Workholding

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. ...

Workholding is the bottleneck that nobody budgets for. When I walk into a shop that is struggling with deep hole drilling throughput, nine times out of ten the fixturing is the problem, not the machine. Modular fixturing systems have changed how I approach setup planning, and the numbers speak for themselves. The Case for Modular Fixturing Dedicated fixtures for deep hole drilling parts commonly cost $2,000 to $8,000 each and take four to eight weeks to manufacture. For a shop running fifty different part numbers, that investment becomes prohibitive quickly. Modular fixturing, built from standard base plates, locating towers, clamp brackets, and support elements, can cover 80% of those parts with a single system investment of $15,000 to $30,000. ...

Thin wall stainless steel tubing is used in sanitary, pharmaceutical, and food processing applications. The wall thickness is often 2-5mm with a bore diameter of 20-60mm. The challenge is supporting the tube without collapsing it. I have worked with 304L, 316L, and 2205 duplex tubing across wall thicknesses from 1.5mm to 6mm, and the support method changes for each combination of diameter and wall. The cutting forces from gun drilling push the tube wall inward. If the wall is not supported, the tube collapses. Once collapsed, the tube is scrap — there is no recovering a collapsed thin wall tube. The support method must be rigid enough to resist the cutting forces but compliant enough not to mark or distort the tube surface. ...

A fixture is a custom workholding device designed for a specific part. Unlike standard chucks and steady rests, fixtures are built to match the part geometry exactly. A good fixture reduces setup time and improves consistency. I’ve designed and used fixtures for all types of deep hole drilling work. The same principles apply regardless of the part shape. Design Principles Support the part at the bore location. The most important principle. The part should be supported as close as possible to where the drill enters and exits. Unsupported span allows the part to deflect. ...

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. ...