Historical Development of Deep Hole Drilling

History of Gun Drilling
Gundrilling although unbeknownst to the contemporary engineers, began its journey in the late 19th and early 20th century. Early gun barrels were manufactured by either by roll-forging or “Damascus” spiral welding. As the propellants became more powerful with innovations - the need for stronger, more dependable steel barrels grew. Alloyed steel had become quite widely used by then due to its superior mechanical properties. And hence, drilling of alloyed steel bars became necessary to extract better performance outcomes.
For long holes, twist drill-bits were welded to long shafts. That was a task in itself - laborious, time consuming and prone to a lot of rework & rejections. On top of it, the drill would drift and wander as it progressed into the deeper hole depths.

But then, wood-working industry had quite well-established methods long hole drilling methods that employed long, straight grooved or D-section augers. Such tools, ground with eccentric / off-center cutting edges, had been found to provide pretty straight, controlled hole geometry. Drawing from this idea and implementation into metal cutting - greatly improved the hole quality. But, it was still an expensive and laborious affair.

The final step to that brought to form the modern-day gun-drill took place in 1930s with the idea of affixing the cutting-bit to a formed tubular shank through which the coolant could be passed, which would then flow through a hole in the cutting-bit - to lubricate cutting action, cool the work-piece & tool, and flush the chips out.

History of BTA Drilling
While Gun drilling proved to be a robust operation, and continues to be the preferred operation for deep hole drilling, better surface quality of the holes became necessary for some applications. The fact that the generated chips that are evacuated through the gun-drill - remain in contact with the work-piece while being forced out by the high pressure coolant, was causing micro disturbances to the surface roughness of the holes. While this was not important for most applications, the need for a different type of process that creates sufficiently nice surface finish, but not as fine as honing, became relevant.

As a result - a new deep hole drilling method was developed around 1940 by the "Boring and Trepanning Association" - which was dominated by the now liquidated company Gebrüder Heller in Bremen Germany.

As the developments continued - the grooved tubular shank used until then - was replaced by a circular tube with a closed cross-section - which was more torsionally rigid, and coolant flow was reversed i.e., coolant came from outside and took the chips into the tubular shank - effectively eliminating rubbing of the chips with the drilled hole. And the new process was named 'BTA deep hole drilling' by around 1950s.

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