Hand of Spiral and Hand of Cut
The hand of a reamer cut refers to the direction of rotation (right or left) and may be determined by inspection of the chamfer end of the reamer when mounted so as to make a cut. If the rotary motion of the reamer is counterclockwise, cut is right-hand; if the rotary motion is clockwise, cut is left-hand.
The hand of the spiral or helical reamer may be determined by viewing the reamer from either end. If the flutes twist away from the observer in a clockwise direction, the spiral is right-hand; if the flutes twist away from the observer in a counterclockwise direction, the spiral is left-hand.
Most reamers are right-hand cutting and may have straight flutes, left-hand spiral flutes or right-hand spiral flutes. Straight flutes cost less originally and are easiest to sharpen or recondition. This type of reamer has proved satisfactory for a great many applications. When selecting reamers for machine tools with play in the gears or with spindles not in the best condition, it usually is advisable to choose those with left-hand spiral flutes. This type of reamer
has a negative axial rake and therefore requires no more pressure to feed the tool into the work. The additional pressure and the hand of the spiral opposite to the hand of the cut reduce the tendency for the reamer to jump ahead when easier cutting is encountered because the spindle is under tension and the gears are held in contact. For machine tools in very good condition,
right-hand spiral-fluted reamers are satisfactory. They are inherently free-cutting and require less power; however when used on a worn machine, they tend to dig into the workpiece, cause chatter, and produce a rough hole.