Steady-Rest

Long workpieces cause problems that short ones do not. A 500mm shaft supported at both ends deflects under its own weight by a fraction of a millimeter. A 2000mm shaft deflects by several millimeters. That deflection pulls the hole off-center. Steady rests fix this. But only if they are set up correctly. A misaligned steady rest is worse than no steady rest — it forces the workpiece into a bend that the drill then follows. ...

Thin wall tube collapse during deep hole drilling is a problem I have encountered on hydraulic cylinders, gun barrels, and structural tubing. The cutting force pushes the tube wall inward, the drill binds in the reduced diameter, and both the tube and the tool are damaged. Prevention requires managing the forces on the wall and providing adequate support. Problem Description A thin wall tube collapses when the radial component of the cutting force exceeds the buckling strength of the wall section. The tube wall deflects inward under the drill tip, and the bore diameter effectively shrinks. The drill then jams because the bore is smaller than the drill head. ...

Why Thin Wall Cylinders Vibrate Thin wall cylinders vibrate during deep hole drilling because the wall flexes under cutting forces. The ratio of bore diameter to wall thickness determines how susceptible a cylinder is to vibration. In my experience, cylinders with a diameter-to-wall-thickness ratio above 10:1 will vibrate under normal cutting conditions. When the cylinder wall flexes, the cutting tool encounters an inconsistent depth of cut. The drill digs in deeper when the wall deflects away, then cuts less when the wall springs back. This alternating force creates chatter marks on the bore surface and can chip the cutting edges of the drill in extreme cases. ...

The Geometry and Function of Textile Spindle Shafts Textile spindle shafts are long, thin shafts that rotate at high speeds. Many have a through-hole for lubrication or weight reduction. A typical spindle shaft might be 500-1000mm long with a 10-20mm through-hole. I have worked with shafts up to 1,500mm in length that required an 8mm through-hole. Those are the most difficult jobs because the length-to-diameter ratio exceeds 180 to 1. ...

Workholding is more important in deep hole drilling than in most other machining operations. The cutting forces are high, the cycle times are long, and a part that shifts even 0.1mm during drilling can produce a scrap bore. I’ve used many workholding methods for deep hole drilling. Each has its place depending on the part geometry and production volume. Chucks Chucks are the standard method for holding round parts. A three-jaw or four-jaw chuck grips the OD of the part at the headstock end. The chuck provides the rotational drive if the workpiece rotates. ...