One for Pops...

[AngrySailor]

Seeing as it’s Father’s Day and dads old Denon is getting a little tired figured he needed an upgrade...

Found this Rega RP3 and pulled the trigger. Was a trade in at the shop that sold it new. Supposed to be mint mint mint condition and only a few hours use. Apparently the guy traded up to something astronomically expense.

 

[J!m]

Great table!

 

[AngrySailor]

Seems to have positive reviews. Some people not real fond of the elys2 cartridge but he can decide if he wants to change it after listening to it. I imagine it will be fine as both our ears are somewhat shot... It should be a step up from his denon SL-5a TT. I have a denon DL-103 MC cartridge he can try also.

I almost bought another Prisma for him but the original motor was FUBAR. Too bad was nice condition otherwise.

 

[laatsch55]

Could have been a parts unit for yours...

 

[AngrySailor]

Could have been a parts unit for yours...

I asked and got a response about the original motor. He will contact me if the buyer doesn’t want it. It was a nice table with original legs and lid, SME II (I believe) tone arm. Wasn’t a fan of the motor conversion. Price would have been reasonable if original I guess.

 

[J!m]

Plenty of tweaks for the Rega. They are very good stock, but of the sea of tweaks, two have the greatest impact:

1) Michell counterweight

2) Aluminum sub platter (various artists)

And it will need some TLC. Pull the main bearing and wash it out (don’t lose the ball!) and then reassemble with a synthetic gear oil. Avoid Dino oil as it (literally) stinks. I have a good one I’m going to begin selling that I’ve tested in my table for seven years...

A new belt will be needed, even if the table is new and unused. Stock belts take a set and produce impressive wow. I sell a kit, with six different elastomers, for finding the sweet spot. Rega offers a white silicone belt for $30 or so but I offer my complete kit for less (and it includes a high purity silicone belt as well as the five other materials). But, most interesting is that the silicone belt (most expensive) is not the most consistent in one independent test.

I can send you one of the least expensive belts I have, no charge, if you want. Most likely exactly what Rega provides but I haven’t had theirs tested.

Once my oil is ready, my plan is to test the belts myself. I have access to a portable non-contact tachometer. It does not give deviation (w&f) but it is accurate. And I can test static (no load) as well as playing a record, with no outside influence. The initial test was done with no load other than the iPhone running an AP on the spinning platter. I think I can do better.

 

[mlucitt]

The gear oils contain extreme pressure (EP) additives because of the shear forces encountered in helical and hypoid gearsets. EP additives which contain phosphorus/sulfur compounds are corrosive to yellow metals such as the copper and/or brass used in bushings. I used Mobile Spindle Oil like this after I cleaned my bearing:
https://www.ajaxtoolsupply.com/spoilno1gavi.html

Most machine shops have it and will give you a 1/2 oz if you bring in a clean eye dropper glass bottle. I would be curious to see how well it compares to your oil.

 

[AngrySailor]

Cool thanks Jim. The table is coming from the dealer who originally sold it and I am told it has been fully inspected, serviced and set up. Also the tone arm has upgraded wiring and counter balance. The shop apparently sends their new tone arms to a place in the UK who does these mods. Now you’ve got me worried about belts... I should have flipped the belt of my Prisma before I left it to sit stationary for two months...

Depending on the type of non contact tach I’m not sure that will work so well at that low rpm... I know my optical tach for machinery won’t read a TT as it doesn’t like much under a couple hundered rpm. Also you would need a bracket to hold it absolutely stationary as any movement of your have will be read as wow and flutter. What’s wrong with a strobe disk? Probably much more accurate that a single pickup point optical at 33 1/3 rpm? You could make a precision frequency strobe light if you don’t trust the 60hz from the wall...

Pops and I used to work at an oil blending plant. “Anglamal” was the additive package that made EP gear oils stink. Imagine stinky gear oil x a gorillion and that’s how that shit smelled straight. Only a small percentage was added to the final product...

 

[J!m]

Spindle oil is good- but it is not designed for high pressure; more for high speed. It avoids foaming and is best at room temp and above (which is obviously fine). Most synthetic gear oils (with a GL rating) are far too heavy for a low speed bearing. But, that EP or GL rating is important since the entire load of platter etc rests on a single point. The PSI on that tiny area is massive. That’s why the stock steel bearing ball develops a flat spot. The oil can’t work under that pressure. An extreme pressure grease is the right answer but it apples far too much drag on the bearing (ask me how I know)...

