Direct Engagement
The short, sturdy body allows the tool to engage the material directly without wandering.
Drills / Stub-length drills
Screw Machine Length Drill Bits
What Are Screw Machine Length Drill Bits and How Do They Work?
Screw machine length drill bits, often referred to as "stub drills," are specialized cutting tools engineered for maximum rigidity. Originally designed for automated screw machines, their short flute and overall length reduce the leverage forces that cause standard drills to bend or snap during heavy feeds.
Self-Centering
A typical 135-degree split point bites into the metal immediately, eliminating the need for a center punch or spotting drill.
Chatter-Free Cutting
The reduced flute length provides core strength that limits vibration during the cut.
Tight Tolerances
Reduced deflection helps the drill produce round, accurate holes.
Key Features and Benefits of Screw Machine Length Drill Bits
Maximum Rigidity
The short profile resists breakage under normal straight-line drilling forces.
No Spotting Required
The rigid body and split-point geometry can eliminate a separate center-drilling operation.
High Feed Rates
Thick web construction supports faster feeds than standard-length bits.
Tight Space Access
The short profile suits right-angle drills and confined mechanical bays.
Organized Solutions
A complete screw machine drill bit set provides fractional or metric sizes for immediate tool changes.
Screw Machine Length Drill Bits Specifications
| Specification | Range / Details |
|---|---|
| Diameter Range | 1/64" to 1" (Standard, Metric, Wire, and Letter sizes) |
| Flute Length | Significantly shorter than Jobber length (approx. 4x to 5x diameter) |
| Point Angle | Typically 135° Split Point for self-centering |
| Shank Type | Straight Cylindrical |
| Tolerance | Precision ground for high-speed CNC applications |
| Format | Individual bits or a complete screw machine drill bit set |
Materials and Coatings Available for Screw Machine Drill Bits
| Material / Coating | Best For | Key Advantage |
|---|---|---|
| HSS (High-Speed Steel) | Mild steel, aluminum, and general machining. | Economical and resistant to impact and shock loads. |
| Cobalt (HSS-Co) | Hardened steel, stainless steel, and titanium. | Heat resistance supports aggressive feed rates in tough alloys. |
| TiN / TiAlN Coating | Continuous CNC production environments. | Reduces friction and wear to retain the cutting edge over repeated cycles. |
HSS provides impact resistance and economy for general machining, cobalt adds heat resistance in hard alloys, and TiN or TiAlN coatings reduce friction and wear in repeated CNC cycles.
Which Machines Use Screw Machine Length Drill Bits?
Automatic Screw Machines
The original intended machine, used for high-volume automated part turning and hole boring.
CNC Lathes
Mount the bits in turrets to drill into the center of rotating workpieces with minimal deflection.
Handheld Power Drills
Give mechanics and sheet metal workers a short, rigid bit for confined spaces.
Applications and Industries for Screw Machine Drill Bits
Automated Turning
Used in CNC lathes and automatic screw machines to drill holes rapidly in continuous production cycles.
Confined Spaces
Bores clearance and tapped holes where standard jobber drills are too long to fit.
Hard Metal Machining
Cuts stainless steel and titanium where tool rigidity is critical to prevent snapping.
Sheet Metal Fabrication
Drills round holes in thin metals without catching or distorting the material.
Frequently Asked Questions About Screw Machine Length Drill Bits
What is the main difference between jobber length and screw machine length drill bits?
Jobber length bits are longer, all-purpose drills. Screw machine length drill bits are much shorter, which makes them more rigid and limits bending, vibration, and breakage in hard materials.
Do I need a center drill when using screw machine drill bits?
Typically no. Their rigid bodies and common 135-degree split points resist walking, allowing them to drill directly into the workpiece without a pilot or center hole.
Why should I buy a screw machine drill bit set instead of individual sizes?
A set provides an organized index of fractional, wire, letter, or metric sizes. It reduces downtime by keeping a rigid bit available for a range of hole dimensions.
Can I use these bits in a regular hand drill?
Yes. Their short length is useful in tight engine bays and makes them harder to snap accidentally than standard jobber drills.
Are cobalt screw machine bits better than HSS?
Cobalt is better suited to stainless steel, cast iron, titanium, and other hard materials because it retains its edge under high heat. Standard HSS is more economical for softer materials such as aluminum or wood.
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