VPI TNT Bearing question

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?

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.

Thanks Ketchup. You have confirmed my suspicion that it sounds easier than it is…… plus you are taking a gamble that it will work and sound good. If I had machining skills and access to equipment, it would be a fun project to attempt with the only real cost being materials. I see a lot of threads on DIY plinths, outboard tone arm mounts, motor drives etc, but very few are attempting their own bearing and platter assembly (except for Dgarretson)

Yes it is a bit of a crap shoot but you really would not have much invested except time unless you use some super exotic bearing material such as rulon and even then you don't need much of it for a TT bearing.

I think making a turntable bearing for a one off is a bit easier than manufacturing them. On a one off you only need to get the clearance right, the absolute dimensions don't matter that much.

You would need a decent lathe with a tool post grinder and someway to ream or hone the bearing to fit.

I have not seen anyone attempting this task. As I understand it Dgarretson only made a weight to attach to his bearing, not the complete bearing.

I'm not sure what sort of clearance is involved but I have two VPI bearing / spindle sets and they are both pretty tight.

I took a staged approach developing the corner towers, evolving from sorbethane of the original TNT Jr., to springs, to a rigid mass-loaded approach using solid hardwood and later brass in feet, and finally to brass with a DIY Stillpoints-style core. There are a few others who have adapted Stillpoints or rollerballs to the TNT. With a chrome spring-steel hole plug from Lowes and 1/4" and 3/8" ceramic ball bearings from Boca Bearing, it is possible to emulate the Stillpoints idea inside the VPI stock elephant feet, which further benefit from being recored in brass. To solidify and better couple the now unsuspended plinth, I eliminated the threaded leveling mechanism from the suspension tower and substituted a leveling mechanism underneath the platform supporting the TT. With this last step the TNT and its platform perform as a system.

It requires a lathe to make a spindle bearing. There are several plastic materials harder and less compressible than delrin for thrust plates, and ceramic balls that sound better than steel for various reasons. AFAIK, I am unique in encasing a floating ball in a donut between dual thrust plates. I considered updating to the inverted bearing, but rejected this for the reasons stated above. Having owned and discarded the TNT 3-pulley system, I was curious to find a better way to center the spindle bearing that would also support thread drive. Theoretically the centering mechanism should lessen somewhat the need for closer clearance tolerances between the spindle and its cylinder. In fact, once the drive system finishes torquing through start-up, there may be reduced friction/noise with a bit more clearance. IMO the unfocused sluggish sound of soft rubber belts is the Achilles heel of all VPI designs. The idler wheel that I added centers the platter and provides better traction for the thread. Thread drive is the best thing that can be done to realize the potential of these TTs.

Mark Kelly's AC-1 sychronous drive controller kit has been out of production for several years. I believe he does similar work for OEMs and perhaps custom jobs. I've never compared it directly to an SDS or Walker controller, but the AC-1 killed the PLC in my system. The fact that the AC-1 is a two-phase controller has advantages. The SDS is a single-phase controller that works with a phasing capacitor.

The TNT offers simplicity and lots of space to work through DIY mods, which is the main reason I've stayed with it since the mid 90's.