Slide 002: Drilling, Boring, and Taper Turning¶
Slide Visual¶
Slide Overview¶
This slide covers secondary lathe operations—center drilling, through-drilling, boring to precision diameters, and methods for cutting tapers on the metal lathe.
Instruction Notes¶
Center Drilling and Drilling¶
Center Drilling: Before drilling or using a tailstock center, create a center drill hole. A combined drill and countersink (center drill, #2 or #3 size) creates a conical guide that prevents the twist drill from walking.
Through-Drilling on the Lathe: 1. Face the workpiece end flat. 2. Start a center drill hole (drill to the full countersink diameter). 3. Replace the center drill with the desired twist drill in a drill chuck (Jacobs chuck in the tailstock). 4. Set RPM for the drill diameter (not the workpiece diameter): RPM = (SFM × 3.82) / Drill Diameter. 5. Peck drill: advance 1-2 drill diameters, retract fully to clear chips, re-advance. Use cutting fluid. 6. Continue until the desired depth is reached.
Key rule: The drill is stationary; the workpiece rotates. This is opposite from a drill press and produces better hole concentricity with the workpiece axis.
Boring¶
Boring enlarges and trues an existing hole to a precise diameter.
When to bore instead of drill: - When the required hole size does not match a standard drill size - When higher accuracy is needed than drilling can provide (drilling: ±0.005"; boring: ±0.0005") - When the hole must be concentric with the workpiece OD - When superior surface finish is required
Boring bar setup: - Select a boring bar diameter that is 60-70% of the hole diameter (maximize rigidity) - Set the boring bar on center height - Minimize overhang—extend the bar only as far as needed to reach the full depth - Set DOC to 0.010-0.030" for roughing, 0.003-0.010" for finishing - Feed at 0.002-0.005 IPR for steel
Taper Turning Methods¶
A taper is a uniformly changing diameter along the workpiece length. Tapers are specified by taper per foot (TPF), angle, or as a ratio.
Method 1: Compound Rest - Set the compound rest to half the included taper angle - Feed manually using the compound handwheel - Best for: short tapers, chamfers - Limitation: manual feed only, limited length
Method 2: Tailstock Offset - Offset the tailstock laterally by a calculated amount - The workpiece (between centers) rotates at an angle to the carriage travel - Offset = (TPF × Workpiece Length) / 24 - Best for: long, shallow tapers (Morse tapers, etc.) - Limitation: only works between centers, distorts center holes
Method 3: Taper Attachment - A taper attachment (if equipped) guides the cross slide at a preset angle while the carriage feeds normally - Best for: production work, repeatable tapers - Advantage: power feed available, no center distortion
| Method | Taper Length | Feed | Precision | Setup Time |
|---|---|---|---|---|
| Compound rest | Short (<3") | Manual | Good | Fast |
| Tailstock offset | Long | Power feed | Moderate | Medium |
| Taper attachment | Any | Power feed | Excellent | Medium |
Key Talking Points¶
- Center drill before every drilling operation—a walking drill is dangerous and inaccurate
- Boring is the most accurate way to produce an internal diameter on the lathe
- Boring bar rigidity is critical—always use the largest bar that fits and minimize overhang
- Each taper method has a best-use case—learn to select appropriately
Learning Objectives (Concept Check)¶
- Can students describe the peck drilling procedure?
- Can students explain when boring is preferred over drilling?
- Can students select the appropriate taper turning method for a given scenario?
Last Updated: 2026-03-19