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VPI JMW 10.5 damping oil question

I have another VPI JMW 10.5 setup question. I was experimenting with adding damping oil. According to the setup manual, I should fill the oil cup ¾ full such that it will not overflow when the arm tube is set in place. The underside of the arm there is a half-sphere object with a deep conic indentation in the middle. When the arm tube is set in place, the indentation sits on the pivot bearing so I assume the surface of the half-sphere should be immerse in the oil cup. What puzzles me is that no matter how much oil I add, even up to the rim of the oil cup, no part of the arm tube ever touches the oil. Is this normal? If so, how does oil damping work if nothing touchs it.
sidssp
dopogue
1,773 posts
 
I have this arm, and that part of the arm tube definitely contacts the damping fluid. No idea why yours doesn't. Check with Mike at VPI.
shamburg's avatar
shamburg
37 posts
 
Mine doesn't touch the oil either. I always assumed the oil damped the arm/pivot unit–not the arm by itself.
sidssp OP
1,077 posts
 
I spoke with Vpi. The underside of the half-sphere should definitly touch the damping oil. There is a setscrew on the top of the arm base right next to the arm wire. Turning this setscrew can lower the arm tube into the oil cup and control the amount of damping.
twl
3,251 posts
 
If the paddle doesn't touch the silicone fluid, then how in the world would the damping work? Come on guys, think about it.
jackcob
37 posts
 
Sidssp:
Are you sure that no part of the arm is touching the fluid? Mike from VPI told me to add enough fluid so that when you lift the arm off the bearing/pivot, a small "thread" of fluid extends about 1 1/4" before breaking. I use a little less fluid, but even when I use very little, you can see a thin thread develop between the male and female bearing when you lift off the arm. I assume that if there were "no contact", no fluid would stick to the top/male bearing when the arm is lifted off.
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