In rifling barrels, a rifling head to hold the cutter is used. This is attached the rod or tube which draws the cutter through the barrel. The rifling head is a steel cylinder, three to 6 inches in length, which will just pass through the drilled and reamed barrel blank.
On the side a slot is cut lengthwise of the cylinder, just wide enough to accept the cutter, which fills the slot from side to side and end to end closely enough so that it has no movement. The slot is cut nearly through the cylinder, seating the cutter as deeply as possible.
The rifling cutter is made from a good tool steel, such as 01 tool steel. It is flat-bottomed and its cutting edge is of the hook type, like a file tooth. The cutting edge has a rake of five to six degrees, both on the face and on the top. The top of the cutting edge is slightly rounded which will fit the radius or diameter of the barrel. The steel cutter is usually about 1 1/2" long and the cutting edge is slightly back of center.
This will leave a space in front of it large enough to hold the chips that are cut in one pass. When the cutter is setting on the bottom of the slot the top of the cutting edge is just below the surface of the rifling head. The cutter is raised to rifling position by placing very thin brass shims underneath of it in the slot. The brass shims should be .0002" to .0003" in thickness.
After the rifling cutter makes a cut in each groove, another shim is placed beneath the cutter. Another cut is then made in each groove until all the grooves are cut to the proper depth. A small hole is first drilled through the rifling head on the bottom of the cutter slot so a small punch can be inserted through the hole to remove the cutter out of the slot in the rifling head. The rifling head is a hollow or tubular piece of high-carbon tool steel that is hardened. The hook-type cutter is set in a port within this tube and the hook or cutting edge is about one fourth of the length of the cutter from the rear end. The rear end of the cutter is beveled off at a thirty-degree angle on the topside and the rear end in the rifling head is beveled at this same angle. The cutter must be beveled on each end at the bottom from a point directly beneath the cutting edge. The bottom bevel is normally ten degrees.
At the rear of the rifling head, a beveled wedge rests beneath the beveled rear of the cutter.
The bevel of the wedge is the same as the bevel on the bottom of the cutter, ten degrees. This beveled wedge is pushed forward by a screw. The rear of the rifling head has fine threads and is tapped into the rear of the rifling head. Turning this screw forward in the rifling head results in pushing the beveled wedge farther forward under the cutter and raises the cutting edge.
A cut is made in each groove of the barrel before moving the wedge farther forward to raise the cutter for a deeper cut. The front end of this hook-type cutter, which is three-quarters of the length of the cutter. This seats against a steel plunger within the tube that has a
coil-spring in front of it.
The front end of the cutter is beveled back from the top at about ten degrees. The end of the spring-backed plunger is beveled at ten degrees in the opposite direction, so that its
included angle with its top surface is 100 degrees. The front end of the cutter is held upward against the top surface of the rifling head. The cutter is normally about 2 to 2 1/4 inches long over all and the rifling head 6 to 8 inches long depending on the caliber. The top or cutting edge of the hook is cut on a radius to fit the bore.
The cutting edge of a rifling cutter is ground and honed to a template. When it is resharpen or honed during the rifling operation its form will not be changed at any point. The cutting edge
has to be kept very sharp and very smooth to do a good job. The barrel steel is tough and tends to tear, rather than cut clean, unless the tool is kept sharp.
The scrape-type of rifling head leaves a better finish in the grooves than does the hook-type hut it is more difficult to keep sharp and requires very careful honing to do a good job. Its cuts by scraping rather than a shearing cut and the shavings are fine.
The rifling head is a hollow cylinder, and is made of high-carbon steel with a slot for the cutter cut lengthwise, about two inches long, on one side. The port has to be cut very accurate, as the scrape cutter must fit it closely with no movement. The cutter cuts in both directions while traveling through the barrel. The rifling head is about 6 to 8 inches long and is threaded internally on both ends. There is a thread at one end for attaching the pull tube, which is used to carry a supply of oil to the cutter.
On the other end, a fine thread is used for the adjusting screw to raise the cutter. In the bottom of the rifling head between the port for the cutter, and on the opposite side, the fine threads for the adjustment screw, a narrow slot is cut length-wise of the head. This is for the head of a screw to set in which is screwed into the bottom of the adjusting wedge.
The cutter body is fitted very close in the slot in the rifling head and the bottom of the cutter body is ground on a taper of about ten degrees from one end to the other. The front edge of this taper is at an exact right-angle fit to the sides of the cutter body. The cutting edge of the scraper on top of the cutter body is not cut at right angles to the sides of the cutter body and rifling head. It extends across the top of the cutter body at a forty-five degree angle to give as much shearing effect to the scrape as possible.
The scraper is at the central point of the cutter body and the body of the cutter is cut away at each side of the scraper to give chip space. The edge that does the scraping has an
included angle of eighty degrees, and the sides sloping down and away from the edge equally in both directions to the top of the cutter body. This scraping edge also has the contour of the circle of the groove diameter of the barrel. The edge should be ground and honed to a template. By doing this its shape will be true and will remain so. The template is cut from thin 01 tool steel.
The wedge, which raises the cutter in its slot in the rifling head, is turned with a circular contour on the bottom to fit the contour of the inside of the rifling head. The top of this wedge is also ground off on a ten-degree taper to match that on the bottom of the cutter body. The thickness of the wedge has its thin end that extends slightly beyond the thick end of the cutter body. This is toward the end of the rifling head to which the pull-rod is fastened.
The thin end of the tapered wedge is ground square on the end. The square end then sets against the square-ended plug, which is backed by a spring. The spring is backed by the end of the pull-rod inside the rifling head. In the bottom of the wedge a hole is drilled and tapped
for a small screw. The head of which fits the slot cut in the bottom of the rifling head. The screw prevents the wedge from turning and is made from 01 tool steel, should be hardened to prevent wear. The adjusting screw for the wedge has an unthreaded portion beyond the threaded part, smaller than the threads. The end of this unthreaded portion is ground square and fits against the large end of the adjusting wedge. When the adjusting screw is screwed forward in the rifling head, it moves the tapered wedge forward and upward under the cutter, raising it as necessary.