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Rega RB110 tonearm vertical bearings torque specs

Discussion in 'audio' started by vicdiaz, May 14, 2019.

  1. Craig B

    Craig B Re:trophile

    To put this into perspective, in the UK at least, the GR1 turntable, complete with tonearm and factory fitted Elektra MM, initially cost the same as an RB250. No doubt, in order to achieve such, more than just the tonearm had to be to a lower specification, with the absolute minimum of production time per unit also having been factored in.
     
  2. Mr Pig

    Mr Pig ^'- -'^

    That's right. The bearings were locked in place with blue locktite, which was a bit of a fecker actually! I had to heat it to soften it but once reset the arm behaved perfectly. I certainly wouldn't hesitate to buy one if the price is good and you're happy to tweak the bearings.

    I do think it's deliberate for exactly the reason you suggest. Rega didn't want a deck on sale that sounded as good as a 2 which cost less.
     
  3. vicdiaz

    vicdiaz Just another analog freak...

    Thanks Craig!!! Time to find a similar tool!!!
     
  4. Mr Pig

    Mr Pig ^'- -'^

    Not remotely necessary. If you're good with your hands you can set them no problem.
     
    vicdiaz likes this.
  5. Craig B

    Craig B Re:trophile

    Perhaps someone should inform Rega that they've been wasting valuable production time bothering with calibrated tonearm jigs all of these decades.
     
    Last edited: May 18, 2019
  6. Mr Pig

    Mr Pig ^'- -'^

    What's best in a production environment when you're making hundreds of something a day and what you need to make one are very different things.
     
    matt j likes this.
  7. Craig B

    Craig B Re:trophile

    Perhaps we can agree that, if it is a bottom rung (or orphaned) tonearm then careful fettling by hand is good enough, whereas, for a supported design with a factory bearing preload of <=1 micron it is best to send it back to the shop in order to retain/restore its intended bearing performance.

    For reference, a micron (aka micrometre) is 1×10−6m, or one millionth of a metre, one thousandth of a mm (0.001mm), or about 0.000039 inch.

    The chance of stopping at the 1 micron of preload of a top RB tonearm bearing on the first try by hand has to be pretty close to none existent. All the more so, when we take into account that once over, even by a micron, there is no going back without starting over with new parts. IOWs, there exists one shot with which to hit the target.

    Below: Typical RB vertical bearing, a pair of which are preloaded by being clamped together via a central rod, threaded on either end such that adjustable nuts bear down on the inner ring of each bearing, with the 1mm flange of the outer ring bearing upon the arm tube bearing housing (i.e. equal but opposite direction of force). This results in the preload depicted in image C below, with the angle of the axis of bearing travel the one side being exactly opposite to that of the bearing race on the other side. Result, maximum rigidity combined with minimum friction.

    [​IMG]

    Bearing preload illustrated (from National Precision Bearing):

    [​IMG]

    Left image:
    A bearing with no play, or an interference fit has all rolling elements loaded, wears and heats up excessively.
    Center image:
    A bearing with standard play in the free state has low rigidity, and rolling elements can slide or skid instead of rotating.
    Right image:
    A standard bearing with proper preload applied will provide system rigidity, reduced vibration, and optimal bearing life.
     
  8. Mr Pig

    Mr Pig ^'- -'^

    Firstly, who's talking about a top arm? If my RB2000 was wonky I'll be honest, despite being very technically capable, I'd probably be sending to to Rega. Fix an RB110 or 300 myself? No problem.

    But also I don't agree about the disastrous effects of going fractionally over. I've set quite a few tonearm bearings by hand and never found it a huge problem. I'm pretty sure Rega set their better arms by hand, you'd have to check that, and I know Johhnie/Audio Origami sets his arms by hand.

    Setting a tonearm bearing by torque is quick and easy but no way is it better that doing it by feel. If fact it's worse. Why? Because it isn't measuring only one thing.

    A torque wrench is measuring the torque being applied to the fastener. That may sound a stupidly obvious thing to say but on a tonearm bearing, that's not actually what we are trying to measure. The torque wrench cannot tell us the bearing friction or the bearing play, it has no idea what those are. All it is saying is what amount force has been applied to the bolt. The problem being that other factors are in the mix between what the tool is telling us and what we want to know.

