The irony in manufacturing small parts is that smaller does not always mean simpler. In general, when you have a smaller quantity or size of something, it is easier to handle, or easier to count. However, manufacturing small metal parts is anything but simple. Even the part numbers can become quite complicated.
Manufacturing small metal parts on Swiss machines often involves working with features that require custom made cutting tools. Larger parts can use tools of various sizes, because they can be used in multiple passes or operations to create the larger form. With Swiss parts, the features are so small that standard tooling may not be available, or performing the operation with the same method as a larger feature is not practical.
Rotary broaching tools are available with various features to help the machinist accomplish these smaller forms on the Swiss CNC or screw machines such as Citizen, Star and Tsugami. The primary size of the tooling is reduced for Swiss machining. Standard 8mm diameter shank broaches come in standard 1.25” and 28mm overall lengths. This is considerably smaller than the industry standard .50” diameter shank and 1.75” overall length.
The length of clearance ground into the broach is also reduced. Because most forms do not need to be broached much more than 1 times the diameter, most standard broaches are ground with a clearance length 2 times the diameter. Additionally, hex broaches from Polygon Solutions usually feature a pressure relief hole. However, in very small broaches, this hole cannot be added without ruining the integrity of the broach. Therefore, very small Swiss Rotary Broach tools do not always have this hole. If you still want the hole added, or do not want the hole added in a larger broach, simply request that when ordering.
Part preparation in small holes may also be more difficult. The ideal pilot hole for a hex broach includes a chamfer at the opening, and a recess or edge at the bottom of the hole for chips to break free. Because standard tooling will not fit into the bottom of these holes, other solutions need to be considered. For example, can the chips be compacted into the bottom of the hole and remain there as part of the finished product? This may not be practical for a bone screw, but it may be acceptable for other commercial applications. Also, due to the small size of the part, would it be acceptable to change the hole to a through hole? The minimal amount of wear and tear on the tooling may help solve various problems.
Manufacturing Swiss sizes hexagons is likely to be as much of a challenge as a typical socket head screw. But consider some of the options from broach manufacturers to help you. Maybe this time smaller will be simpler.