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How to Drill on a Mill
Guide · Updated October 28, 2026
Drilling on a mill gives far better hole position than a drill press because the table moves in measured steps. The process is locate, spot, drill, and sometimes ream or bore to finish.
Check hole position
Check hole spacing with a pin, calipers or height gage verified against gage blocks. Check it with a mic you've verified against gage blocks; the free Gage Block Calculator builds the stack.
Step by step
- Hold the part: Clamp the part in a trued vise on parallels, with room under the hole for the drill to break through.
- Find an edge: Pick up the part edges with an edge finder and zero the DRO or dials.
- Move to position: Move to the hole location, approaching from the same direction to take out backlash, and lock unused axes.
- Spot drill: Spot the hole with a spot or center drill so the drill starts true.
- Pilot if large: Drill a pilot about the size of the next drill web for drills over about 1/2 in.
- Drill: Drill at the right RPM and steady feed, pecking deep holes to clear chips.
- Finish: Ream or bore if the hole needs size or finish, and deburr both sides.
Worked example
1/2 in hole in 1018 steel with an HSS drill at about 80 SFM: RPM = 80 × 3.82 / 0.5 ≈ 610. At 0.005 in per rev, feed ≈ 610 × 0.005 ≈ 3 in/min. Spot with a 90° spot drill, drill a 3/16 in pilot, then the 1/2 in drill, pecking once the depth passes about 3 diameters.
Holes off position
A drill that walks or a hole off location usually means no spot, a dull or unevenly sharpened drill, or backlash in the table. Spot first, use a sharp drill, and approach each hole from the same side.
Drill press vs mill
A mill is more rigid and accurate, but quill feeding is slower. Use a mill for holes that need to be on position; a drill press is fine for clearance holes.
Tips
- Spotting: center and spot drilling.
- Speeds: drilling speeds and feeds.
- Deep holes: peck drilling.
- Locate edges: using a wiggler.
FAQ
What RPM to drill steel on a mill?
About 80 SFM for HSS in mild steel: RPM ≈ 80 × 3.82 ÷ drill diameter.
Do I need to spot drill on a mill?
Yes for accurate holes; it keeps the drill from walking.
Should I drill a pilot hole?
For drills over about 1/2 in, a pilot about the web size makes drilling easier and more accurate.
How do I keep holes on position?
Spot first, approach from the same direction and lock unused axes.
Can a drill make an accurate size hole?
Drills cut slightly oversize; ream or bore for close tolerances.
Related guides and calculators
- How to Center Drill and Spot Drill
- Drilling Speeds and Feeds
- Peck Drilling Basics
- How to Ream a Hole
- How to Bore on a Mill
- How to Use a Wiggler
- Tap Drill Chart Explained
- How to Spotface a Hole
- How to Sharpen a Drill Bit
- How to Counterbore on a Mill
- How to Tap on a Mill
- Leadscrew Backlash Basics
- How to Use a Center Punch and Prick Punch
- How to Use a V-Block for Drilling Round Stock
- All free machinist calculators
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