Nut Boring

[edgarspencer]

Originally Posted by Dean Romig

Edgar, maybe through your experience in the field you could explain how Parker Bros. attained the “ogee” choke profiles that Austin described and charted and plotted that I received from him. He suggests these profiles were the result of using a “boring nut”.

I've heard the early cutters referred by different acronyms, and how that particular tool got it's name is anyone's guess, but it often came about by what it looked like. This predates a machine called a cutter grinder, and the individual flights may have been individually ground, but as I recall, their early tool was a single flight (cutting edge), which had it curved surface cut by a template, with a large relief for clearing the swarf, or chirps. The individual cutting edge had the advantage of, virtually no chatter, resulting in smooth surface. Aside from the coarse surface, chatter could make the tool go off center. Also, chatter, in a composite barrel would very likely spoil the tube entirely. As an aside, the deep hole drilling bits we made for the oil drill bit companies had an odd number of flights, and they typically were not spaced evenly. We made bits from 8" to a whopping 26" in diameter.
The early, ogee bits also predated expanding reamers. The tool was repeatedly run down the bore, and each successive pass was shimmed to increase the diameter. TPS says somewhere that the shims were pine, but I believe that didn't last long as the pine shim would become spongy with cutting oil, and impregnated swarf debris. I recall reading that the shim preferred was walnut. I believe the English used lignum vitae, which, they believed gave longer, and uniform life. The final bore may have gotten a light hone, but I wonder what the honing stone was. Carborundum, a Union Carbide invention, didn't come along for some time. In fact, the whole science of abrasives was in it's infancy.

Originally Posted by Daniel Carter

Edgar could you detail the process from raw tube to finish boring? The step 1,2,3 etc. of making the tube.

Dan, I believe Parker bought all their barrel tubes in a "near net shape". Several companies supplied tubes and Charles Parker, in his fashion of 'Do what you do best, buy what you don't' seized the opportunity to make his own barrels by buying up the stock of decarbonized steel barrels from Tripplett & Scott, when they failed to win any significant contracts from the war dept. Those barrels were made from a semi-steel compostition, but the low carbon content yielded a very low tensile strength, making the thin walled shotgun tube only suitable for the lowest pressure ammunition.
The purchased steel barrel tubes were made by starting with a hollow billet, and repeatedly drawing it through mandrels, getting smaller, but longer with each pass. The hollow center, while rough at first, was likely bored first then, as needed, the OD turned for concentricity. This drawing process gave a very refined grain structure, and surprisingly, a very straight tube.
The making of damascus tubes is a process pretty well discussed, but involved wrapping the composite material of iron and steel around a mandrel and forge welding it into a tightly knitted, almost homogeneous material. There are several TV shows of competitive blade makers making their own blanks; some better than the dismal attempts of others. The use of flux material seems to weigh heavily in their product.
Parker and most gun makers brazed or soldered their tubes together, then constructed the lugs separately. Highest quality barrels, such as chopper lump, are tubes with the lugs an integral part of the forging, machined and them soldered together. Unlike the barrel failure of the Repro, in another thread, Chopper lump barrels can't "come apart".
The purchased tubes likely only got one, maybe two rough boring operations, before assembly. reaming and chamber cutting was almost certainly done when the two tubes were now a barrel set. Chamber reaming, and finally rim cutting, were done before fitting to the receiver. I've never run across any info describing pattern testing, or regulating, but this would have been done before the strikers, armed with scrapers and draw files, went to work.
Not quite the scale we're into, but our partner foundry, in the UK Midlands poured an HY alloy, pretty similar to HY80, and HY100, and cast the one piece turrets for the Challenger, the British Main Battle tank. Since we were already running a centrifugal pouring line for refinery cracking tubes, I proposed the idea to the MOD to let us in on the bidding for a centrifugally cast HY80 barrel blank for the 105mm NATO Howitzer. We succeeded in getting an initial contract for 40 pieces. Like all 'Gov't' work, they were still in testing when I decided I'd rather be home with my critters.

[Aaron Beck]

Parker and most gun makers brazed or soldered their tubes together, then constructed the lugs separately. Highest quality barrels, such as chopper lump, are tubes with the lugs an integral part of the forging, machined and them soldered together. Unlike the barrel failure of the Repro, in another thread, Chopper lump barrels can't "come apart".

It seems likely to me that the two tubes and lug were brazed together and then finish machined as a unit. All of mine seem to have a brass/spelter coloration indicating a much higher temp than the solder on the ribs. I assumed them to be furnace brazed in some type of fixture

"The purchased tubes likely only got one, maybe two rough boring operations, before assembly. reaming and chamber cutting was almost certainly done when the two tubes were now a barrel set. Chamber reaming, and finally rim cutting, were done before fitting to the receiver."
This choking sequence doesnt seem to allow for concentricty if the barrels were bent to regulate in the last third as is often discussed for point of impact. maybe im mixing things up on this point. Since the muzzles usually appear concentric, I assumed they were choked before assembly. Maybe the pilot can follow the curve as it is slight. Can you clarify Edgar?