LATEST TRENDS IN MACHINING

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GRINDING WHEELS AND UNIVERSAL GRINDING MACHINES

In 1872, silicate wheels began being produced. A year later, a potter named Sven Pulson made a better
wheel with a mixture of emery and clay, and in 1877, F. B. Norton patented the process. And again, it was
Joseph Brown and his staff who removed the defects in existing grinders and came up with an improved
“Universal Grinding Machine” in 1876. On this machine, the workpiece travelled past the wheel instead of
the wheel traversing the workpiece. The head and tailstock units were mounted on a traversing table.
Adjustment of trips at the front of the machine automatically controlled the table travel. For taper grinding,
slides at the upper table could be angled by means of an adjusting screw. The guide-ways were
protected from abrasive dust, and a water coolant was used. This grinder was the parent of all
subsequent precision grinding machines.
Henry Leland, who had worked as foreman in the Brown & Sharpe shop, and later became the
President of the Cadillac Motor Company wrote later about the grinding machine of Brown: “What
I consider Mr. Brown’s greatest achievement was the Universal Grinding Machine. In developing and
designing this machine he stepped out on entirely new ground and developed a machine which has enabled
us to harden our work first and then grind it with the utmost accuracy....” These new and better grinding
machines facilitated the production of precision gauges and measuring instruments as well as accurate
hardened steel cutting tools such as drills, taps, reamers and milling cutters. A machine shop looked like
one shown in Fig. 1.4.
Fig. 1.4 A machine shop as it looked in 1890
By 1891, an American, Edward G. Acheson, produced a synthetic abrasive of controlled quality by
fusing a mixture of carbon and clay in an electric arc furnace. Crystals (silicon carbide) produced
were of a hardness then surpassed only by diamonds. Acheson called his synthetic material
carborundum. Another American, Charles B. Jacobs, in 1897 produced another synthetic abrasive
by fusing aluminum oxide (bauxite) with small quantities of coke and iron borings and called it alundum.
Charles H. Norton secured the rights to this product and became the man responsible for the production
grinding machine (Fig. 1.5) and better abrasive wheels. First, Norton invented a machine for dynamically
balancing grinding wheels to make them perfectly balanced. Norton also improved the processes of
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MACHINING - LATEST TRENDS
dressing and truing the grinding wheel.
Norton then redesigned the Brown &
Sharpe Universal Grinding Machine
improving the bearings. By building a
heavier, stronger grinding machine,
and by using much wider wheels,
Norton conceived the technique of
plunge grinding. This new grinder was
not only applicable to plain grinding
but also made possible form grinding
by the use of wheels shaped to the
contours desired. In 1903, Charles
Norton produced a crankshaft journal
grinding machine. A wide wheel was
capable of grinding a journal to
finished diameter in a single plunge cut.
The cycle time of the operation was
reduced to 15 minutes, which previously took five hours of turning, filing and polishing. Henry Ford
ordered 35 of these machines for his new Model T production plant. Norton is also credited with
incorporating its own micrometer in the grinding machine to reduce the workpiece by precisely the desired
amount-say 0.00025 of an inch.

GEAR MANUFACTURING MACHINES
Gear mathematics developed through several centuries without having much practical effect on the way
mechanics actually cut gears. Edward Sang produced a treatise in Edinburgh in 1852 that ultimately laid
the groundwork for the generating type of gear cutting.
By 1867, William Sellers had exhibited a milling machine gear cutter in which the sequence of automatic
motions was so controlled by stops that the cutter could not advance unless and until the gear blank had
been correctly indexed for the next tooth. When all the
teeth had been cut, the machine stopped automatically.
Then the molding generating cutter was devised. Instead
of indexing the gear blank, the cutter and the gear blank
were given synchronous motions, so that the two were
correctly meshed together. In 1880, Ambrose Swasey
developed one machine that operated on the “describinggenerating”
method for Pratt & Whitney.
In 1884, Huge Bilgram of Philadelphia came out with a
gear shaper working on the molding generating principle
to make small bevel gears for the chainless bicycle. In 1898,
James E. Gleason invented a machine that generated bevel
gears by using a rotary cutter and a combination of motions-
Fig.1.6 Fellow’s gear shaping machine, 1897 rotary, swinging of the cutter carrier, and lateral. Gleason’s
Fig.1.5 Charles H. Norton’s cylindrical grinder, 1900
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Latest Trends in Machining
machine was fully automatic that provided the manufacturing solution to bevel gearing used in differential
drive. The most advanced gear cutting machine of the molding generating type was Fellows’ gear shaper
of 1897 (Fig.1.6) that was invented just in time to produce gears that would be needed for automobiles.
Edwin Fellows designed the teeth of his cutter in such a way that one cutter could be used to make
gears of any diameter provided the pitch was the same. The only qualification was that its teeth must
be of the specific helix angle the cutter was designed to produce. To make hardened cutters for his
shaping machine, Fellows created another machine.
Hobbing was the last to come. The first attempt to cut gears by using a worm with teeth on it was
made perhaps by Ramsden in England in 1766. In 1835, Josheph Whitworth produced a machine
that would hob spiral gears. But the hobber did not become practical until Pfauter, working in Germany
built a machine with a cutter axis that was not at 900 to the gear axis. There were many problems in
developing the process, but by 1909, there were at least 24 firms manufacturing gear-hobbing machines.

CUTTING TOOL MATERIALS
Robert Mushet first produced the improved tool steel in 1868 in England. That proved to be far superior
to carbon steel used for tool earlier. With this new tool steel, John Fowler & Co. of Leeds turned iron
shafts in the lathe at the rate of 75 feet per minute, and when machining steel wheels in their boring mill they
could make roughing cuts 1/2 inch deep. Frederick W. Taylor (1856-1915) is credited with the revolutionary
research on cutting tool materials. In 1900 Paris Exhibition, Taylor amazed the visitors with chips peeling
away at blue heat from an American lathe while the tip of the cutting tool was red hot.
Taylor was the first to carry out methodical experiments with cutting tools that lasted over 26 years and
cost over $ 200,000 - a large R&D expenditure for the time. Mushet’s steel contained 7% tungsten, 2%
carbon and 2.5% manganese. Taylor with Maunsel White in the Bethlehem Steel Works discovered that
chromium was an effective substitute for manganese used to give the steel self-hardening character, while
giving better performance. They then increased both the chromium and tungsten (the tungsten to 14%)
and added silicon, which was found to increase shock resistance. They found that if a tool is heated to
20000 F (just below fusion point) instead of 15500 F, cutting speed would be increased to 80 to 90 feet
per minute (as against 30 feet per minute in earlier case) before failure occurred in the same time. Addition
of 0.7% vanadium produced further improvement.