing housing making the housing the equivalent of a giant bolt and nut.

Has anyone done this upgrade? Results? It was suggested that the improvement came from the different attachment method rather than any change in the bearing itself.

Thoughts and experiences?
apbiii
dgarretson
2,609 posts
 
Whatever VPI has done with subsequent iterations of the platter bearing to improve coupling between the bearing housing and the plinth, my point is that massive brass coupling of the metal bearing housing to the platform below will surpass the acrylic plinth in dissipating parasitic vibration from the system. This is based on several modifications to TNT spindle bearing and suspension I've performed that substitute brass for plastic. If you have access to a machine shop, try it you'll see. The construct can be extended to a brass pedestal that extends from the tonearm pedestal through the plinth to the platform. I've done it and it works. After enough of this the acrylic plinth becomes little more than a means of locating the spindle and tonearm in the horizontal plane.
markd51
763 posts
 
On my custom HW-19 acrylic Plinth, the entire MK-IV Bearing Well (with the 3 screw mounting arrangement) is a tight slip fit.

Ny Spindle-Pivot distance on the Plinth is at +- .003".'

Probably the condition of the Bearing, and well itself is more important than what version bearing well.

I could've had a local machinist I know fabricate me a bearing that would've looked like it came of a military 2-1/2 ton truck. With his knowledge, and inspection of my stock MK-IV bearing, and the Platter, his words were "this is fine".

Yes, the 1/2" bearing shaft looks sort of "spindly" IMO.
Reckon the issues at hand are, how much load is on the bearing? There is no heat to speak of. Tolerances, ans smoothness are probably some of the most important factors.

A local machinist who is worth his salt shpuld be able to do anything you want. Tney'll usually charge you a flat rate charge for labor, and then materials acquired-used.
apbiii OP
39 posts
 
Very interesting and thought provoking responses.

I am not worried about aluminum threads stripping and suspect you could shear of the top collar of the bearing housing if you apply enough torque (consider the amount of material engaged in the threads compared to the amount of material in the flange).

Dgarretson has done some very nice mods. As I read more about turntables I had begun to wonder if more mass on the bearing housing would be beneficial and I think he is saying it is.

The feet are pretty slick also. Do I understand that the flex provided by the fingers of the cup which holds the ceramic balls is enough to give a bit of vertical compliance as the four balls on the bottom move in and out allowing the top ball to move up and down? Some more details on the foot construction would be nice.

Your AC supply for the turntable bears some research as I have been looking for something that would do that.

As to machinist, while I am not a pro I do have pretty good skills and a very well equipped shop in my garage so I can fabricate a lot of this sort of stuff.

Lots of food for thought...
brf
1,715 posts
 
I am not a machinist, but I can surely appreciate the precision required to make a bearing that must run true along with providing a 90 degree platform for the platter to rest. How much would a machinist charge for a stainless steel bearing similar to that of the TNT Mark V?
ketchup
700 posts
 
Brf,

It's probably very hard to say. You would first need to know the bearing clearances that VPI is shooting for (it will be a range). For instance, if the bearing clearances are 0.0010", is 0.0015" acceptable or does VPI try to keep it to within 0.0003 instead? Maybe they're going for 0.0002"? The price would change as the tolerances change.

Then there's the surface finishes of the bearing components. Better finishes will cost more money.

The cost of for a bearing with loose tolerances and poor surface finishes will be different than one with tight tolerances and better surface finishes.

If you ask a machinist for advice on what tolerances or surface finishes to shoot for, he may recommend something not even close to the quality that VPI offers as he probably doesn't know how these parameters affect the sound of the turntable. I think it's safe to say that he would not know unless he was a turntable manufacturer.
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