    Variations in the threads on the rod and nuts will alter the friction when they get together and result in different amounts of torque, turning force, being required to get the nut to the same place. Variations in the tightness of the bearing on its axle, same thing. There's just two things that can easily result in bearing that are the 'correct' torque but nowhere near optimally set.

    So if you want to put together a lot of arms to a ballpark standard very quickly then yeah, build a torque-jiggy thing but if you want to set them as perfectly as possible? Do it by hand or maybe get NASA to build your parts because those are your only options.
     
    vicdiaz likes this.
  9. Craig B

    Craig B Re:trophile

    You may have gotten the wrong end of the wrench there Colin. The jig measures travel beyond a starting position in fractions to multiples of microns using a dial indicator, not torque. The end result being that a certain extremely minuscule amount of torque (preload) has been applied that cannot be accurately applied using a torque wrench, as practical examples of the latter do not measure accurately down that low. As such, the precise amount of torque applied remains unknown but has been arrived at via a form of reverse engineering involving trial and error tests of adjustment with reference to measured tonearm bearing sensitivity* (aka friction) as feedback between iterations.

    I would imaging that the tonearm R&D folk at Rega could tell you what sensitivity would result for every 10th of a micron above the minimum value that they determined to be optimum for your RB1000, however, that would be giving the game away. Come to think of it, perhaps they named it RB1000 because a micron is one thousand of a mm?

    * Tonearm sensitivity, also erroneously referred to as 'friction', is the minimum load required to set a stationary tonearm into motion i.e. the number of milligrams of additional mass at the headshell end of a balanced arm required to overcome bearing friction. This can be accurately tested for using calibration weights. Some examples, from superb through mediocre:
    • Mission 774 <15mg
    • SME 3009/3012 Series 20mg
    • Grace G-707 <20mg
    • Linn Ittok LV II/Ekos <20mg
    • Jelco (OEM and own brand) 35mg ball races, 25mg knife edge
    • Linn Basik LV-X/Basik Plus/Akito <50mg
    I do apologize if I come across as argumentative, but this is a subject that I have been studying intently for many years.
     
    Last edited: May 18, 2019
  10. Craig B

    Craig B Re:trophile

    On a lighter note, cast your eyes upon a Pro-Ject replacement bearing set.

    [​IMG]

    It is no wonder that they sell a tool with the Ikea-like name of 'Adjust it'.
    [​IMG]

    I like the blurb:
    They neglected to add 'or when the central heating or cooling comes on'!
     
    Last edited: May 18, 2019
  11. Mr Pig

    Mr Pig ^'- -'^

    I've taken a few ProJect turntables apart and fixed/rewired a few arms. The build quality is shocking. There is no way I'd buy a ProJect turntable. One particularly cute discovery was a 'carbon' arm-tube that is actually aluminium with a carbon print wrap on it! What the heck?
     
  12. Dowser

    Dowser Learning to bodge again..

    My view is there are 2 types of arm bearing - user adjustable and non-user adjustable. I’ve always considered Rega as the latter, although a 250 I have has obviously had arm bearings re-locked a little messily, I assume at the same time it was rewired by someone. Bearings feel fine to me with no play or friction - not at 774 levels (best I’ve ever handled), but good none the less.

    For user adjustable, I always do it to minimize play - my LP12 came with a Basik & I was shocked how much play the bearing had, even more shocked how much better it sounded after adjustment to minimize!
     
  13. Mr Pig

    Mr Pig ^'- -'^

    Like I've said, I don't really see why? There is nothing magical going on, it's just basic engineering. Sure, if you couldn't put a nut in a monkey's mouth you should probably leave them alone but for someone who has a bit of mechanical savvy there isn't too much to fear.

    Not often you'll find and old Basik that does not have mullard bearings. Yet people still buy them.
     
  14. Craig B

    Craig B Re:trophile

    Ah yes, the 'hybrid' model. It was supposedly an answer to the criticism levied against pure carbon fibre tonearms exhibiting poor performance wrt high-Q resonance modes in the 1-3kHz range.

    Nice to know that the solution was to produce an aluminium tonearm and shrink wrap it with a carbon fibre pattern that makes it appear to be as 'high tech' as the dearer models that exhibit poorer high-Q resonance performance in the 1-3kHz range.
     
  15. Mr Pig

    Mr Pig ^'- -'^

    It's in keeping with the rest of the production quality. Or lack of it. The arms can literally just fall apart. They are largly held together by wishful thinking.
     

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