Bridge Mills

Absolute Machine Tools has been importing, distributing, and servicing CNC bridge mills since its inception in 1988. Our history with these big machines assures our expertise when pairing our customers’ applications with the right machine. Brands such as Johnford and APEC, are the two types of options we offer because they support the entire spectrum of bridge cutting including box ways and geared heads to linear ways and motors.

Johnford Bridge Mills

Johnford bridge mills, or double column machining centers, are built for machining heavyweight workpieces while performing deep-cutting milling, drilling and boring operations:

• Strong box ways support the weight of the table and workpiece, while the double columns provide a stable and rigid framework to support the gantry, spindle and tool head.
• Guideways and ballscrews in the columnsallow for controlled movement of the bridge for positioning the tool head or workpiece during machining operations.
• The columns, box ways, and gantry all work together to distribute loads and forces generated during machining helping to maintain accuracy and reduce vibrations.

Johnford bridge mills are available in a wide variety of configurations and can be custom designed and made to fit specific machining needs.

Spindle Options: A wide range of spindle choices from both 40 and 50 taper to HSK-63A and 100A are available, depending on specific applications.

Configurations: A full range of highly engineered configurations including W axis (cross rail up and down controlled by CNC), full 5-face machining with multiple heads and automatic attachment changer, and full 5-axis articulating heads for simultaneous machining in both high speed and heavy duty versions. This includes:

Starting with our smallest DMC-900 with 36” x 36” x 30” travels to our giant sliding column SDMC-20000 with 720” x 240” x 120” (42” Z + 78” W axis) travels, we can supply virtually any size and any configuration necessary to get the job done right. 

APEC Bridge Mills

APEC’s MT series of 5-axis high-speed double-column machining centers are designed for unparalleled precision and efficiency, especially when machining aluminum alloy structural parts for aerospace and high-precision molds.

• Construction of the Duo Block design for the machine’s framework enhances rigidity and machining stability.
• The machine’s 5-axis capabilities allow for superior accuracy when machining in X, Y, and Z axes while simultaneously rotating A and B axes using direct drive motors for high-end complex parts processing.
• APEC machines are built with linear guideways and linear motors for lightning fast machining, incredibly high tolerances and accuracies, and pristine surface finishes.
• Rapid traverse rate of 1181″/min and high-speed ballscrews for acceleration/deceleration ranges from 16.4 ft./sec2 to 197 ft./sec2 ensure unparalleled time-saving efficiency in every operation.
• Built with AGA or GTW spindles with max speeds of 15,000 and 24,000 RPMs.
• Travels range from 78.74″ to 118.11″ in X, 78.74″ in Y, and 33.46″ in Z.
• High-speed automatic tool changers with HSK63A or HSK100A tool shanks for 32 and 40 tool capacities. Heidenhain TNC640 5-axis CNC control or Heidenhain iTNC530 5-axis CNC control both with HR510 MPG.
• All APEC 5-axis double-column machining centers all include a 2-axis head drive by direct drive motors for superior contour finish and complex curved surface machining capabilities.

As the leading machine tool distributor in North America, Absolute Machine Tools remains committed to providing a comprehensive range of machine tools and equipment from reputed brands to cater to several industries.

What Is a Bridge Mill?

A bridge mill, also known as a double column machining center, is a powerhouse in the world of CNC machining. It excels at handling large and complex workpieces, offering unmatched versatility and precision.

Imagine a robust vertical machining center with a fully supported, extended Y-axis. That’s the essence of a bridge mill. This unique design allows the cutting head to travel across the entire width of the table, providing exceptional machining reach for large parts that wouldn’t fit on a traditional VMC.

Here’s what makes bridge mills stand out:

• Superior Work Envelope: Bridge mills conquer limitations posed by VMC bed sizes. They can handle significantly wider and longer workpieces, expanding your machining capabilities.
• Unparalleled Stability: The bridge structure provides exceptional rigidity, minimizing deflection and vibration during heavy-duty machining. This translates to superior surface finishes and tighter tolerances on your parts.
• Enhanced Accessibility: The open bridge design grants easy access to the worktable from all sides, simplifying part loading/unloading, tool changes, and overall machine operation.

