Hand of Spiral and Hand of Cut Reamers
Hand Spiral and Hand Cut
The left or right hand of a reamer cut refers to the direction of rotation (left or right) 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, the cut is right-hand; if the rotary motion is clockwise, the 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 and are the easiest to sharpen or recondition. This type of reamer has proved satisfactory for 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 less pressure to feed the tool into the work. The additional pressure and the hand of the spiral opposite to the hand of the cut reduces the tendency for the reamer to jump ahead with easier cutting since the spindle is under tension and the gears are held in contact.
For machine tools in excellent 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.