A reamer is a tool that makes a smooth, accurate hole. In many cases, however, reamers are used to enlarge cored holes, or holes already drilled, without particular reference to the exact size or condition of the hole. Reamers may be classified according to shape as follows: straight reamers, taper reamers, and formed reamers. Reamers are made solid, adjustable, and with inserted blades. Solid reamers, Fig. 47, are so called because the cutting teeth and head are made from one piece; they have no means of adjustment as to size. The cutting teeth of the inserted-blade reamers are made from separate pieces of steel and inserted in the head, as shown in Fig. 48. The adjustable reamer may be made with inserted teeth, or with cutting teeth solid with the head; but in either case it has some means of adjusting the size.

Fig. 47. Solid Reamer.

Fig. 48. Reamer with Inserted Blades Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.

Straight Reamers

Under this heading the following kinds of reamers are to be found: fluted hand reamers, fluted chucking reamers, rose reamers, single-lip reamers, and three- and four-lipped roughing reamers.

Fluted Hand Reamers

This reamer is made straight on the cutting lips, with the exception of a short distance at the end, A, Fig. 49, which is slightly tapered in order that the reamer may enter the hole. In making such reamers, use steel from 3/32 inch to 1/8 inch above finish size. Turn a chip off the outside surface to a depth of 1/32 inch, and anneal; then turn A and B, to sizes .010 to .015 inch larger than finish size; turn C to finish size; mill the end D square for a wrench. The reamer is now ready to have the flutes cut. Number of Cutting Edges. Fluted reamers designed to remove but a small amount of stock, and intended to cut holes to an accurate size, are rarely given less than six flutes. Below are given the number of cutting edges advisable for solid reamers whose flutes are milled by cutters made to give the proper shape:

Fig. 49. Proper Proportions for Fluted Hand Reamer.

Reamers 1/8" to 7/16' in diameter should have 6 teeth Reamers 1/2' to 11/16' in diameter should have from 6 to 8 teeth Reamers 3/4' to 1' in diameter should have 8 teeth Reamers 1 1/16' to 1 1/2' in diameter should have 10 teeth Reamers 1 9/16' to 2 1/5' in diameter should have 12 teeth Reamers 2 1/4' to 3" in diameter should have 14 teeth.

Formerly it was considered necessary to have an odd number of cutting edges; but an even number, if unevenly spaced, will be as satisfactory. The chief objections to an odd number are the difficulty experienced in calipering, unless a ring gage is used, and the great cost of grinding.

Fig. 50 shows a form of cutter that makes a strong reamer tooth and allows the chips to be removed very readily. These cut the tooth ahead of the center, and should be given a negative rake of about 5 degrees. In general, a reamer will cut more smoothly if the tooth has a slight negative rake, as it then takes a scraping cut.

Fig. 50. Shape of Cutter for Reamer.

Depth Of Cut

With this form of flute, the depth of cut must be so gaged that the land will be about \ the average distance from one cutting edge to the other; if cut deeper, the teeth will be weak and have a tendency to spring; if not so deep, there will not be room for the removal of the chips. Below are tabulated the number of cutters, Fig. 50, for various sizes of reamers.

Spacing Of Teeth

In order that reamers may be calipered readily when grinding, if the teeth have been unevenly spaced, the teeth must be diametrically opposite each other; the unevenness in spacing must be between adjoining teeth. This is done by cutting one tooth, then tinning the spiral head of the milling machine half-way round, by giving the index pin twenty revolutions, and then cutting the opposite tooth. When the flutes are cut in pairs, the number of times the cutter must be set for depth of cut is reduced one-half. Fig. 51 shows an end view of a reamer having the first pair of flutes cut as described. The irregularity of spacing is obtained by moving the index pin a different number of holes for each adjoining pair of flutes. This irregularity need not be great, a variation of 2, 3, or 4 degrees from an angle corresponding to regular spacing, is generally regarded as good practice.

Finishing Processes. Hardening

In order that a reamer may not spring when hardened, great care should be exercised in heating. If a muffle furnace is at hand, a uniform heat can be obtained. If heated in a blacksmith's forge, the reamer should be placed in a tube to prevent the fire from coming in contact with the steel, and should be turned frequently to secure uniform results. In cooling, it should be held in a vertical position to avoid springing, and worked up and down in the bath.

Fig. 51. Reamer with First Pair of Flutes Cut.

If the reamer is one inch in diameter or larger, it should be removed from the hardening bath when it stops, "singing", and plunged into oil, and allowed to remain until cold. The temper may be drawn to a light straw color. If reamers are hardened by the pack-hardening process, the danger of springing is greatly reduced.

Straightening

The straightening should be done before drawing the temper. When drawing the temper, the heat should be applied evenly, or the piece will spring from uneven heating.

If a reamer springs while hardening and tempering, it may be straightened by the following method:

Place the reamer between the centers of the lathe; fasten a tool, or a piece of iron or steel having a square end, in the tool post, Fig.52, placing the square end against the reamer at the point of greatest curvature. The surface of the reamer should be covered with a thin coating of sperm or lard oil. With a spirit lamp, a plumber's hand-torch, or a bunsen burner, heat the reamer evenly until the oil commences to smoke. Pressure may now be applied by means of the cross-feed screw, slowly forcing the reamer over until it is bent a trifle the other way. It should be cooled evenly while in this position, after which the pressure may be relieved and the reamer tested for truth. If it does not run true, the operation should be repeated. This method of straightening is equally effective when applied to other classes of work.

Fig. 52. Diagram Showing Method of Straightening a Bent Reamer.

Grinding

Before grinding a reamer, be sure that the centers of the grinding machine are in good shape; then clean the centers of the reamers. The reamer should first be ground to run true. It may be ground to within .001 or .002 inch of finish size, larger reamers having the larger margin. In backing off a reamer tooth for clearance, use an emery wheel of as large diameter as can be used without striking the cutting edge of the next tooth. The correct clearance is given by a finger which can be adjusted. Fig. 53 shows an end view of a reamer being ground for clearance, together with the finger and the emery wheel. The emery wheel should run in the direction indicated by the arrow, in order that the pressure of the wheel will tend to force the reamer tooth down on the finger B. To give clearance, the finger is adjusted so that the cutting edge is below the line of centers, as shown. The lower the finger, the greater the amount of clearance. Unless a free-cutting wheel, without glaze is used, the temper will be drawn, and the reamer rendered worthless. To avoid softening the teeth, the stock must be removed by a succession of light cuts going entirely around the reamer each time the adjustment is changed.

A reamer will soon lose its size if the clearance is ground to the edge of the teeth; consequently it is best to grind to within from .01 to .015 inch of the edge, according to the size. The reamer is then brought to an edge and to the desired size by oil-stoning. To do satisfactory work, the stone should be free-cutting; a stone of medium grade is best for removing the stock, and a fine stone for finishing the cutting edge. An oil-stone should not be used dry; the face must be kept free from glaze. If there are deep depressions or marks in the stone it should be faced off on a wet grindstone.