I recently used that tach at 60rpm and a bit under, and it worked fine. If I’m not happy with data I’ll find another way. But it has to be non contact. The strobe will tell you you’re “on” but not how far off you are, when you’re off.

And I’m aware of certain bronze alloys being attacked by oils. That’s why I ran this stuff for so long before feeling it was “good”. And owning two land-rovers I’m am intimately familiar with the hypoid stench. I plan to market a cologne to Rover owners: a blend of single malt and hypoid. Still working on a clever name.

 

[AngrySailor]

What about a signal generator timing the strobe? Sync it up and measure your pwm frequency.

 

[J!m]

All I need is a signal generator...

There’s an oscilloscope at work, with the manual, I can play with if I want to...

 

[mlucitt]

But, that EP or GL rating is important since the entire load of platter etc rests on a single point. The PSI on that tiny area is massive.

The Extreme Pressure rating is for shear loads, which the spindle bearing does not have. The entire load of the platter is what? Ten or even twenty pounds? This is not extreme pressure (think heat generation) and not quite as heavy the loaded spindle of a machine tool turning a 1000 pound pump shaft on a row of needle bearings me thinks.
Not to be pedantic but the platter spindle should not contact the ball bearing, it should be floating on an oil film - a film created by the proper viscosity of the oil. The viscosity should not be so thick as to create drag on the spindle, but not so thin that it cannot maintain a film under load.
Your spindle shows almost no wear, which means the oil is doing its job.
The ball is harder than the spindle, so when broken in, there should be a microscopic detent in the center of the spindle. This will help retain the oil film and keep the spindle centered.

 

[J!m]

I think we are in complete agreement from two different angles. Ideal film thickness is 1.5 to 4 mills if I’m remembering correctly. I just went through that for my tonearm main bearing, which is a similar design. The shaft never contacts the walls of the well. But the shaft end is another story:

The pressure of a ten pound platter assembly is actuality extreme on a single point. The area is minuscule- a 3/16” ball so, maybe .010” contact diameter? If so, that’s an area of .00007854 square inch. (Pi r^2)

To find pounds per square inch, we have to resolve this.

10 X
——— = — ———-
.00007854 .00007854

X = 127,323.9545 PSI

20 pounds doubles this. Assuming the math is good.

This is why I fear my polymer bearing wont last. It’ll get crushed and stuck in the well. But it’ll be quiet, since it can tolerate dry running nearly as well as Teflon. Teflon of course is far too soft for this application. Then we add my oil, which I have confirmed compatibility with. Some synthetic lubricants can react with some polymers, so I wanted to be sure. I need to test. And inspect my steel ball. I believe it did have a flat spot when this all started about eight years ago now... if I can accurately measure that diameter/area I’ll know the load on the plastic ball which I can compare to the specs of the polymer.

 

[mlucitt]

I appreciate what you are saying, but this is rapidly turning into Newtonian physics. I agree with your math but not the application of it. To use your example, the PSI of 127,323.9 is equivalent to 63.6 tons pushing down on the 3/16" spindle ball bearing, I believe your turntable stand would collapse under that weight. Of course, the platter weight in nowhere near that because PSI becomes nonsensical when the area size is <.1" square.
The output of your calculation relates to contact point stress and PSI is not an appropriate definition of contact point stress. Hertzian stress (pH) is a much better descriptor for point contact stress and it is usually measured in megapascals (MPa). I used your measurements to arrive at 1591.04 MPa.

Your polymer bearing may be good up to 2000 MPa, I say go for it and let us see what happens.

 

[J!m]

I think the data I had
was fracture strength, which is not compressive yield. Not sure how applicable that data is.

I have five or 10 of the balls already for testing. I also have ceramic and silicon nitride. Though those will be quiet due to their surface finish, I have high hopes for the polymer.

 

[Gepetto]

Buy a vintage Rek O Kut turntable and look at the wear on the end of the shaft that contacts the ball bearing. A cheap way to get some real empirical data.

 

[J!m]

I need another table like another hole in my head.

 

[mlucitt]

Buy a vintage Rek O Kut turntable and look at the wear on the end of the shaft that contacts the ball bearing. A cheap way to get some real empirical data.

Horrible name, great workhorse turntable.

 

[AngrySailor]

The spindle shaft on the Prisma is cupped where it sits on the ball.

 

[Gepetto]

The spindle shaft on the Prisma is cupped where it sits on the ball.

Well there you go. Higher drag, lower PSI. Great taste, less filling