In essence, bridge mills offer a powerful combination of size, strength, and user-friendliness. They are ideal for various applications in industries like:

Ready to unlock the potential of bridge mills for your workshop? Explore our selection of high-performance bridge mills above and contact us today to discuss your specific needs.

Benefits of Choosing a Bridge Mill or Double Column Machining Center

Bridge mills and double column machining centers offer a host of benefits that make them a valuable asset in modern manufacturing environments:

• Enhanced Flexibility and Safety: The design of bridge mills allows for exceptional ergonomics and improved safety. Operators can easily set up multiple workpieces on the large table surface, which provides the versatility needed for various production requirements.
• Increased Machine Rigidity and Precision: The dual-column support for the spindle ensures a stable and vibration-resistant machining process. This rigidity translates to higher precision in cutting, allowing the mills to operate at optimal spindle speeds and maintain tighter tolerances.
• Superior Chip Removal: Bridge mills are designed to facilitate excellent chip removal, ensuring a cleaner workspace with reduced manual cleaning. This feature enhances the efficiency of operations and maintains a cleaner work environment.
• Greater Accuracy: With the cutting forces more stable due to the table’s ability to move between columns, bridge mills are inherently more accurate. This stability is crucial for precision machining and achieving the desired tolerances on finished products.
• Reduced Wear and Tear: Thanks to the reduced vibration from the dual-column design, bridge mills experience less wear on their components. This durability leads to lower maintenance costs and prolongs the lifespan of the machine, ensuring a better return on investment.
• Operational Efficiency: Bridge mills are designed to handle a multitude of part types, which increases operational efficiency. This versatility can lead to higher production rates and, as a result, boost profitability for businesses.
• Space Saving: With a smaller footprint than comparable vertical machining centers, bridge mills help optimize valuable floor space in manufacturing facilities. The reduced space requirement can lead to cost savings in facility management and allow for more efficient layout planning.

In essence, bridge mills represent a sophisticated option for manufacturers looking to enhance production capabilities while ensuring high precision, cost efficiency, and better utilization of workspace.

Applications & Industries that Commonly Use Bridge Mills

Bridge mills transcend limitations, making them a coveted asset for various industries. Their ability to handle large workpieces with exceptional precision unlocks a world of possibilities. Here’s a glimpse into how bridge mills empower different sectors:

Aerospace & Defense:

• Precisely machining large airframe components: Fuselage panels, landing gear parts, and engine housings require tight tolerances and superior strength. Bridge mills deliver the accuracy and rigidity needed for these critical aerospace parts.
• Manufacturing complex wing structures: Bridge mills tackle the intricate geometries of modern wing designs, ensuring smooth airflow and optimal performance.

Automotive:

• Handling large engine blocks and cylinder heads: The robust construction of bridge mills allows them to efficiently machine these massive engine components with the precision needed for high-performance vehicles.
• Creating large molds and dies: Bridge mills are instrumental in automotive production, enabling the creation of large molds and dies for stamping body panels and other vehicle parts.

Die & Mold Making:

• Machining complex mold geometries: Bridge mills conquer the challenges of intricate mold designs, allowing for precise machining of cavities, cores, and other features essential for high-quality parts production.
• Handling large mold bases: The expansive work envelope of bridge mills accommodates oversized mold bases, providing the stability and machining reach needed for large-scale molds.

Energy:

• Machining turbine blades: Bridge mills contribute to reliable energy generation by precisely machining complex turbine blades for power plants.
• Manufacturing large generator components: The ability to handle large workpieces makes bridge mills ideal for machining generator housings, rotors, and other vital components.

Heavy Equipment Manufacturing:

• Efficiently machining large construction equipment parts: Bridge mills tackle the heavy-duty demands of this industry, efficiently machining components like crane booms, excavator arms, and bulldozer blades.
• Manufacturing large parts for mining machinery: Bridge mills contribute to efficient mining operations by precisely machining parts for haul trucks, excavators, and other large mining equipment.

The exceptional capabilities of bridge mills make them a valuable asset for companies seeking to:

• Machine large and complex workpieces with superior precision.
• Increase production efficiency and throughput.
• Achieve tight tolerances and ensure dimensional accuracy.

