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

I just read Mikey's review of the Kuzma 4Point in the September Stereophile.

I am always intrigued by clever design and technology. (I really enjoyed reading and understanding the design of the Well Tempered Turntable and Arm. Also the Garrard Zero 100 from earlier years.) The review suggested that the Kuzma 4Point was innovative and clever in its design.

But for the life of me, I could not understand Mikey's description of the bearing. It was completely opaque to me.

I am glad to find that some of you have some experience with this arm. Can you share with me your understanding of how the bearing is implemented? I am intrigued and itching with curiosity!

Thuchan -- "Don't take me wrong but it seems funny to me that MF discovered the 4point as the last in the row :-)"

You make a good point about too much time passing between reviews to make a reliable comparison.

Part of it must be that the 4point was introduced years after the Airline. Or so I seem to recall.

Aha! Finally, I understand it. Thank you Hiho for your pics and comments; they really helped me a lot.

In your post, you have "2points + 2points = 4points" pics. The "4points" pic shows the pivot structure with two vertical cylinders. The big cylinder is clearly for VTA adjustment.

The small cylinder is a hollow sleeve that encloses a vertical post upon which it rests. The hollow sleeve contacts the vertical post inside it at two points, as shown in the second "2points" pic, where two hands are holding an unpainted cutaway cylinder horizontally. The two points are (1) at the end of the post and (2) from the side, with a spike touching the post near the other end of the cylinder.

The first "2points" pic shows the arm upside down, revealing two small spikes (like rose thorns) sticking up. These apparently will rest in two cups, shown in the "4points" pic. The two cups are in the horizontal base attached to the smaller vertical cylinder.

Thus, the arm will rest on the two rose thorn spikes on the base attached to the cylinder. And these spikes allow the arm to pivot the head up and down. Additionally, with the base attached to the smaller cylinder, the arm can pivot horizontally because the smaller cylinder can turn about the post that is captured inside of it.

(As you point out, the partial cutout in the post, where the second "point" contact is made inside the cylinder, causes the horizontal pivot movement of the arm to be limited to only 45 degrees.)

I can also identify now the damping troughs, both of which are accompanied by screw-rods secured by knurled-wheel nuts.

Upon further thought, I perceive that the second "point" inside the cylinder must be weight loaded because the arm is resting on the base to the side of the cylinder. This would cause the cylinder to want to tip sideways, and the second "point" inside the cylinder prevents that, keeping it vertical.

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.

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