Drill Runout: How to Measure It and What to Do About It

Runout kills drill bits. It oversizes holes, chews up workpiece material, and puts lateral stress on the cutting edges that no bit geometry can handle for long. Most shops ignore it until something breaks. That's backwards. Measuring runout takes three minutes and a dial indicator. Fixing it usually costs nothing.

Here's the full picture on drill press runout — what it is, where it comes from, how to measure it, and what you can actually do about it.

What Runout Is

Runout is any deviation of the drill's centerline from the true axis of spindle rotation. When a bit is spinning perfectly true, every point on its cutting edge traces an identical circular path. When runout exists, the bit wobbles — one lip cuts deeper than the other, the hole drifts oversize, and the bit experiences bending forces on every revolution.

There are two types. Radial runout (TIR — total indicator reading) is the side-to-side wobble you'd measure at the OD of the shank. Axial runout is front-to-back wobble at the tip. Both matter, but radial runout at the shank is the number most shops track.

Acceptable runout varies by application. General shop work can usually tolerate 0.003"–0.005" TIR. Precision work — reaming setups, multi-step hole operations, anything with a positional tolerance — wants to be under 0.001". Production drilling that's running large volumes of HSS bits should stay under 0.002" to avoid premature edge failure.

How to Measure It

You need a dial indicator, a magnetic base, and a known-good test bar or a straight drill shank. Don't measure on a bit you're suspicious of — measure on a ground test bar first to isolate whether the problem is in the spindle or in the toolholder.

1. Install the test bar or a clean, straight shank in the chuck or collet.
2. Mount the dial indicator on the drill press table with the magnetic base. Position the contact point against the shank about 0.5" below the chuck jaws.
3. Slowly rotate the spindle by hand (power off). Watch the indicator needle travel.
4. Record total indicator reading (TIR) — the difference between the highest and lowest readings through one full revolution.
5. Move the indicator down toward the tip and measure again. Growing runout as you move away from the chuck indicates tool holder or arbor issues. Consistent runout throughout suggests a spindle problem.

Write the number down. If you've never measured this before, don't be surprised if it's worse than expected.

The Five Sources of Runout

1. A Worn or Damaged Chuck

Keyed Jacobs-type chucks wear over years of use. The jaws stop closing concentrically. This is the most common source of runout on older drill presses. Test by measuring TIR at different clock positions — rotate the shank 120° and measure again. If the number changes significantly based on shank orientation but stays the same with a different chuck, the chuck is the culprit.

2. A Dirty or Damaged Taper

Drill press spindles use Morse taper arbors. Any nick, burr, or chip sitting in that taper will throw the chuck off-center. Clean both the spindle taper and the chuck arbor with a clean rag before every serious setup. A single chip the size of a fingernail clipping can add 0.005" of runout.

3. A Bent Drill Shank

Cheap bits and bits that have been dropped have bent shanks. Measure the shank, not the flutes. If the shank runs true and the flutes don't, you have a bent bit — not a machine problem.

4. Off-Center Chuck Jaws

Even on a good chuck, worn jaw serrations can cause one jaw to grip inconsistently. Try tightening the chuck from a different key position. Some chucks have a preferred position where jaw engagement is most concentric.

5. Spindle Bearing Wear

If runout is consistent regardless of chuck orientation or tooling, the spindle bearings are suspect. This is a machine repair job. On a floor drill press, replacement bearings are cheap — usually under $40. On a bench-top unit, sometimes a new press is the better call.

Fixing It

Work from outside in. Start with the cheapest, easiest fixes before touching anything mechanical.

Clean the taper first. Pull the chuck, wipe down both mating surfaces, reinstall firmly. Re-measure. You'll be surprised how often this alone cuts runout in half.

Try a different chuck orientation. Mark the chuck and arbor so you can return to the best position. Rotate 60° increments and measure at each position. On chucks with minor jaw inconsistency, there's often a "best" position with 30–50% less runout than the worst position.

Replace the chuck. A quality Jacobs or Albrecht keyless chuck runs $60–$150. If your current chuck is more than 10 years old and you've never replaced it, a new chuck is the highest-ROI upgrade you can make to drill press accuracy.

Switch to collet holders. ER collet chucks hold much more concentrically than keyed chucks — typically 0.0005"–0.001" TIR on quality units. If you're doing precision work, a drill press collet adapter is worth every dollar.

Replace spindle bearings. If all else fails and runout persists with known-good tooling and a clean taper, it's bearings. Most drill press spindles use two standard deep-groove ball bearings. Look up the part numbers, order from a bearing supply house, and press in replacements.

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Runout is a measurable problem with measurable fixes. Most shops walk past it every day and pay for it in dull bits and oversized holes. Spend the three minutes to check it — you'll either confirm your machine is in good shape or find out why your tooling is dying faster than it should.