Bridge Mill vs. Vertical Machining Centers (VMC):

• Work Envelope: Bridge mills excel at handling large workpieces due to full support of the table through the entire X axis travel and  their extended Y-axis travel. VMCs, or C-frames, have a more limited work envelope due to the single column and compound table design with the table not being fully supported (overhang).
• Rigidity: The bridge structure of bridge mills provides exceptional rigidity and accuracy, minimizing deflection during heavy-duty machining. VMCs experience more deflection with larger workpieces and have lower table load capacity.
• Accessibility: The ergonomic design of bridge mills grants easier access to the worktable from all sides, simplifying part loading/unloading and tool changes. VMCs have limitations in accessibility because of the table moving in the Y axis.

Bridge Mill vs. Double Column Machining Center (DMC):

The term “double column” is synonymous with “bridge mill.” Both offer the benefits of a large work envelope, high rigidity, and improved accessibility. It’s important to note that the bridge structure itself can vary depending on the size and capacity of the machine. For example, Johnford DMC series mostly features models with one-piece column and bridge castings.

Bridge Mill vs. Vertical Turning Machine (VTL):

These machines serve different purposes:

• Bridge Mills: Ideal for milling complex 3D geometries on workpieces of various shapes and sizes.
• VTLs: Primarily used for turning large cylindrical workpieces. They rotate the workpiece on a horizontal axis while the cutting tool moves along various programmed paths.

Bridge Mill vs. Gantry Mill:

Bridge mills or double column machining centers are often used interchangeably with gantry mills.  Both refer to CNC machines with lengthy tables and a bridge-like structure, also called a gantry, that supports the spindle assembly, enabling machining across a wide work envelope.  However, they differ in movement. Bridge mill tables move back and forth under the fixed gantry (or bridge), while gantry mills allow the gantry (bridge) and columns to move over and across the top of the fixed table.  Gantry mills are also known as sliding double column machining centers because the gantry slides on either box ways or linear rails over the top of the fixed table. (This is instead of the two paragraphs below.

While both bridge and gantry mills are used to machine parts in similar industries, the differences lay in the construction of the machines.  Bridge mill construction typically uses box ways and geared heads and are best used for industrial manufacturing requiring heavy part machining in industries such as automotive, energy, construction, industrial, shipbuilding, military and defense, railway and transportation, and tool and die making.  Gantry mill construction typically employs linear ways and motors and are best used in industries such as aerospace, automotive and mold design where super fine finishes are required.   Both types of machines can cut virtually any type of metal, so it depends upon the design, specifications, and application of the project at hand to determine which machine would be the best choice.

Maintenance and Support for CNC Bridge Mills

Just like a car, a bridge mill is a substantial investment, so practicing preventive and routine maintenance are essential for optimal performance and longevity. It’s important to not only check fluids but also consumable items that wear out through normal use of operation. Both Johnford and APEC supply documentation for routine maintenance with every machine. Below are suggestions from both OEMs on routine preventive maintenance items for CNC bridge mills.

Daily Maintenance

• Check oil levels in every lubrication tank and system throughout the machine and fill the reservoirs back up to the appropriate levels.
• Check all lubricated parts to ensure they are receiving lubrication.
• Check pneumatic gauges to ensure they are reading correctly and maintaining the manufacturers required pressure.
• Look for leaks where air pressure is critical.
• Remove any water that could contaminate critical oils.

Before the machine is put into commission, check the work envelope to ensure all possible obstructions have been removed to avoid damage to the machine, spindle, part(s), or operator.

When the machine is first in process, check to ensure that the coolant levels are sufficient and cooling mechanisms are working properly.

The spindle taper must be kept tidy at all times.  Make sure to clean the taper with the proper cleaning solution and reapply taper lubrication.

If the cycle time is long, remember to keep checking on the machine to ensure everything is running the way it was intended too. If there’s an issue then take immediate measures to cycle stop the machine at the proper time to avoid damage to the machine and injury to the operator or maintenance personnel.

Weekly Maintenance

• Wipe reflectors or sensors of reading devices with clean absorbent cotton or soft gauze to keep it clean and receive exact readings.
• Remove air filters and rinse with a detergent and water to ensure proper air flow and reduce contamination.
• Check the spindle tool clamping and unclamping movement to ensure smooth motion and proper operation.
• Check pumps throughout the machine to verify fluids are circulating properly.
• Watch that the automatic tool changing action is operating properly and precisely as expected.

