wash out easily with the flow of oil. If this is not done a taper reamer has a tendency to allow the chips to pack in the flutes. A catalog cut of Morse or Brown & Sharpe taper reamers for reaming sockets or spindles for these tapers will show the lands of the roughing reamer nicked as mentioned. This is especially desirable in a machine-drive reamer and the roughing reamer. is practically always machine driven. These nicks or grooves around the reamer may be %6" to %" apart.
In cutting the flutes of a reamer the face or cutting edge of the flutes should not be on the center line of the blank, with the exception of those on the burnishing reamer. This cutting edge should be about .010" ahead of center, which gives a shearing cut and prevents the reamer digging in. This feature, combined with the eccentric relief stoned on the flutes in the hand-finish stoning, helps prevent chatter. This feature is illustrated and described very well in the Greenfield Tap & Die catalog in describing their "Reamrite" hand adjustable expansion reamers.
As in cutting our reamer flutes an uneven distance apart we cannot have them all with their cutting edges .010" ahead of center we cut #1 flute in this position. The next flute, #2, is cut .008" ahead of center, #3 is cut .006" ahead of center, but on #4 we return again to .010" of center because #1 and #4 are directly opposite to each other and by making them the same distance ahead of center we are able to get a truer micrometer measurement of the reamer for size, therefore #5 flute is cut .008" ahead of center as was #2 and #6 flute is cut .006" ahead to match #3 flute. The four-flute roughing reamers may have their flutes cut .010", .008", 006" and .004" ahead of center, respectively as their diameter need not be measured accurately closer than .001" as it is made .010" to .015" smaller than the finish chambering reamer.
The roughing and finishing reamers are fluted with a standard reamer-fluting milling cutter of sixty to eighty degrees included angle as made by the tool companies that make milling cutters, but the burnishing reamer is fluted with a radius, cutter of the convex type, with its center set exactly on the center of the blank. The lands left between the flutes are next milled at the top, on each side of the center, so that the center of each land is left as a sharp, or almost-sharp edge, with an included angle of about 120 degrees.
A is toughing type chambering reamer, four groove, with floating drive for machine use. Driving sleeve comes far enough down on the reamer to act as a stop for depth. B is finishing type chambering reamer, for hand use. C is burnishing reamer, without pilot, with long shank for use in chambering a barrel screwed up in the receiver.
After the burnishing reamer is hardened and then tempered at a light straw color, about 420 degrees Fahrenheit, it is ground cylindrically, on centers, until it is about .002" oversize. This leaves a radius on the top of the lands and the side angles milled on the tops of the lands are now stoned by hand until the center of the lands are sharp. The reamer is still oversize and a slight flat is stoned, by hand, on the sharp edges in the center of each land, reducing the reamer to exact size.
Roughing and finishing reamers are left .015" or more oversize when the blank is turned to shape and after being hardened and tempered they are ground, on centers, until they are within .002" to .003" of the proper size. Clearance is then ground on the lands back of the cutting edge but this edge itself is not touched with the grinding wheel. This unground cutting edge on each land is then stoned with a fine hand stone in an eccentric shape until the reamer is brought to size.
Some gunsmiths use a separate throating reamer, of six flutes, tapered with an included angle of about iy2 degrees, to throat the rifling just ahead of the chamber to give clearance for the bullet when a loaded cartridge is in place in the chamber. These reamers have flutes
Detail of how the teeth of a finish-type learner are stoned.
of the same shape as the finish-type chambering reamer with the cutting edges .010" ahead of the center of the blank and the flutes unevenly spaced as are those of the finish chambering reamer. These reamers have a pilot which fits the bore closely and rides on top of the lands.
