150+ Year Old Pratt+Whitney sine bar cut rifling machine ca. 1863 - Coolspring - Part 1 of 2

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Part 1 of 2.

Something interesting shows up at every Coolspring show. At the June 2018 show, the star was this ca. 1863 Pratt & Whitney "Grasshopper" sine bar cut rifling machine.

At the time it was first used, there would have been rows of these machines, driven by lineshafts, powered by either steam or water power. Given the single tiny tool, and the very light cuts taken, each machine would draw only a small fraction of a horsepower.

Here it is driven by an air cooled vertical gas engine, with an antique electric motor for indoor demonstrations when the gas engine can't be run.

It is cutting 12" RH twist, 6 starts, for .308 Win. It cuts on the pull stroke, to avoid bending of the boring bar and possible tool chatter.

Note the elliptical gears, which vary the crank rotational speed to keep the tool speed nearly constant during the cutting stroke.

The sloping ramp (cam) which rotates the tool is called a Sine Bar. At least theoretically, it could be made curved, to provide progressive twist.

The machinist is advancing the cutter manually, by screwing in a wedge below the cutter, but the machine has provision for automatic tool advance, via the extra ratchet mechanism at the end of the machine. The tool feed unit presses on a pushrod sticking out of the boring bar, raising the wedge. It even stops advancing the tool automatically when correct depth has been reached.

The 19th century was an era of tremendous technological progress, when common people came to realize the benefits and liabilities of technology. This machine demonstrates both.

Sine Bar cut rifling machines are still being made, to manufacture match grade cut barrels. Several of these are on Youtube. One example that is clearly explained is:    • Sine Bar Cut Rifling Machine Blake Ma...  

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