Six Months Maintenance

• Check spindle preload to ensure accuracy while cutting and spindle longevity.
• Check the gap on the taper gib on every rail to ensure it is not growing.
• Check all wire connecting points, adapters, sockets, and switches that they are functioning normally and free of dust and other contaminants.
• Verify alignment of bridge mill components, including the spindle, table, and tooling to ensure the highest level of precision machining.
• Verify that all installed software is up-to-date to benefit from the latest features and/or fixes.

Annual Maintenance

• Clean relay connections in the electrical cabinet.  After, make certain they are properly connected.  
• Check that the counter weight chain(s) are in normal condition to avoid injury to the operator and the bridge mill.
• Wash coolant tank(s), removing all tramp coolant, and replace with new coolant.  Wear gloves while washing.
• Wash centralized lubricating oil tank(s) and replace with new oils.  Wear gloves while washing.
• Wash forced lubricating oil tank(s) and replace with new oil.  Again, wear gloves while washing.
• Check all points to ensure the bridge mill is properly levelled which will result in proper operation and superior accuracy.
• Analyze and monitor any vibrations to detect imbalances, misalignments or bearing issues or failures.
• Always check all grease and lubrication for metal particles or other contaminants that could result in improper component wear.

Maintenance Notes

• While maintaining, adjusting or repairing, always double check that all power to the machine has been turned off and proper safety procedures are being implemented.
• Power down the bridge mill’s CNC control when replacing or repairing the circuit board so machine does not begin to arbitrarily run or power does not cause additional harm to the board and machine.
• Check that bolts, screws, and other fasteners are secure and in place.  If missing, replace immediately.
• Consider using thermal imaging to identify overheating of components or potential electrical issues.  It’s better to practice this now rather than repairing it later.
• Consider the use of implementing sensors or investing in a monitoring system to track conditions of critical components and cutting in real-time.
• If air, oil and coolant filters do not come clean after washing, replace them with new ones.

If the in-house maintenance team feels that the maintenance or repair is outside their expertise, then contact the manufacturer or distributor that initially sold the equipment. If the bridge mill or any other CNC was purchased through Absolute Machine Tools, we have not only the training and expertise to troubleshoot and repair, but also the proper equipment to ensure success.

Following preventive and routine maintenance schedules are paramount to a bridge mills longevity.  Absolute Machine Tools provides both maintenance and repair services, and offers 3 levels of maintenance packages to fit every manufacturer’s budget.

Lubrication of Machine and Components

Everyone knows that machines are mechanical, and in order to ensure proper operation, they need lubricated during and outside scheduled maintenance times.  

Lubrication of Spindle Bearings

Nearly all spindle bearings on large CNC machine tools, such as bridge mills, use grease for lubrication.  Using grease ensures that the areas most affected by friction are properly lubricated for long periods of time.  If something other than grease were to be used, then operators or maintenance personnel would have to constantly check to ensure proper lubrication of the spindle bearing, which is not feasible for any shop.  High quality grease, as recommended by the manufacturer, should contain good adhesion, water resistance, sealing, and protection against contamination of the spindle bearings to guarantee that the machine’s spindle operates properly and achieves longevity.

Lubrication of Gears

Gears in the gearbox of every machine tool are lubricated by a built-in pump reducing friction and dissipation of heat within.  Always use recommended gear lubrication that meets the demands of high-speed heavy torque operations.

Lubrication of Slide Surfaces

All machines containing slide surfaces, such as box ways, linear rails, table, saddle, spindle housing, and X-Y-Z axis ballscrews, have built-in centralized lubrication systems to continually lubricate those surfaces that are constantly experiencing motion.  The lubrication used for these components must feature wear resistance, pressure resistance, and good adhesive properties to continually guard against wear and vibration.

Manual Lubrication

Not every component on a CNC bridge mill can be maintained on a schedule or by an automatic lubrication system.  Manual lubrication is for those parts or components that either aren’t easily accessed or don’t need to be serviced as often as those listed above.  Parts such as counterweight block chains, sprocket wheels, sliding or movable doors and their rollers, and linear motor roller bearings still need to be checked and occasionally lubed for proper performance and wear and tear.  

Frequently Asked Questions About Bridge Mills