Other gunsmiths, in making the finish chambering reamer, make this throating reamer as an extension of the finish reamer rather than make a separate reamer. Some of the older type bullets made it necessary to throat the barrel ahead of the chamber and as some of these bullets are still in use, barrels for these must be so throated. As the chamber must be made at least longer than the cartridge case, to allow for forward
stretch of the case, and as the front end of the lands of the chambering reamer must be sloped forward at an angle of 45 to 60 degrees and these edges given clearance as the lips of a twist drill are in order to enable them to cut, the chambering reamer cuts away the lands of the barrel for some distance ahead of the mouth of a new cartridge case. This fact, taken in relation to our modern shape bullet which starts to taper toward the point from the mouth of the cartridge case, results in bullet jump if the throating of the barrel ahead of the chamber is carried very far. In fact, a barrel for a
Detail of how the teeth of a burnishing reamer are stoned.
cartridge using a modern shape bullet needs only a touch with a throating reamer to give clearance for the bullet and if the chamber is more than longer than the cartridge case, the barrel will usually need no throating at ail.
High-speed steel, hardened and fluted with four flutes, can be purchased from steel companies, one of which is the Central Steel and Wire Co. of 4545 South Western Blvd., Chicago, Illinois. This would require grinding to shape and size for a chambering reamer of the roughing type. This can be done in a lathe with an electric tool post grinder. This four-fluted shape is known as the standard cruciform section and is sup plied in a number of sizes from outer diameter with %2" solid-center section on up to 2outer diameter.
Roughing reamers are usually driven by machine, using a floating drive so that the reamer lines up properly with the bore. A simple type of this drive is a machine attachment shank- for the reamer with a hole drilled in it slightly larger than the reamer shank which slips into it. A pin hole, at right angles to the axis of the reamer, is drilled through the shank of the reamer for a drive pin. This pin hole in the reamer shank is slightly larger than the drive pin which is a tight drive fit in the hole drilled for it through the machine drive shank. This drive shank is sometimes used for a reamer stop on the roughing reamer, in which case the reamer shank is short and the hole in the front end of the drive shank is drilled out, for a short distance, large enough to go over the flutes of the reamer the proper distance to act as a stop against the end of the barrel, the hole in the shank being enough larger than the reamer flutes to allow the reamer to float.
In using this machine drive shank for a reamer stop on a barrel such as the Krag or the '98 model Mauser, which are flat across the breech end, the end of the reamer drive shank is left flat, but in rough reaming barrels such as the Springfield or Enfield which have a tapered lead into the rear end of the chamber the front end of the reamer drive shank is machined with a 45-degree slope forward. This same type of reamer stop may be used on the finish chamber reamer if it is machine driven to within a few thousandths of an inch of the finish size, after which the reamer is removed from the machine and driven by hand for the last few thousandths and a reamer stop slipped over the shank and held on a flat ground on the shank of the reamer, using one or two set-screws in the side of the stop.
Both the roughing and finishing reamers have pilots on the front end which ride upon the tops of the lands in the barrel to keep the chamber in line with the bore. These pilots should be a very close fit in the bore, not more than .001" smaller than the bore diameter and are hardened as the balance of the reamer is and are ground and polished to a very high polish to prevent
Sectional views of rifle chambers showing the metal removed by the various reamers—A, the rough chambering reamer—B, the finishing reamer—and C, the burnishing reamer.
scratching the lands. Half an inch is a sufficient length for these pilots and the front and rear edges of this pilot scction are slightly rounded off to prevent a sharp edge which would scratch the lands of the barrel. These pilots are solid, being part of the reamer itself.
Some gunsmiths prefer a floating pilot, which has an advantage when a number of barrels are to be chambered, as the bore diameter of barrels may vary enough so that a pilot that fits the lands of one may be too tight for another one. By having a few pilots in each size varying slightly in diameter, these varying bores may be fitted. This floating pilot is a sleeve, the outside of which is bore diameter and the inner diameter of which rides on an extension of the chambering reamer slightly longer than the sleeve. This extension on the reamer is drilled and tapped in the front end for a screw with a thin fillister-type head, this head being
Sectional view of barrel at front end of chamber, showing metal removed by throating reamer just ahead of the chamber neck.
just slightly less in diameter than the outer diameter of the sleeve, thus holding the sleeve in place on the reamer extension.
Throating reamers, if used, have the same type of pilots as the roughing and finishing reamers. Burnishing reamers are used either with or without pilots, being a matter of choice of the factory or individual gunsmith, some claiming that a better burnish is obtained if they are used without pilots. If pilots are used they are of the same type as those used on the other chambering reamers.
