Tuesday, March 29, 2011

Computer Numeric Re-Considerations (IV)

Post four in this thread examining the issue of computer controlled equipment in the woodworking context. Numerical Control (NC) refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via hand wheels or levers.

Early NC machines in the 1940's and 1950's accomplished the information storage by way of punched tape, which, as the name suggests, consisted of a long strip of paper in which holes are punched to store data. These are now long obsolete. One could argue that forms of the idea central those punched tapes appeared on the scene hundred of years earlier. As far back as the medieval period, mills with water driven shafts festooned with protruding elements made for the operation of trip hammers for forging on a predictable pattern.

In 1801 Joseph Marie Jacquard invented a device which allowed punch cards to operate weaving looms. This device, the Jacquard Loom, simplified the process of manufacturing textiles with complex patterns- here's a picture of an example of that sort of loom, from a plant in India:

Changing the pattern of the loom's weave was no more difficult than changing the punch cards out for different ones. This concept was an important one, it should be noted, in terms of the development of the computer. The real development of punch cards happened when Herman Hollerith developed his tabulating machine in the 1890's so as to enable the data from the US census to be tabulated in a much quicker time frame -from an expected 10 years down to a matter of a few months. Here's Herman:

Hollerith, in 1911, merged his Tabulating Machine Company with two others, the International Time Recording Company, and the Computing Scale Company, to form the Computer-Tabulating Recording Company. The new company (CTR) came under single management for the first time in 1914, when the company had 1,300 employees. It was in that year the late Thomas J. Watson, Sr., a salesman of cash registers, joined the firm as general manager, and soon became its president. In 1924, the name International Business Machines Corporation was adopted. That's IBM, in case you missed it. This proprietary punch card technology of the IBM Corporation saw use during the second world war to aid, amongst other things, the Nazi's in compiling detailed information on the Jewish population and running all those 'special' trains on time - a story told most persuasively and in great detail in Edwin Black's brilliant investigative work IBM and the Holocaust. Each of the death camps, for instance, had it's own Hollerith Tabulating Machine. That's a book definitely worth a read, guaranteed not to cheer one up too much.

Right, back to our story. In previous posts I have looked at the question of hand work vs CNC-machined work in terms of creative expression, and in the immediately preceding post, I mentioned the fairly obvious advantage CNC gives when the maker is faced with producing large numbers of duplicate parts.

The person credited with pioneering Computer Numerical Control systems (CNC) for machine tools was a certain John T. Parsons. Like so many other technological developments, the impetus was the development of military hardware. In 1946, together with his employee Frank Stulen, Parsons developed a punch-card operated equipment to solve the challenging machining operations inherent in producing the complex curves of a helicopter blade. As Parsons notes in an interview where he recollects the development process:

" To define an airfoil template, they gave us 17 points between the radii on the upper and lower surfaces. The coordinate points were different for each of the two surfaces. Then you had to take a French curve and connect those points. It wasn't accurate, and you didn't know the accuracy of the French curve between the coordinates. So I asked Stulen if he could use his college education, something I don't have, and give me 200 points along the radius of each surface, which he had no problem doing. He made up a chart describing X axis and Y-axis coordinates for a milling machine. Then, using a Bridgeport mill, we put one man on the left-to-right axis, and one man on the in-and-out axis. We didn't have to worry about the Z axis because we were using a 0.050" thick steel template. That's the way we made templates in the late 1940s. That's what prompted the work to do it automatically."

In 1948, Parson's company was awarded a contract to develop a related military product:

"the innovative and challenging tapered wings for military aircraft; they won the contract because they developed the computer support to do the difficult three-dimensional interpolation for the complex shapes, as well as the 800 steps long production cycle for the wing manufacturing."

I think an important point in regards to the adoption of NC, and later CNC techniques, is that the development was driven by the difficult technical challenges that were defying solutions by conventional means. These machines were not initially considered in light of their effect upon labor conditions and production. The new types of aircraft and missiles developed after WW II, like jet-engined planes for instance, required materials and construction that made them both extremely strong and as light as possible. Attempts to produce the tapered complex wing shapes by conventional fabrication approaches described in the foregoing quote had in fact resulted in utter failure. Parsons was hired to to try and solve the problem after these conventional approaches were clearly not getting the job done - the wings of the plane in question, when produced by templating and standard mill work techniques made for a plane that was so heavy it couldn't get off the ground.

In time, MIT became involved as Parsons realized one of the design challenges of the technology involved developing servomotors which would allow for accurate positioning and smooth cutting actions. As noted in the Wikipedia article on Numerical Control,

"Since the mechanical controls did not respond in a linear fashion, you couldn't simply drive it with a given amount of power, because the differing forces meant the same amount of power would not always produce the same amount of motion in the controls. No matter how many points you included, the outline would still be rough."

This casts an interesting light on the question of human sensitivity to material vs the apparent 'blunt instrument' of the machine. I'll set that aside for the moment however.

MIT and Parsons got into a tussle over the development of CNC, but in the end Parsons was granted the first patents for the technology in 1958. It took many years however before CNC-manufacturing caught on to any significant extent, a problem that Parsons put down to the "computer people":

" The slow progress of computer development was part of the problem. In addition, the people who were trying to sell the idea didn’t really know manufacturing—they were computer people.
The NC concept was so strange to manufacturers, and so slow to catch on, that the US Army itself finally had to build 120 NC machines and lease them to various manufacturers to begin popularizing its use."
In time, those CNC-operated machine tools did catch on, and became much the norm in the machine tool industry. If you own any power tools built since 1980 or so, you can be fairly certain that CNC processes were employed at some point, most especially in the tool and die portion of the job, where the casting molds were developed. Many hand tools now are being produced by way of CNC as well- I would cite the products of Lee Valley and Bridge City Toolworks as obvious examples, where CNC machine tools make the products themselves to one extent or another.

It turns out that the advent of CNC came to be perceived by certain folks as having other sorts of interesting 'advantages' besides improving production capability and quality. In the next post I'll delve into that matter in more detail.

Thanks for coming by the Carpentry Way today.

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