How were things manufactured before CNC?

[Curl]

I saw a video from the 30's with some very nice looking involute helical gears in a differential assembly. I can't help but wonder how these were made back then without CNC machines. Surely the tolerances are tight for such parts, so what was the secret to making these? Does anyone know?

 

[Ranger Mike]

CNC typically means Computer Numerically Controlled. Industrial computers really became wide spread after World War 2. Before that, high tolerance manufacturing of precision parts was possible by using the most advanced computer of its day..the human brain. If you think about it, machining complex parts is a function of moving a “ cutter head” in a specific XYZ path. Pre computer age machine tools did this with mechanical means controlling the cutting speed and feed rate with various mechanical mechanisms. There was a lot of complicated “ watch works” parts required to do this and in some cases you had machines dedicated to machine one particular feature of a gear or piston and the part was “ transferred” to the next station for another machining operation. This is where the huge manufacturing plants evolved since they housed many “transfer lines” . Look at the old photos of GM and Ford in Detroit. Long , narrow two and three story brick buildings, many city blocks long. Anyway, with the introduction of a hardened computer all these mechanical methods could be replaced with a much smaller CNC Machine Tool capable of performing many different operations.

 

[Astronuc]

Before fully integrated CNC, there were craftsmen machinists and tooling manufacturers. Some processes were semi-automatic, but there was a lot accomplished by skilled craftspersons.

 

[pantaz]

If you're really interested, here's a good place to start:

Cornell Reuleaux Collection of Kinematic Models
http://www.mae.cornell.edu/about/reuleaux.cfm

"Kinematics flourished in the 19th century as machine inventors learned to transmit information and forces (power) from one element in the machine to another. Scientific American featured a new invention in every issue. Steam-and water-based machines revolutionized the 19th century, but both of those energy sources generate circular motions, creating the need to convert these steady circular motions into nonsteady linear and curvilinear motion for machine applications. The challenge to create input-output kinematic devices that could convert circular motion into noncircular, complex, three-dimensional, intermittent motions attracted both practical inventors as well as mathematicians. Thousands of mechanisms were invented, designed, and built, nurturing the widespread use and manufacture of machinesaa process analogous to the plethora of electronic circuits in the early 20th century and software in the late 20th century."
-- http://www.mae.cornell.edu/about/reuleaux.cfm​