When reamers are machine-driven a supply of oil
should be pumped into the barrel under pressure to wash out the chips, or the reamers will lodge in the chamber and break or cut an oversize chamber. If reamers are used by hand, the oil may be supplied by hand from a spouted can, then the reamers must often be removed from the chamber and both the reamer and the chamber thoroughly cleaned, after which a patch is pushed through the barrel to clean the lands and grooves. Lard-oil or black sulphur oil compound may be used, but never machine oil.
If the dimensions of the chamber desired are not at hand in making a chambering reamer, twelve or fifteen factory cartridges of various makes should be obtained and carefully measured for size and angle. A clearance, above the maximum cartridge found, of .002" in all dimensions will produce a good chamber. If head-space gauges are not available the largest cartridge you can obtain in that caliber should be used as a head-space gauge and the chamber carefully cut until the breech will just close without any perceptible effort upon this cartridge.
In using chambering reamers the cutting edges of the reamers should be carefully examined and any scratches or small nicks stoned out. Watch particularly for wire edges upon the cutting edge of a new reamer, using a magnifying glass of good power for this examination. The front of the cutting edge should be well stoned to remove all marks left by the milling cutter on this face. If a scratch appears in the chamber that is not later removed by the burnishing reamer its effect may be minimized by buffing the chamber with a crocus buff, of circular form, held on a small mandrel and driven by a high-speed polisher such as these electric hand grinders which reach speeds of about 25,000 R.P.M. This applies only to scratches that are not deep or wide and are not quite removed by the burnishing reamer.
In stoning the cutting edges of the reamers, to remove
Lathe setup for milling the flutes in a chambcring reamer—with the milling attachment driven by flexible shaft and an adjustable tail center to raise tapered reamer to a level. After the reamer blank is turned to shape, an adjustable tail ccntcr thai can he raised or lowered by screw slides is placed in the tailstock and is raised above the live .spindle ccntcr so that the tapered body of the reamer is raised until its top surface is level. The flutes are then milled in the reamer with the milling attachment. The live spindle is locked with the back gear of the lathe while each flute is being milled.
small nicks or scratches, be careful not to flatten the relief at the edge, as this is of eccentric form, not flat, but do not overdo this eccentric form or you may drop the cutting edge of a reamer tooth below the top of the land and the edge will then do no cutting. If the edge appears slightly dull it may be stoned on the front face to sharpen it, as this will not change the form nor will it reduce the diameter much.
In making chambering reamer blanks, cartridges can be measured for angle with a protractor. Take measurements at several different points around the body of several cartridges, as the cartridge case is not a perfect form, due to air or lubricant in the forming dies. Be careful that primers do not protrude on cases that you are measuring or this will throw your measurements off.
Barrel drills are short, about 2" long, and instead of having two cutting edges and two grooves as the ordinary twist drill has, it has a single cutting edge and a single vee-shaped groove running straight back from the point. The included angle of the drill point is the same as of the twist drill, 118 degrees. The vee-groove cut the length of the drill and almost to its center in depth, has an included angle of 90 to 100 degrees. The front end of the drill is ground for relief all around, back of the cutting edge, just as the lips of a twist drill are relieved. A small flat is left on the point of the drill, corresponding in size to the thickness of the web of a twist drill of like diameter. On the opposite side of the drill from the vee-groove a small hole is drilled lengthwise through the body of the drill for the passage of oil under pressure from the oil tube to which the drill is attached. On the rear end the diameter of the drill is reduced for a length of about so that the drill drive tube, which also carries the oil supply, may be brazed onto the drill. The drill itself is of high-speed steel and the drive tube is of high-carbon-steel.
The drive tube has a vee-groove pressed into it, longer than the length of the barrel blank, matching the groove cut in the drill. This groove carries the returning oil and the chips out of the barrel. After the drill is brazed to the tube the joint is ground or filed smooth. The tube should be very slightly less in diameter than the drill, so that it will not lodge in the bore. The drill is ground with a slight taper to the rear from the front, matching the tube for diameter where they meet, and giving a slight body-clearance to the drill.
A split cast-iron block is mounted on the tool rest of the lathe. It is the full width of the top of the compound rest and has a tongue on the bottom that fits
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