I was reading something on the net about how there were few specifications for arm bearing friction.
Here is a quick and easy way to test your tonearm to get some idea of how much force it takes to move the vertical movement bearing.
Take a sheet of photocopy paper. It is usually around 80g per square meter, that is, 80,000mg.
As there are 100cm per side in a square meter, this means that every square centimetre weighs 1/100 x 1/100 x80,000 mg, which is 8mg.
So if you cut a strip of paper 1cm wide, each 1cm of length is 8mg.
If you cut 3cm, that is 24mg.
Make a fold at 2cm to create an L shaped tab you can hold.
Balance out your arm then, holding the paper by the tab with tweezers, gently lower it onto the arm., trying not to push down. As you do this (and also when you lift it off) the arm should move. If it does, then the force at the headshell to overcome static bearing friction is less than 24mg.
This doesn't say how much friction there is, when the arm is in use. It will be lower, though not by much. Most arms use ball bearings or unipivots which have very low friction coefficients generally, so the main factor is the load on the bearing, ie how heavy the arm is and how much the bearings are tightened.
On this test, a recent RP1-xg I refurbished moved with less than 16mg, (ie two squares). It is hard to get a reliable result below this, as it is hard to see the movement of the arm, and also to be sure whether or not the act of placing the paper has contributed an additional force.
Friction, as such, is not really the main problem for arms, provided it is low. A notchy or sticky bearing is far more problematic. Also internal wiring which is too stiff contributes a significant torque which acts arbitrarily, affecting both tracking and anti-skate. Some designs even use this as an anti-skating method. Arms with wiring external to the bearing are even more susceptible to this problem. The closer to the bearing the wire is routed, the better, as any turning effect is reduced.
