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

Jfrech: Two bearing points are the horizontal plane and are permanently hidden, and two points are in the vertical plane. The latter are clearly visible and are akin to two inverted unipivots. It's obvious when you see it.

Kuzma dealer.

Hiho, thank you as well. The photos are very helpful.

Jfrech: "So Mikey kept saying chatterless...seems like there can be chatter in this bearing too...maybe he means less via the 3 points in a cup. 4th on a post..."

I think you got it confused. It should be 2 points for vertical and 2 points for horizontal movement.

The whole point (pun intended) of this design is not to use any ball racing bearings and/or gimbal bearings. The concept is derived from unipivot style bearing but using 4 of them. It's like 4 unipivot arms merged into one to combat unnecessary azimuth/torsional movement. 4 spikes in 4 cups, very simple and effective and cleverly arranged. Check pictures below.

The two spikes are for vertical movement so there are only two contact points, low friction and no ball bearings that can chatter. On the pivot post, the female part, one spike is on the top for horizontal movement and another spike for keeping it from swinging around. So the whole column can only rotate about 45° which is just enough for a pivot to swing from rest position to the spindle. It's an ingenious design that allows the lowest contact points (4) without resorting to a unipivot (1) that exhibits azimuth movement. On top of that, both vertical and horizontal motions have fluid damping troughs so each can be damped individually, whereas typical unipivot or gimbal arms damp both at the same time. Again, clever. Also notice the two cups are located not at the middle cross section of the column? It's intentionally off-centered so whole arm's mass is concentrated at the horizontal spike. Essentially all 4 points are preloaded with mass. Simple and clever. Oh, don't forget the two spikes for vertical bearings are positioned 19.50° off-centered (less than typical 9" arms at 23°) to match the headshell so VTA would not affect azimuth angle. Also nice. The bigger counterweight is on the same horizontal plane as the two vertical spikes so render the arm neutral balance without any pendulum effect, low inertia. Good.

Some more pictures:

4 point locations & Specifications

I am not surprised by the positive reviews as it clearly shows, to me at least, good engineering in many parameters of a good tonearm. The designer has done his homework. As for the negative reviews, it maybe is in the material and execution, over damping, wires, energy transfer, etc..., anything is possible. Since I don't have the arm to play with, I have no comment on the sound. The above is only my observation. From what I saw, Mr. Kuzma has earned my respect as a designer. Tonearm design is fun to look at and think about for me. As a student of the art, it's nice to see some clever thinking these days.

Have fun.

_______

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 my view the use of the word unipivot is misleading - the 2 vertical bearings are like a double knife edge as in the early SME's except that they are points/cups instead of knife edge/groove. Unlike a true unipivot the whole arm tube will chatter with a low compliance cartridge..