Barrel drilling tools. A is plan and detail views of oil tubing used on barrel drills. B is plan and end view of barrel drill while C is underside view of same.
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into the tool post slot in the rest. This tongue is just thick enough to extend a short distance down in the tool post slot and the block is held down by two cap-screws passing down through it and into a bar of steel in the wide groove at the bottom of the slot. This block is drilled and reamed, out beyond the tool post slot, on the exact center line of the lathe, clear through from side to side. This hole is a close fit around the drill drive tube which has no vee-groove in it at this point This block is slotted with a saw-cut from the outer end back through this hole for the drive tube to a short distance back of the hole, the full width of the block. Out beyond the drive tube hole two cap-screws, from top to bottom through the block, clamp the sawed outer end of the block together, squeezing the tube tightly in its hole.
The speed the barrel turns during the drilling operation is high and the feed of the drill into the blank is slow, as you have but one cutting edge on the drill. Oil is pumped under pressure through the tube from the rear end where a connection for a flexible oil tube from the pump is sweated onto the tube. This oil passes through the oil hole in the drill, comes out below the point, and returns, carrying the chips with it in the vee-groove on top of the drill and drive tube. The drill is ground to drill a hole .010" to .012" smaller than the diameter the finished bore is to be made. The blank is carefully centered in the barrel chucks and the hole is started with a center drill and then drilled for a distance with a twist drill to give the barrel drill a true start.
After the barrel is drilled it must be reamed to size and for this operation three reamers are used, a roughing reamer and two finishing reamers, the last really being a burnishing reamer. Reamers are made of highspeed steel and are made with six grooves, except the roughing reamer which may be made with four or six grooves. These barrel reamers have a rather long front pilot, the front end of which is turned down for a short distance so that the tube which draws the reamer through the barrel can be brazed to the reamer pilot. . The ends of the reamer flutes just behind the pilot are given a slight taper to bring the reamer diameter at this point to just under the diameter of the drilled hole in the barrel blank so that the reamer will start to cut easily. The cutting portion or flutes of the barrel reamers vary from 6" to 7" in length. A hole of small size is drilled lengthwise of the pilot from the front end to a necked portion just ahead of the flutes so that oil may be pumped to the reamer through the pull tube. From the end of this hole in the necked portion of the reamers, three small holes spaced equidistant around the neck are drilled at right-angles to the axis of the reamer so that the oil comes out at the front end of the flutes. These front pilots are made to just fit the drilled hole of the blank on the roughing reamer, to fit the rough-reamed hole on the finishing reamer and to fit the finish-reamed hole on the burnishing reamer. The roughing reamer removes .005" to .006" from the drilled hole in the blank, the finishing reamer removes .003" to .004" and the burnishing reamer finishes the bore to size.
Barrel reamers. A is roughing type reamer, four groove, all carried through rear pilot. B is finishing type reamer, six groove, three grooves carried through rear pilot. C is burnishing reamer, six groove, three grooves carried through rear pilot.
The flutes of the roughing and finishing reamers are cut .010" ahead of center as are those of the roughing and finishing chambering reamers, while those on the burnishing reamer are cut on center and finished to shape as are those of the burnish-type chambering reamer. Barrel reamers do not have clearance ground upon them as do the chambering reamers, their clearance is stoned upon them by hand. Barrel reamers with spiral flutes are more efficient than those with straight flutes as they have a shearing cut but these spiral flutes are far more difficult to stone than are straight flutes. Barrel reamers are sometimes made with rear pilots as well as front pilots and in this case the flutes are milled out through the rear pilots so that the chips can pass off the reamer and on down the barrel.
In using the barrel reamers, the reamers are held stationary and the barrel blank revolves at a low speed as the reamer is drawn through the barrel by the oil tube which is attached to a movable carriage such as the lathe carriage in case a lathe is used. A floating connection at the end of the oil tube should be used, so that the reamers are entirely guided by the bore of the blank. The end of the oil tube may be plugged for 2" and a simple universal joint used, attached to this plugged portion, or a floating drive of the type described on chambering reamers may be used. The flexible oil line from the pump is led into the side of the hollow portion of the oil tube ahead of the plugged end through a screw connection like a nipple. This connection must be removed to pass the oil tube through the barrel blank, as the oil tube is brazed to the reamer, and then put in place and the oil line connected to it before starting the lathe.
