This is the original design from my Kickstarter project. I still think it's the best. For me good design is all about balance and simplicity. The Lambda Brass is an excercise in both.
The brass used in the ring is predominantely a copper alloy, and heavier than anything but much more exotic metals. Brass cuts easily, which means it machines VERY consistently. Tougher materials wear the tools faster which leads to quicker changes in part dimension and "out of tolerance" conditions.
The 6061 aluminum spindle is strong, light weight, and raw machined aluminum. I normally nickel plate all of my aluminum parts, but it's just not necesary here. I also really like the contrast of the "cool-colored" aluminum next to the warm brass.
Of course the ruby is the ultimate in performance and awesome...can't beat that combination. It's a little bit fragile if you compare it to a Mac truck, but a little bit of knowledge and care will keep it spinning for a lifetime. I mean, it's nearly as hard as diamond and that is "forever."
Ruby and stainless tops are carried in inventory. Al2 O3 and SiC tops are assembled to order and will delay shipment by 1-2 days. Now you can choose between instrument ruby, stainless steel, Aluminum Oxide (white), or Silicon Carbide (dark gray). Aluminum Oxide and Silicon Carbide are considered "ceramic" ball bearings.
You will not notice a difference in performance between the contact points, but some people enjoy the difference in appearance, and science behind the materials.
Instrument Ruby is a crystalline form of Aluminum Oxide and called Corundum. Corundum is a naturally occurring mineral, but instrument rubies are synthetic. This material has the distinction of being the very first gem mineral artificially created in a laboratory. A small amount of impurity (Chromium) gives ruby the distinct red color.
Stainless Steel Bearings a good choice if you never want to worry about breaking the contact point. The steel balls used in the Lambda tops are 440C Passivated Stainless Steel. This material is hardened and highly corrosion resistant. 440C is the most common material used in high-quality bearings. It's superior to chrome steel, but not the most exotic steel bearing material.
Aluminum Oxide (Al2O3) balls are classified as a "ceramic" because they are sintered from a powder base. Chemically, this is the exact same material as ruby or sapphire, but it is not a crystalline structure. Al2O3 is most commonly used as an abrasive in the manufacture of sand paper. It is also the coating that grows on aluminum when it is anodized. These ceramic balls are typically used in bearings that see extreme temperatures.
Silicon Carbide (SiC) balls are also "ceramic" and used in even more extreme bearing applications. SiC is heat tolerant up to a staggering 1800*C. It's commonly used in the manufacture of ceramic brake discs, ballistic plates in bullet proof vests, and LEDs. I recommend SiC for the extremely heavy tungsten top because it is the most durable of the three exotic contact point materials.
Durability: Contact points cannot be repaired or replaced. They are permanently press-fit into the spindle to achieve the desired degree of balance and accuracy.
The stainless bearing is the most durable option across the board. Clumsy? Steel. Got kids? Steel. Will you cry if the contact point breaks? Steel.
So why all the fuss about exotic contact points? The difference is the ruby and ceramics are MUCH harder than steel, and will spin more efficiently. It's like the difference between ice skating and snow skiing...both water...both fairly "solid" but which one is more efficient for sliding on?
A ruby is a ruby, and if you abuse it...it can chip. It's like a wine glass; works fine until you drop it. The ceramics can also shatter if subjected to enough force, but are generally tougher than the ruby. Silicon Carbide is the most durable exotic material.