Appearance
A rough-sawed bar end walks on entry, breaks tools, and produces scrap. Proper end preparation takes minutes per bar. Skipping it costs broken gun drills and scrapped parts. The preparation step is not optional.
Bar Cutting Methods
| Method | Cut Quality | Typical Cost | Best For |
|---|---|---|---|
| Abrasive cut-off saw | Rough, burrs | Low | Small diameters, quick cuts |
| Band saw | Moderate, minimal burrs | Low–medium | Most production work |
| Cold saw | Clean, square | Medium | High-volume, consistent lengths |
| Lathe cut-off | Excellent, square | Higher (slower) | Critical end prep in one setup |
| Saw + lathe finish | Excellent | Medium | Recommended best practice |
Recommended Practice
For best results, cut bars to length on a band saw or cold saw, leaving 3–5 mm excess for end facing. Then face the end square in a lathe before drilling.
End Preparation Requirements
End Face Requirements
| Requirement | Specification | Why |
|---|---|---|
| Squareness to axis | Within 0.05 mm over bar diameter | Ensures drill enters perpendicular |
| Flatness | No visible wobble when checked against a straightedge | Prevents coolant leakage at bushing |
| Surface finish | Ra 3.2 µm or better | Seal surface for coolant bushing |
| Burrs | None — deburr all edges | Burrs scratch bushing and cause misalignment |
Chamfer Specifications
The entry chamfer guides the drill and protects the bushing:
| Hole Diameter | Chamfer Angle | Chamfer Width |
|---|---|---|
| Under 10 mm | 30° | 1–2 mm |
| 10–25 mm | 30° | 2–3 mm |
| 25–50 mm | 45° | 3–5 mm |
| Over 50 mm | 45° | 5–8 mm |
Tip: Use the same angle on the chamfer as the drill point angle for best centering. A 30° chamfer for a 30° gun drill point centres more accurately than a 45° chamfer.
Centre Drill Mark
A centre drill mark at the hole location is essential for drill entry:
- Use a centre drill that matches or is slightly larger than the drill tip web thickness
- Depth: 1–2 mm minimum, or until the full centre drill diameter engages
- Location: concentric within 0.05 mm of the hole centre
Material Handling for Long Bars
| Bar Length | Handling Method | Recommended Equipment |
|---|---|---|
| Up to 1 m | Manual handling OK | Bar rack, end support |
| 1–3 m | Manual with assistance | Roller stand, bar trolley |
| 3–6 m | Mechanical handling required | Crane + bar sling, motorized roller conveyor |
| 6 m+ | Full mechanical handling | Overhead crane, bar feeder system |
Safety Considerations
Warning: Long bars (3 m+) are heavy and unstable. Always secure bars against rolling. Use bar end protectors to prevent injury from sharp ends. Never handle bars longer than 2 m without mechanical assistance.
Preparation Workflow Integration
Standalone Prep Station
| Equipment | Purpose | Estimated Cost |
|---|---|---|
| Band saw or cold saw | Cut to length | $3,000–15,000 |
| Lathe (manual or CNC) | Face, chamfer, centre drill | $10,000–40,000 |
| Bar rack and storage | Organize raw material | $1,000–5,000 |
| Roller stands or conveyor | Move bars between stations | $2,000–8,000 |
Combined Lathe Prep
For shops with a CNC lathe, combine all preparation steps in one operation:
- Face the end square
- Chamfer the OD
- Spot drill or centre drill the hole location
- (Optional) Start the pilot hole with a short drill
This single-setup approach produces the most accurate end preparation and adds minimal cycle time.
Inspection of Prepared Stock
| Check | Method | Acceptance |
|---|---|---|
| End squareness | Precision square + feeler gauge | < 0.05 mm gap |
| Chamfer dimensions | Chamfer gauge or optical comparator | Within 0.2 mm of spec |
| Centre drill depth | Depth measurement | 1–2 mm full engagement |
| Centre drill concentricity | Dial indicator | Within 0.05 mm of bar OD |
| Bar length | Tape measure or height gauge | Within 0.5 mm of target |
FAQ
Can I drill without end preparation on soft materials?
Not recommended. Even in aluminium, a rough end causes drill skidding on entry, which produces an oversize or misaligned hole start.
How much bar length should I add for end preparation?
Add 3–5 mm to the finished part length for end facing. This allows cleaning up the saw-cut surface while maintaining the final dimension.
Should I centre drill on the bar end or in the existing hole?
Centre drill on the solid bar face at the hole centre location. The centre drill mark guides the gun drill on entry and prevents walking.
Can I use the same preparation for BTA drilling?
BTA drilling typically requires a pilot hole rather than a centre drill mark. The pilot hole is drilled to a depth of 1–2× diameter and must be concentric within 0.02 mm.
What is the most common stock preparation mistake?
Inconsistent chamfer dimensions. Operators who hand-chamfer with a file or deburring tool produce chamfers that vary by 1–2 mm, causing inconsistent drill entry and bushing wear.
Stock preparation requirements vary by hole size, material, and drilling process. Adapt these guidelines to your specific application. This article reflects industry practice as of 2026.