This form of reamer has its cutting edges only on the end, the grooves being cut the entire length of body to reduce the amount of frictional bearing surface and to furnish a channel to conduct the lubricant to the cutting lips. In case there are blowholes or other imperfections in the material being operated on, this reamer will cut a more nearly parallel hole than the fluted chucking reamer.
Fig. 56 shows the ordinary form of rose chucking reamer. The shank is turned to finish size; if it is to fit a holder, it is left slightly larger and turned or ground to size after hardening. The body is turned .015 to .020 inch above finish size and the flutes cut; the size is stamped as shown, and the reamer hardened a little above the body. It is customary, when grinding a rose reamer, to make it a trifle smaller on the end of the body next to the shank - a taper of 1/4000 inch in the length of the cutting part gives good results.
Fig. 56. Rom Chucking Reamer with Straight Shank for Screw or Chucking Machines.
Courtesy of Union Twist Drill Company, Athol, Massachusetts.
Small rose reamers can be made of drill rod, which runs very true to size, if ordered by the decimal equivalent rather than by the drill gage number, or in terms of common fractions. For instance, if drill rod is wanted of a size corresponding to No. 1 Brown and Sharpe drill gage, the size will be much more accurate if ordered as .228 inch diameter, rather than by the gage.
Fig. 57. Small Reamer "Necked Down".
The drill rod may be sawed to length, put in the lathe chuck, and cornered for the cutting lips. When making small reamers that are not to be ground to size after hardening, it is advisable to "neck them down" back of the cutting edge, as shown in Fig. 57. The drill rod often swells or expands at a point where the hardening ends; and by necking down and hardening into the necking, this difficulty is overcome.
Small rose reamers may be given three cutting edges. The flutes may be filed with a three-square or a round-edge file. If a three-square file is used, a groove of the form shown in Fig. 57 may be made. This has a tendency to push the chips ahead when cutting, while a groove filed with a round-edge file, if it is of a spiral form, will draw the chips back into the flute, provided it is a right-hand helix, as shown in Fig. 58.
Fig. 58. Reamer with Right-Hand Helix.
Rose reamers intended for reaming holes of exact size must be ground to correct dimensions after hardening, but small reamers intended for reaming holes where exactness of size is not essential may be made to size before hardening, and the cutting edges backed off with a file for clearance. If reamers are ground on the circumference for size, the lips or cutting edges should be given clearance by grinding. After grinding, the corners of the cutting edges next to the body of the reamer, as shown at the right end of Fig. 56, should be rounded by oil-stoning.