Drilling generates a moment (torque) that tries to spin the part around the drill axis. As the drill exits the bottom of the hole, the torque spikes briefly — this is the breakthrough moment when unsecured parts spin suddenly. Unlike milling or turning, where cutting forces are relatively continuous, drilling has this characteristic spike that can overcome friction-based clamping that seemed adequate during the cut.
The other drilling-specific force is thrust — the downward push of the feed. Thrust tends to hold parts against the table rather than lift them, which is why some light work can be hand-held. But thrust on a diagonal or angled hole creates a lateral component that slides the part. And on blind holes, the full thrust load is there for the entire cut.
Workholding for drilling must resist both the rotational moment and the breakthrough spike. Friction alone is rarely sufficient.
A machine vise — a vise designed to bolt to the drill press table — is the correct solution for most drilling work on prismatic parts (blocks, bar stock, plate stock with parallel faces). The vise clamps the part mechanically, eliminating reliance on friction, and the vise itself is bolted to the table so it cannot rotate.
Use a drill press vise that is sized for your parts. A vise that is too small grips the part near its edges with insufficient bearing area. A vise that is too large for small parts may not close far enough to grip properly. Vise jaws should contact the part at a height that puts the clamping force well below the drill entry point.
Align the vise to the table once and leave it. If you have to reposition the vise for each part, you lose the consistency benefit. For production work, mark the vise position with a scriber or use tooling pins in the T-slots to fix the vise position permanently.
For large parts that do not fit in a vise, C-clamps and step clamps secure the work directly to the table. Step clamps (the T-slot clamps with a step block and a hold-down bolt) are better than C-clamps for drill press work because they bolt into the T-slots and cannot slip sideways. C-clamps rely on friction against the table surface and can move under the breakthrough spike.
Clamp near the drill point — the closer the clamp is to the hole location, the more effectively it resists the rotational moment. Clamping at the far end of a long part and drilling near the unclamped end is poor practice; the part acts as a lever with the clamp as the fulcrum and the drill as the force, and the free end can lift or swing.
Use at least two clamp points for any work that is not in a vise. Two points resist rotation that a single clamp point cannot stop. Three clamps on long parts.
Drilling round stock — drilling a transverse hole through a bar or rod — requires a V-block to register the part and prevent it from rolling under the drill. A V-block provides two contact lines along the bottom of the rod, giving stable support and centering. The drill enters on the centerline of the rod without the rod rolling to one side.
Clamp the rod into the V-block with a strap clamp or U-bolt before drilling. Even short rods can roll dramatically at breakthrough. A V-block without a clamp is better than nothing, but it is not secure workholding for production work.
For cross-drilling in multiple positions around a rod (drilling radial holes at different angles), a V-block with an indexing capability or a simple positioner made from angle iron lets you rotate the rod to the next position without losing center registration.
When you run the same part repeatedly, a purpose-built fixture is almost always worth making. A simple drilling fixture: a base plate that references the part in a fixed position, with a bushing plate that guides the drill into the correct location. The part drops in, references against the locating features, and the bushing guides the drill. No layout, no center punch, no measuring per piece — just load, drill, unload.
Drill bushings — hardened steel inserts that fit into the bushing plate — guide the drill tip accurately and prevent the drill from wandering on entry. They also protect the fixture from wear. For high-volume work, replaceable drill bushings are inexpensive and extend fixture life significantly.
Simple fixtures can be made from aluminum or cold-rolled steel. Drill bushings are catalog items available in standard sizes for fractional, letter, and metric drill diameters. A basic fixture for a plate with two holes in specific locations can be built in an afternoon and will pay for itself in the first production run.
Hand-holding a part for drilling — holding it directly by hand without a vise or clamp — is acceptable only for very small holes in thin material where breakthrough torque is negligible. The rule many shops use: 1/4" diameter and under, in material 1/4" thick or less, may be hand-held if the part is large enough to grip safely. Anything larger requires mechanical clamping.
Never hand-hold round stock. Never hand-hold a part that is nearly the same size as the drill diameter (the part will be thrown if the drill catches). If you cannot get a good grip on enough of the part to keep it out of the drill path when it spins, clamp it.
A drilling fixture positions the drill precisely. A dull drill that deflects undoes all that precision. Sharp, geometrically correct cutting edges are what let a bushed fixture produce accurate holes — not just any hole.
Send Your Drills →