Unscrewing the waaay too tight cap on a Rega fingerlift

Discussion in 'Audio Hardware' started by Board, Aug 7, 2021.

  1. Board

    Board Forum Resident Thread Starter

    Soooo ... now the local RC shop finally got some silicone oil back in stock. I bought the 500,000 cst one, which cost me €5.
    I timed the descent, and if do a small trick of positioning the lever so that when I let it go it slowly tips and starts dropping down on its own, the descent takes just under 9 seconds. If I just push the lever all the way down the descent takes just over 5 seconds. My previous tonearm was a bit easier: Just push the lever all the way down and walk away, and it would very slowly drop down. No tricks needed.
    If these 9 seconds are not slow enough for me in the future, I will go back to the shop and buy either 1 million cst or 2 million cst, because they had that too.

    As for why I used grease and not silicone oil to begin with, I had read a bit on various forums, and while I might misremember this, then I was under the impression that using grease was either preferable to or at least as good as using silicone oil, and that using lithium grease was just as fine as silicone oil as long as it had the same viscosity.
    Although I was obviously mistaken about this, I actually thought grease might have been thicker than the silicone oil, and therefore using the lithium grease I bought would have made for a slower descent.
    I found the conversion from cst to the grease thickness scale difficult to figure out, but I was under the impression that the grease thickness I had found corresponded to something like 200,000 to 300,000 cst.
    In any case, I think the issue is fixed now, and if not I can buy the 1 or 2 million cst in the local shop.
    So, I thank you all for your help. Obviously, using the silicone oil was the right move, and I'm still a bit shocked that buying that tool for the metal cap made such a difference.
     
    Ripblade and Davey like this.
  2. Agitater

    Agitater Forum Resident

    Location:
    Toronto
    What you’re missing is that lithium grease and silicone oil have different flow rates, different reaction to compression, and one doesn’t flow at all in any way under the sort of tiny compression and small spaces found in a tonearm lift. Silicone oil, on the other hand, flows into every nook and cranny (rather that sticking in place like lithium grease - which is therefore useless for your purpose), responds by reflowing exactly as needed (which lithium grease can’t do because there is no heat or pressure in a lift mechanism sufficient to even come vaguely close to making it do so), and silicone oil because of its flow characteristics tends to equalize pressure in all areas of an enclosed hydraulic space like a tonearm lift (something which, again, lithium grease can’t do).

    When you attempt to compare silicone oil with lithium grease in this application, you’re comparing lubricants with dramatically different characteristics - apples and oranges, essentially.

    With the makeshift tool you used, you may have thought you were exerting rotational force on the cap. It is most likely that you were exerting more downward force to keep the makeshift tool in place than rotational force. Basically, excess downward force defeats the effort. What the correct tool did was to help you exert most of the force rotationally, and that’s why it worked so well. Those are the mechanics/physics of this sort of thing.
     
  3. Boltman92124

    Boltman92124 Fish tacos.

    Location:
    San Diego
    AKA-Chuck G likes this.
  4. Board

    Board Forum Resident Thread Starter

    So just out of curiosity: If I had used an even thicker grease, for instance one that was close to being as solid as soap, it would still not have worked in a tonearm lift?
    I still seem to remember reading that someone had used grease, but maybe they had actually used oil and then mistakenly written "grease" because they were greasing the components (with oil). But anyway, that doesn't matter now, and maybe I remember it incorrectly :).
     
  5. Agitater

    Agitater Forum Resident

    Location:
    Toronto
    Correct. In this configuration of tiny pressure and very small clearances available for lubricant flow, lithium grease cannot act hydraulically. It can only lubricate poorly because it cannot fill the interior spaces in the lift mechanism, it cannot flow, and therefore cannot do anything but only slightly damp movement. Plus, because lithium grease is non-hydraulic in these circumstances, an even thicker version could have stopped all unassisted lift mechanism movement entirely. Grease is the wrong lubricant for the application.

    Somebody misstating something in a forum post somewhere? Impossible! :laugh:
     
  6. Board

    Board Forum Resident Thread Starter

    True! I could not possibly happen :cool:.
    Anyway, thanks for your explanation. It makes sense and it's nice to know.
     
    Agitater likes this.
  7. Board

    Board Forum Resident Thread Starter

    This is just a quick update meant as a help in case anyone stumbles across this thread in the future, so the people who have participated don't need to respond to this.

    When I put it in the 500,000 cst silicone oil I put in plenty, so eventually some of it got pushed out, and the descend time went down to 2-3 seconds again.
    So I bought the 2 million cst oil and put that in instead, after cleaning out the thinner oil, and I'm happy with the descend time now.
    The descend time is usually much slower the first time in a day that I use the lift, and one time I measured the descend time to be around 34 seconds, but most of the time it's around 10 seconds, once it was down to 7 seconds. I imagine these differences arise because the silicone gets molded and perhaps heated up a little bit from use, so therefore the first descend, where the silicone is the stiffest and coldest, takes longer.
     
  8. Ripblade

    Ripblade Forum Resident

    Location:
    The Six
    The first time, the lever is in the up position for a prolonged period, meaning the dashpot is at the top and most of the fluid settles below. After a few uses when the cue is down, the dashpot is also down and the fluid is forced above it. This is, I believe, what accounts for the changes in drop time.
     
    Agitater likes this.

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