A drilling machine rotates a drill with its spindle and feeds the tool axially with a sliding quill. The work remains fixed on the table. This calculator converts an entered cutting-speed target and drill diameter into spindle RPM, then compares that target with an actual RPM.
Drilling Machine Interactive Calculator
Enter drill diameter, a cutting-speed target and the actual RPM. Move the quill slider to inspect axial feed while the spindle rotates. The work is shown with an existing sectioned bore.
Equation Used
- D in mm, V in m/min, n in rpm.
- Entered target cutting speed is independent of the actual RPM.
- Quill extension positions the tool; no feed-per-revolution input.
- Illustrative 118 degree point and 30 degree helix; over 16 mm tools use a reduced shank in the drawing.
- Stationary sectioned work has a pre-existing bore; no material-removal calculation.
Target speed is supplied by the user. The illustration shows rotation and manual quill positioning; it does not simulate cutting or recommend feeds.
Rotation and feed are separate motions
The motor drives the spindle inside the head. An arbor and chuck connect the spindle to the drill. The quill houses the spindle bearings and slides vertically, carrying the rotating tool toward the work.
The illustration shows a column drill press, its fixed head and table, a vise holding the work, and a three-spoke quill handle. Change the quill extension to move the tool. The handle turns with the axial displacement while the spindle continues to rotate.
The work is shown in section with a pre-existing bore so the tool position is visible. This is a motion illustration rather than a simulation of material removal. The bore remains visible as the quill moves up and down; chip formation is outside the illustration.
Compare a speed setting
Use a cutting-speed target supplied for the actual tool, work material and operation. Enter the drill’s cutting diameter and compare the resulting spindle speed with the machine setting. This calculator does not choose a target from material alone.
The drill press drawing is a general arrangement, not a scale drawing or capacity claim for a named machine. Tools wider than 16 mm are drawn with a reduced shank so the tool remains visibly gripped by the illustrated chuck.
The quill control only positions the tool. It does not specify feed per revolution, thrust, motor power or cutting time.
Drill diameter, cutting speed and RPM
For drill diameter D in millimetres and spindle speed n in revolutions per minute, actual peripheral cutting speed is V=Ï€Dn/1000 in metres per minute. For an entered target Vc, the corresponding spindle speed is ntarget=1000Vc/(Ï€D).
The speed ratio is n/ntarget. The RPM difference is n−ntarget, so a negative result means the selected speed is below the target. These comparisons do not predict tool life or establish a safe operating speed.
The displayed point has an illustrative 118° included angle. Its axial height is D/(2tan 59°). The tool starts 15 mm above the work when quill extension q=0. Its point depth below the work top is max(0,q−15), not the full-diameter bore depth.
The manual feed handle is shown using an illustrative 20 mm pinion radius: its angular change is q/20 radians. The quill-position control is not a timed feed-rate input.
A 12 mm drill and a 22.6 m/min target
For D=12 mm and Vc=22.6 m/min, the target corresponds to approximately 599 rpm. At an actual 1200 rpm, the peripheral speed is 45.24 m/min, about twice the entered target.
Doubling the diameter at the same target halves the calculated target RPM. Doubling actual RPM doubles actual cutting speed. Changing the quill position moves the tool but does not change either speed calculation.
At zero actual RPM, the spindle stops and actual cutting speed is zero. The target RPM remains available, and the quill can still be positioned manually.
What the calculator does not decide
Diameter and RPM determine peripheral speed, but they do not determine a suitable tool, feed, coolant strategy or workholding arrangement. Tool geometry, material, machine limits and the operation still matter.
The illustration uses schematic machine dimensions, a 30° flute helix and a 118° point. It does not reproduce a particular drill-press model or recommend those tool angles for every material.
Rotation is shown at one hundredth of actual speed so the spindle, chuck and flutes can be inspected. The quill follows the position slider directly. No cutting force, runout, hole tolerance, wear life, chip evacuation or cycle-time result is calculated.
Drilling-machine questions
Does the quill rotate?
The sleeve slides axially. The spindle rotates inside it and drives the chuck and tool.
Where does the target cutting speed come from?
It must be selected for the actual tool and operation. The calculator converts that target into RPM; it does not supply a material recommendation.
Why is the animation slower than the stated RPM?
The rotational display is slowed 100 times to make the tool visible. The numerical result still uses actual RPM.
Does the depth readout mean the full-diameter hole is that deep?
No. It is the tool-tip position below the work top. The conical point extends farther than the full-diameter portion of the drill.
Why is there already a bore in the workpiece?
The sectioned bore makes the tool position visible. It remains fixed during quill movement because this illustration shows motion rather than material removal.
References
Grizzly G7947/G7948 drill-press manual, Identification and Controls & Components, describes the general component arrangement. The animation uses schematic machine dimensions.
Sandvik Coromant: drilling formulas and definitions gives the relationship between diameter, cutting speed and spindle speed. The selected cutting-speed input is not a recommendation from that source.
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