It's been a little while since I posted to this thread.
Here's my current shop project, a Cincinnati 12" Universal Dividing Head with lead attachment. This was purchased by the United States Navy in 1940 and, according to the inventory tags was put into long-term storage in 1957. Needless to say, it is covered in nastiness but appears in good shape.
This will be mostly a clean up and deburr operation, it's been banged around a lot over the years. The dividing head and tailstock bases will need to be stoned and possibly scraped as they have been kicked around on a concrete floor. Otherwise, it is complete except for the picking pin and sector and in good, but gooey condition. Here it is almost completely disassembled:
Some of the parts all cleaned up:
A couple of the USN stamps:
Here's a couple pages from the 1940 brochure:
Once I get it back together I'll have to use it to make one of it's own parts. That should be entertaining.
What does a dividing head do, you ask? It divides a circle into almost any number of equal segments, such as for making gears. However, this dividing head goes a step further. When geared to the mill's table with the gearbox and change gears, it turns as the milling machine table moves in X, generating a helix. This is useful for milling helical gears, milling cutters, roots blower rotors, etc.
Technically, dividing heads are "obsolete". I'd say the majority of machinists under the age of 40 can make a spur gear with one and a few can knock out a helical gear in a timely fashion. A select few could turn out herringbone gear that actually works. But what about something even more complicated, such as a centrifugal compressor rotor like this:
This is the point at which most manual machinists would walk away in disgust and a fair number of cnc machinists would too. The remainder would begin biting their fingernails. Talk of "5 axis cnc" would be discussed along with "CAD" and "solid modeling". The idea of machining such a shape manually would be laughed at and I suspect quite a few would use the word "impossible".
Enter the shops of the National Advisory Committee for Aeronautics (NACA) in 1945. The digital computer was still a theory and a functional computer controlled milling machine was almost 25 years away. Airplanes of the day were powered by large reciprocating piston engines. To reach higher altitudes and higher specific power ratings, more efficient supercharger and turbocharger geometry was necessary and was an area of heavy research. This was one of the tasks of NACA.
Here's how NACA made prototype supercharger rotors in 1945. A Cincinatti Universal Milling Machine with a Bridgeport "M" milling attachment on the overarm, a Cincinatti 12" Universal Dividing Head just like mine on the table and a shop-brew hydraulic tracing attachment keeping everything in time:
So, the next time somebody says the only way something can be made is with a "5-axis cnc", tell them the old guys could do it on that old horizontal mill in the back corner under the frayed tarp, because it's true.
