A boring machine is a machine tool used to enlarge existing holes with a single point cutting tool. Boring machines are capable of producing very accurate holes with fine finishes. There are several different types of boring machines, each with unique capabilities and applications.
Page Contents
How does a boring machine work?
All boring machines work on the same basic principles. The workpiece is rigidly clamped on the machine’s table or directly to the machine spindle. The boring tool is fed into the existing hole in the workpiece and advanced axially while being rotated. The rotating boring tool cuts away material to enlarge the hole to the desired diameter. The main ways boring machines differ are in how the workpiece is positioned and how the boring tool is fed.
Positioning the workpiece
On vertical boring machines, the workpiece is mounted vertically on the machine’s table or directly to the spindle. The boring tool is advanced horizontally into the workpiece. For large workpieces, the boring tool is moved vertically on a rail and the workpiece remains stationary. On horizontal boring machines, the workpiece is mounted horizontally on the table and the boring tool is advanced vertically into the workpiece from above.
Feeding the boring tool
The boring tool may be automatically or manually fed into the workpiece. On manually operated machines, the operator must carefully control the inward feed of the boring tool. On computer numerical control (CNC) boring machines, the boring tool feed rate is programmed into the machine controller. Power feeds and automatic feeds that hydraulically advance the boring tool are also common.
Major components of boring machines
While boring machine configurations vary, most share some common components:
- Base – Provides support for other components and absorbs cutting forces
- Table – Workpiece is securely mounted on the table
- Column – Supports radial arm that positions boring tool
- Spindle – Rotates the boring tool at high speeds
- Feed mechanism – Advances boring tool into workpiece
- Controls – Manual or CNC controls adjusting boring tool movement
Base
The base is the foundation of the boring machine. It is constructed from cast iron or welded steel and must be very rigid and vibration resistant to provide stable support during boring operations. The mass of the base damps vibrations and absorbs cutting forces.
Table
The table sits atop the base and is used to securely hold the workpiece. Some tables provide manual positioning via hand cranks. Precision boring operations require the table to be aligned perfectly parallel and perpendicular to the boring tool’s feed direction.
Column
The column rises vertically from the base or from the back of the table. It supports the radial arm, allowing it to swing in a horizontal arc. This permits radial adjustment of the boring tool to different positions over the table.
Spindle
The spindle is contained within the radial arm and provides the rotating power for the boring tool. Spindle speeds are variable, with higher speeds used for smaller boring tools. Spindles must run very true and smooth for precision boring work.
Feed mechanism
The feed mechanism controls the inward advance of the boring tool into the workpiece. This may be powered, automatic, or manual. Precise control over the feed rate improves hole size accuracy and finish.
Controls
Boring machines utilize manual hand wheels, hand cranks, power feed controls, or CNC controls. CNC machines allow easy programming of automated boring cycles. Manual machines rely on the skill of the machinist.
Types of boring machines
There are several common types of boring machines designed for different applications:
Vertical boring mills
Vertical boring mills (VBMs) have a vertically oriented spindle that uses a boring head to perform most operations. The workpiece is mounted directly to the massive rotary table, allowing turning functions. VBMs are very rigid and versatile for medium to large workpieces.
Horizontal boring mills
Horizontal boring mills (HBMs) have a horizontally oriented spindle and a vertically adjustable table. The workpiece is mounted on the table. HBMs can handle very large workpieces and provide high accuracy through rigid construction.
Jig borers
Jig borers are designed for precision hole boring. They utilize an inverted vertical spindle and extremely accurate table positioning. Precision ground ways and leadscrews provide positioning accuracy within millionths of an inch for jig boring.
Specialized boring machines
There are also special boring machines for specific applications such as cylinder boring, line boring, and internal carbide boring. Gun barrel boring machines and deep hole boring machines are variants.
