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Testing tonearm bearings

I know these are good tests for tight bearings, but what about loose ones, where the looseness is otherwise imperceptible?
 
dbxdx5 said:
That doesn't mean the bearings don't need adjustment. They should be perfect from the factory, but that's not always the reality.
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You should not need to adjust arm bearings actually Technics for example are set from the factory with 1 micron clearance which is impossible to achieve yourself and not advised at all. If Jelco need adjustment this alone ie needing home users to attempt to adjust the bearing would make the Jelco an inferior arm. I dont believe that Jelco advise or expect home users to do this. More likely the Jelco is just a higher friction than the Technics as the Technics is one of the lowest friction arms out there. Advising people to unscrew and adjust bearing like the Technics or Jelco is ill advised as these bearings are easily damaged and getting load correct at home is almost impossible.
Chris
 
I didn't recommend you (or anyone else) try to adjust the Jelco bearings. I said that yours may not have been adjusted properly from the factory. That would not mean it's an inferior arm (though it may be). It's unrealistic to expect 100 percent perfect quality control from any manufacturer. See, you could be right that the design of the Jelco arm is such that there's more bearing friction than in the Technics. But you're making an assumption based on a sample of one. One way to know if you're right is to bring the arm to someone who possesses the skill necessary to check and adjust the bearings in order to rule in (or out) a design deficiency. Or, if it were me, I'd contact Jelco, either directly or through a trusted distributor, explain how I checked the bearings, describe the results, and ask whether they are within the tolerances that have been spec'd.
 
dbxdx5 said:
I didn't recommend you (or anyone else) try to adjust the Jelco bearings. I said that yours may not have been adjusted properly from the factory. That would not mean it's an inferior arm (though it may be). It's unrealistic to expect 100 percent perfect quality control from any manufacturer. See, you could be right that the design of the Jelco arm is such that there's more bearing friction than in the Technics. But you're making an assumption based on a sample of one. One way to know if you're right is to bring the arm to someone who possesses the skill necessary to check and adjust the bearings in order to rule in (or out) a design deficiency. Or, if it were me, I'd contact Jelco, either directly or through a trusted distributor, explain how I checked the bearings, describe the results, and ask whether they are within the tolerances that have been spec'd.
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It is not exactly high friction just higher than the Technics, maybe double. That is still low so probably in spec, just not as good as a Technics. I have three Technics arms and friction for then all is the same. Most likely is the Jelco is just more as most arms have higher friction than Technics.
Chris
 
Great thread @Grbluen!! It provided useful information.
I'm not worried about the uni-pivot on my VPI because the arm is basically balancing on a very sharp spike, so how much friction can there be. I guess that's the point (pun intended :D) of an uni-pivot but I've been very curious about traditional bearings and definitely wondered about the condition of the 40 year old stock bearings on my Sansui 838.

I had some time to kill today so first I tried the the KAB method that @mackat linked and it passed with no problem. It also easily passed the breath test @ConradH mentioned. Then I did the paper test @The Slider suggested and to my surprise it also worked like a charm. A tiny piece of paper actually did make the tonearm drop.

Then I decided to step it up a notch. I wanted to see if something that definitely weighed on the very low side of the single digit milligram range would move the arm. My scale only goes into the hundredths so I had to improvise a bit. I weighed a lead pencil insert and came up with a weight of .08 gr. So it follows that 1/10th of the length of that insert would weigh ~8 mg so I broke off a tiny piece that was much less that 1/10th (probably closer to 1/20th or ~4 mg). As expected when I placed it on the scale there was no reading at all. But when I placed it on the floating tonearm it dropped!. Not bad for a stock tonearm bearing that is at least 40 years old!

By all accounts these arms/tables were made for Sansui by Micro-Seiki.

Gotta hand it to Micro-Seiki, I'm impressed!





For scale:
 
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cafe latte said:
It is not exactly high friction just higher than the Technics, maybe double. That is still low so probably in spec, just not as good as a Technics. I have three Technics arms and friction for then all is the same. Most likely is the Jelco is just more as most arms have higher friction than Technics.
Chris
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I wrote this a long time and I did not realise that the the difference in bearing friction wad huge between the jelco 25 and Technics 7mg.
Chris
 
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