Kuzma 4Point vs Airline - is it worth the upgrade?

In this bearing set up, the positioning of the two rose thorn spike tips must be exactly in the centers of the two cups in the base. In a normal unipivot, the spike point "finds" the center of the cup, but with two spikes, one spike will probably find its cup's center while the other spike will fall where it may.

Of course it is very important that the other cup be centered exactly where that other spike falls. If it is off by even a little bit, there will not be a properly rigid contact, and chatter could result.

In other words, the distance between the tips of the spikes must be exactly equal to the distance between the centers of the cups. They must not be off by even a little bit. I see from the first "2point" pic that one spike tip position appears adjustable since there seems to be a set screw for the spike.

Perhaps there is some step in the setup procedure that ensures both spike tips are completely centered in their cups.

Dover: "Unlike a true unipivot the whole arm tube will chatter with a low compliance cartridge.."

Conceptually similar to SME but I don't see how two needle points sitting on two cups with the entire mass of the arm preloading the bearings can chatter or chatter to the level of conventional gimbal bearings. I agree with Brian.

I did not say it is a unipivot but clearly and explicitly the designer had the concept of unipivot tonearm, which Kuzma also makes, in mind. Check specification page. (Sorry about the early post that I uploaded the wrong spec image.)

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Hi Essential, yes I agree with the line analogy, but my thought was that with 2 points of contact the arm could potentially chatter - does seem a halfway house between captured bearing and unipivot, which may be a good thing, but I guess my point was it is not a unipivot.

Jameswei: "In other words, the distance between the tips of the spikes must be exactly equal to the distance between the centers of the cups. They must not be off by even a little bit. I see from the first "2point" pic that one spike tip position appears adjustable since there seems to be a set screw for the spike."

Very good point, Jameswei. I think as long as one spike/cup contact is secured, the other one may fall wherever it may be in the cup and still not chatter, though not as elegant. Another solution is on the female side to be one cup and the other a groove and this way the tolerance need not be so tight. The Morch DP6 tonearm is a two point bearing design and one spike/cup is height adjustable in order to change azimuth. Perhaps the set screw on the spike of the Kuzma 4Point is for that too.

The Origin Life Encounter tonearm is also a two point bearing design that does not allow azimuth change at the bearings and they are factory set to ensure perfect contact.

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Hiho, I was not able to connect using your "Origin Life Encounter" link.

Perhaps you wanted us to see this page --

http://www.tonearm.co.uk/dual%20pivot%20explained.pdf