Boring tools
Common cutting tools used on boring machines include:
- Single point boring bars – For general internal boring applications
- Boring heads – For larger diameters or simultaneous multiple cutting edges
- Carbide boring bars – For high production CNC boring
- Micro bore tools – For precision holes down to 0.001″ diameter
Single point boring bars
Single point boring bars hold a replaceable insert in the end of the bar. They are capable of boring holes with diameter ranges up to approximately 2 inches.
Boring heads
Boring heads hold multiple boring bars so several cutting edges engage the work simultaneously. This allows larger diameters to be bored as well as reducing cutting time.
Carbide boring bars
Carbide tipped boring bars provide a durable cutting edge capable of high production boring of cast iron, steel alloys and other hard materials. Used primarily on CNC boring mills.
Micro bore tools
Very small diameter boring tools with replaceable solid carbide cutters are available for precision boring operations. Capable of boring holes smaller than 0.001″ diameter.
Boring accessories
Boring operations often require additional accessories such as:
- Steady rests – Support long slender workpieces
- Boring heads – Contain multiple replaceable boring bars
- Boring inserts and bars – Provide the cutting action
- Tool holders – Hold boring bars and prevent slippage
- Digital readouts – Display precise boring tool position
- Coolant systems – Flood work area with cutting fluid
Steady rests
Steady rests support long workpieces close to the cutting area, preventing deflection of the workpiece under cutting forces. This improves accuracy of the bored hole.
Boring heads
Multiple boring bar boring heads allow faster cutting by engaging the workpiece with several cutting edges simultaneously. Various cutter head configurations suit different boring applications.
Boring inserts and bars
Carbide, high speed steel, ceramic, diamond, and cBN boring inserts and bars provide the cutting action for boring tools. Optimal cutting edge technology improves hole size and finish.
Tool holders
Tool holders properly secure boring bars to the spindle of the boring machine. Various tool holder styles such as ISO, CAT, and HSK are available. Collet holders provide maximum rigidity.
Digital readouts
Digital readouts precisely display the boring tool position and feed to facilitate highly accurate boring adjustment. This enhances the operator’s ability to bore holes within tight tolerances.
Coolant systems
Coolant systems flood the cutting area and boring tool with a cutting fluid to cool the cutting action, lubricate, and flush away chips. This improves finish and allows higher cutting speeds and feeds.
Boring machine operations
Typical boring machine operations include:
- Facing – Squaring the workpiece surface
- Spot boring – Accurately locating holes
- Drilling – Producing starter holes for boring
- Counterboring – Squaring and sizing existing holes
- Reaming – Smoothing and finishing hole sizes
- Trepanning – Producing large diameter flat bottom holes
Facing
Facing operations square the workpiece surface prior to boring by bringing the rotating boring tool up to the edge surface and taking a light cut. This ensures the workpiece surface is perpendicular to the bored holes.
Spot boring
Spot boring slightly countersinks starter holes at precise locations. This accurately locates where the full size hole will be bored to ensure position accuracy.
Drilling
Boring machines can be equipped with a drilling spindle to produce starter holes for boring operations. CNC machines allow automatic programmed cycles with spindle changes from drill to bore.
Counterboring
A counterboring cycle enlarges an existing hole and creates a precise 90 degree shoulder surface. This squares and sizes holes to specifications prior to finish reaming.
Reaming
Reaming slightly enlarges hole diameter while significantly improving hole roundness, straightness, and surface finish. Produces precision holes sized within tight tolerances.
Trepanning
Trepanning uses a special boring tool to cut large diameter flat bottom holes. Allows large holes with minimal distortion to the workpiece.
Boring machine accuracy
The three primary factors affecting boring machine accuracy include:
- Machine rigidity – More mass and stiffness improves accuracy
- Precision ways – Minimizes vibration and deflection
- Tolerances – Component manufacturing and assembly tolerances
Machine rigidity
The stiffness of the machine frame, spindle, bearing housings, and slides directly affects boring accuracy. Mass and rigidity allow the machine to absorb cutting forces without distortion of components.
Precision ways
The precision ground rails and leadscrews that control slide motion must be very accurate to avoid introducing vibration. Turcite coated ways also help improve boring precision.