Shotgun barrels are made from steel tubes and although they may therefore be reamed to size with a series of barrel reamers, such as those used on rifle barrels, they are usually bored with a long, four-sided, square bit of high-speed steel, ground to size on a surface grinder. These bits are 10" to 12" long and have a tapered lead at the front end, about long on the roughing reamer and an inch long on the finishing reamer or bit. The driving rod for these bits is brazed to the rear end of the bit, the opposite end from that which has the tapered lead, and the bits are pushed through the bore as the barrel tube revolves.
A wood packing strip, turned on one side to the contour of the barrel bore, is placed against one side of this bit, its full length, and on the roughing bit the two edges of the side diametrically opposite the side upon which the packing strip is placed do the cutting. Strips of paper are placed between the wood strip and the boring bit to cause it to cut larger after each trip through the barrel.
A wood strip of the same type is used on one side of the finish or fine boring bit but the leading edge of the opposite side has a small radius stoned upon it so that it does no cutting, which is all done with the trailing edge of this side opposite to that on which the wood strip is placed.
Shotgun boring bit, also sometimes used on rifle barrels. End view shows how wood packing strip and shims are used.
A third square bit, the choke boring bit, is used in shotgun barrels. After the finish or fine boring bit is used this choke boring bit which has a tapered lead an inch long which tapers about .050" in this distance is used to bore out the choke portion of the barrel which is not bored out by the finish boring bit, but only by the roughing bit. A wood packing strip is used, with paper shims on the tapered portion of this choke boring bit and this bit cuts upon two edges as does the roughing bit. These shotgun boring bits are run at a low speed and plenty of cutting oil is used. In making the bits they are hand honed after being ground to shape by a surface grinder. They must be carefully checked for straightness. In doing the grind ing, if much stock is to be removed, do not grind a lot off of one side and then off the opposite side but take a small amount off of the first side, then a like amount from the opposite side, then take the same from an adjacent side and the same from the last side and repeat this until the bit is ground to size, as this method of grinding will prevent warping the bit.
Drills for boring out old barrels for relining (the insertion of rifled tubes) may be made from standard, high-speed steel, three or four-groove drills with the regular twist flutes as made by all drill making firms. These manufacturers will grind a pilot on these drills, to order, to fit the old bore of the barrels to be re-lined, or by using an electric tool post grinder you can grind your own pilot upon them. The cutting edges at the rear end of the pilot must be ground with relief, as were the cutting edges at the end of the drill originally. These drills will not drill holes in solid metal but are used to enlarge cored or previously-drilled holes. A carbon-steel shank of any length may be welded to the shank of these drills.
If you wish to make your own drills for drilling out barrels for relining they may be made of a short section, \l/2" to 2" long, of high-speed steel by turning a pilot upon the front end to fit the old bore in the barrel and turning down a short section of the rear end to a smaller size so that an oil tube may be brazed onto it. The body usually has three straight grooves milled lengthwise of it with a fluting cutter. The front end of the lands between these grooves are relieved or ground as are the lips of a twist drill. A small hole is drilled lengthwise of the body from the shank end about halfway through the body and holes are drilled into this at the end toward the point of the drill from each of the grooves so that oil pumped through the oil tube can be forced out into the flutes, washing the chips out of the barrel ahead of the drill and keeping the cutting edges cool. The pilot is grooved with the milling cutter which cuts the flutes so that the chips have a free passage.
After the old barrel is drilled out with one of these drills it is usually reamed with a barrel reamer of the regular fluted t}"pe to straighten the hole perfectly and bring it to size to take the lining tube used.
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Six-groove barrel reamer, of the type commonly used in sets of three, in graduated sizes.