How to Read a Drill Press Quill: Depth Stops and Graduations

The quill on a drill press is one of the most useful precision features in the shop, and one of the most ignored. Most operators use it the same way they use a hand drill: lower it until it looks deep enough, then raise it back up. That approach works for one-off holes in wood. It does not work for production machining, where every hole needs to be the same depth, every time, without the operator measuring each one.

Understanding how to actually use the quill — the graduated sleeve, the depth stop nut, the quill lock — turns a drill press from a rough positioning tool into a repeatable production machine. Here is how it works.

What the Quill Is and How It Moves

The quill is the cylindrical sleeve that houses the spindle and moves up and down through the head casting. When you push the feed handles, you are extending the quill downward against a return spring. When you release the handles, the spring returns the quill to its rest position.

The quill has two relevant features for depth control:

• The graduated sleeve (or depth scale): A ruled scale, usually in 0.001" or 1mm increments, marked on the quill body or on a separate scale plate adjacent to the quill. This tells you how far the quill has traveled from its rest position.
• The depth stop assembly: A threaded rod with two lock nuts (sometimes called a stop nut and a jam nut) that limits the maximum downward travel of the quill.

Understanding both, and how they work together, is the foundation of repeatable depth drilling.

Reading the Quill Graduation Scale

With the quill at rest (fully retracted, spring at maximum), the graduation scale reads zero — or its maximum value, depending on how your machine is marked. On most American drill presses, zero is at the top of travel and the numbers increase as the quill extends downward. On some import machines, the scale reads the opposite way.

To read current quill position: note the index line (usually a scribed line on the head casting or a separate pointer) and read the corresponding graduation on the quill. On a press with 0.001" graduations, you can read position to ±0.005" with practice.

The graduation scale is not a substitute for a depth stop. Reading the scale requires keeping your eye on it while feeding, which means your attention is not on the workpiece or the cut. The depth stop is the right tool for controlling maximum depth — the scale is for observing current position and for setting the stop.

Setting the Depth Stop

The depth stop assembly consists of a threaded rod mounted vertically on the drill press head, with a collar or nut that contacts a stop surface as the quill extends. When the stop contacts its surface, the quill cannot travel further.

Setup procedure:

1. Zero the quill. Retract the quill fully to its rest position. This is your reference point.
2. Install your drill and workpiece. Chuck the drill you will use. Clamp the actual workpiece in the vise or fixture.
3. Find the surface contact point. Lower the quill slowly until the drill tip just touches the top surface of the workpiece. Note the graduation reading at this point — call it the surface position.
4. Calculate target depth. Add your required hole depth to the surface position. If the drill tip touched the surface at 0.750" of quill travel and you want 0.500" deep holes, your target stop position is 1.250" of quill travel.
5. Set the stop nut. Adjust the stop nut on the depth stop rod until it will contact its stop surface when the quill reaches your calculated position. Most depth stop assemblies have a scale on the rod itself — set it to the total travel figure you calculated.
6. Lock the jam nut. Thread the jam nut up against the stop nut and tighten them against each other. This prevents the stop nut from vibrating loose during production.
7. Test the stop. Feed the quill down until it hits the stop. Measure the resulting hole depth with a depth micrometer or depth gauge. Adjust and re-test until the depth is on target.

Once set, every subsequent hole drilled to the stop will be the same depth, without measuring, without watching the scale, without any operator judgment during the cut.

The Quill Lock

The quill lock is a separate control — usually a lever or knob on the side of the drill press head — that clamps the quill at whatever position it currently occupies. It serves two distinct purposes that are often confused.

Purpose 1: Holding depth while work is repositioned. If you are drilling a series of holes at the same depth in multiple workpieces, you can drill the first hole to the depth stop, then lock the quill at that position. With the quill locked, you can reposition subsequent workpieces under the locked quill and use the locked spindle height as a reference. This is useful when the quill return spring would otherwise fully retract between holes.

Purpose 2: Rigid spindle for non-drilling operations. When using the drill press for light milling, reaming, or counterboring, locking the quill eliminates quill chatter and provides a more rigid spindle. The drill press is not a milling machine, but for light operations on soft materials, a locked quill significantly improves surface quality.

What the quill lock is not: It is not a substitute for a depth stop. Do not try to use it for depth control by locking it mid-stroke. The lock mechanism is not designed for precise positioning — it clamps wherever the quill happens to be, which varies with operator feel. Always use the depth stop for repeatable depth.

Blind Holes, Through Holes, and the Depth Stop

The setup procedure differs slightly depending on what you are drilling.

Through holes: The quill travel needed exceeds the material thickness, so the depth stop can be set generously — just enough to ensure the drill exits the bottom fully. Many operators disable or fully back out the depth stop for through-hole work and let the drill clear the bottom naturally. If breakthrough must be controlled (to avoid excessive exit burr or to prevent damaging the fixture), set the stop so the drill exits by one drill diameter past the bottom surface.

Blind holes to specific depth: Use the full procedure above. The key measurement error to avoid is not accounting for the drill point geometry. A standard 118° point drill forms a cone at the bottom of any blind hole. If you want 0.750" of full-diameter depth, you need to drill the hole deeper than 0.750" to account for the point cone — add approximately 0.3× the drill diameter as a correction. A 1/2" drill needs roughly 0.150" additional travel to put 0.750" of full-diameter depth in the hole.

Spotfaces and counterbores: When drilling a spotface (a flat-bottom shallow recess), the depth stop is essential. Spotfaces typically need to be cut to a tight depth tolerance — within 0.005–0.010". Set the stop carefully, test on scrap, and lock the jam nut securely.

Why Production Shops Rely on This

In a shop running production work — same part, dozens or hundreds of times — the depth stop does two things that matter economically. First, it removes operator variability from the hole depth dimension. Every operator, on every shift, gets the same result because the machine controls the depth, not judgment. Second, it speeds up the operation. The operator does not need to watch the scale, measure, or pause — they feed to the stop, feel the stop engage, and retract. Cycle time drops.

For shops drilling tapped blind holes, the depth stop is particularly critical. A tap drilled too shallow cannot cut full threads to depth. A tap drilled too deep may break when the tap hits the bottom. Consistent drill depth is the foundation of consistent tap depth.

The quill, depth stop, and quill lock on even a basic drill press give you the tooling to hold ±0.010" depth repeatability across a full production run. Most shops are leaving that capability unused because nobody showed them how to use the stop assembly. Now you know.