Tolerances
Manufacturing tolerances of each component as well as assembly tolerances also affect the machine’s capability. Tight tolerances result in better accuracy but increase costs.
Boring machine maintenance
To sustain accuracy and boring performance, boring machines require regular maintenance including:
- Way lubrication – Keep precision ways well oiled
- Spindle bearings – Ensure proper spindle bearing lubrication
- Gib adjustment – Tighten gibs to eliminate play without binding
- Scraping – Maintain geometric accuracy by scraping mating surfaces
- Leveling – Use precision levels to align machine perpendicularity
Way lubrication
Frequent lubrication of way surfaces reduces friction and wear to retain accuracy. Oil or grease is manually applied or automatically pumped to ways.
Spindle bearings
Spindle bearings must be periodically inspected and lubricated as needed to prevent wear and ensure proper running tolerances are maintained.
Gib adjustment
Gib clearances on slide ways should be adjusted to remove excess clearances while still allowing full slide travel. This minimizes vibration during boring.
Scraping
Over time mating surfaces may suffer geometric distortion. Precision hand scraping can true and refine the mating surfaces to restore accuracy.
Leveling
Boring machines use precision levels to align the spindle and table perfectly perpendicular and parallel to each other. Periodic realignment improves boring quality.
Advantages of boring machines
Key benefits of boring machines include:
- Extremely accurate hole sizing and location
- Fine surface finishes
- Versatile capabilities beyond just boring
- Rigid construction for chatter-free cutting
- Automation and programming capabilities
Accurate hole sizing and location
Precision boring machines can repeatedly bore holes with dimensional accuracy down to 0.0002″ and location accuracy to 0.001″. This level of hole position precision facilitates precise alignment of components.
Fine surface finishes
Proper feeds, speeds and rigidity allow boring machines to consistently produce hole surface finishes under 10 microinches. Smooth, precise holes improve part performance.
Versatile capabilities
Beyond just boring holes, machines can face, turn, drill and tap holes. Some VBMs allow complete machining of complex parts on one machine.
Rigid construction
Massive cast iron or welded steel construction damps vibration for smooth, chatter-free boring. Holes maintain roundness without distortion.
Automation capabilities
Boring machine automation allows fast setups, loading/unloading and programming of complex boring cycles. Reduces labor while improving productivity.
Boring machine applications
Boring machines are commonly used in applications such as:
- Automotive – Cylinder boring, connecting rods, gears
- Aerospace – Landing gear, wings, hydraulic components
- Medical – Implants, surgical tools
- Moldmaking – Precise alignment of components
- Die/Stamping – Accurate punched holes
- General machining – Hole boring is common
Automotive
Automotive boring applications include cylinder boring, connecting rod alignment boring, camshaft boring, brake rotor resurfacing, and transmission component boring.
Aerospace
Aircraft components such as wings, landing gear, and hydraulic valves often undergo precision boring for weight reduction and performance.
Medical
Boring ensures dimensional integrity and cleanliness of surgical tools and implants. Knee and hip implants often require sub-millimeter accuracy.
Moldmaking
Extremely precise alignment boring of mounting plates and components is critical to injection mold accuracy and performance.
Die/Stamping
Boring is used to produce the female punch/die holes that form holes in stamped parts. Hole location and cylindricity is critical.
General Machining
Almost all machined parts require some bored holes as part of the manufacturing process. Hole size, location, finish must adhere to specifications.
Conclusion
Boring machines utilize single point or multi-edge cutters to accurately enlarge and finish existing holes. Rigid yet dynamic machine construction coupled with precision ground ways provide micron-level boring accuracy and fine surface finishes. Advanced controls and automation facilitate fast setups, changeovers and processing for high productivity. While options vary, common components such as massive bases, adjustable tables, and rotating spindles form the foundation of the machine’s capabilities.
Boring is one of the most commonly used hole machining processes, providing precise alignment and sizing of holes in components across every manufacturing sector. As technology continues advancing, boring machines become ever more capable and automated – expanding the benefits of precision boring to more and more applications.