Use of Reamers

It is difficult, if not quite impossible, to drill a hole to an exact standard diameter. For much work, a variation of a few thousandths of an inch from the nominal diameter is of no account. Where greater accuracy than this is required, the holes are reamed, that is, the hole is first drilled somewhat smaller than it is desired and is then reamed out to the proper size with a reamer.

Holes drilled with common chucking drills are usually 1/16 inch under the finish size. A chucking reamer, Fig. 72, is used to enlarge the hole to within about .005 inch of the true size. This reamer is centered on both ends and turned to size. The entering end, which does the cutting, is given a short, sharp taper, while the straight portion serves as a guide to keep the tool in position. By this means, the drilled hole is straightened and brought close to size.

Fig. 72. Flat Chucking Reamer

Fig. 72. Flat Chucking Reamer.

Hand Reaming

To give the hole a smooth surface and a correct diameter, a fluted hand reamer, of which there are various forms, is used. This tool is not intended to remove large amounts of metal, but serves only to increase the size of a hole by a small fraction of an inch up to the diameter required. The hole should not be more than 0.007 inch smaller than the hand reamer. It is evident that if the reamer were to be made of the same diameter throughout its whole length, it would be very difficult to make it enter the hole. In order to facilitate this, it is usually made slightly tapering for a distance from the entering end equal to about one diameter.

One form of reamer has a shallow screw thread cut at the entering end. This thread takes hold of the metal and draws down into the work. When using a reamer, it is always well to pass the entire tool through the hole. The leading end is subjected to the greatest amount of wear because it does the greatest amount of work. If, therefore, only the leading end is put through, the hole will not be of a uniform diameter throughout. Oil should always be used on reamers when they are working in wrought iron or steel.

Fig. 73. Solid Hand Reamer

Fig. 73. Solid Hand Reamer.

The hand reamer, Fig. 73, is the typical form, and one which can be used in many cases in place of special forms. Fig. 74 is better adapted for use in the lathe than the hand reamer. This may follow the chucking reamer to finally finish a hole.

In reaming cored holes, the cylindrical chucking reamer, sometimes called a roughing reamer, is often used. It is made either

Fig. 74. Plain Shell Reamer

Fig. 74. Plain Shell Reamer.

Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.

Fig. 75. Rose Shell Reamer

Fig. 75. Rose Shell Reamer.

Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island rose, Fig. 75, fluted, or with three spiral flutes, Fig. 76, and generally has solid shanks. The last-named style will finish very smooth and close to size when started true by preliminary boring.

Fig. 76. Spiral Chucking Reamer Drill

Fig. 76. Spiral Chucking Reamer Drill.

A solid reamer cannot be sharpened without reducing its diameter; therefore, it must be used carefully in order to prolong its life.

Reamers with adjustable blades meet this objection, but cost much more than the solid form. An expanding reamer, Fig. 77, can be slightly enlarged to compensate for grinding and is then used as a solid reamer. Fig. 78 shows an adjustable reamer with inserted blades.

Hand Reaming 94Fig. 77. Expanding Reamer and Arbor

Fig. 77. Expanding Reamer and Arbor.